Battery monitoring module and power supply system

Abstract

This battery monitoring module comprises: a protection circuit that detects overcharge or overdischarge of a secondary battery; a monitoring circuit that monitors a current flowing in the secondary battery and transmits information indicating that the current is flowing; and a transistor that is turned on or off by the protection circuit and controls the current. The protection circuit turns on the transistor upon receiving the information when the transistor is in an off state.

Description

Battery monitoring module and power supply system

[0001] The present disclosure relates to a battery monitoring module and a power supply system.

[0002] Conventionally, a protection and monitoring circuit has been known that includes a protection circuit that detects at least one of overcharging, over-discharging, and overcurrent of a secondary battery and controls charging and discharging of the secondary battery, and a secondary battery monitoring circuit that calculates the remaining battery capacity of the secondary battery (see, for example, Patent Document 1).

[0003] Patent No. 5564955

[0004] When a protection circuit for a secondary battery detects overcharging or overdischarging of the secondary battery, it transitions to a protection state, turning off a transistor that controls the current flowing to the secondary battery. However, when the protection circuit returns from the protection state, current flows through the parasitic diode of the transistor, which can cause the transistor to heat up.

[0005] The present disclosure provides a secondary battery monitoring module and a power supply system that can suppress heat generation in a transistor when a protection circuit returns from a protection state.

[0006] A first aspect of the battery monitoring module comprises: a protection circuit that detects overcharging or over-discharging of a secondary battery; a monitoring circuit that monitors the current flowing in the secondary battery and transmits information about the current flow; and a transistor that is turned on or off by the protection circuit and controls the current, and when the protection circuit receives the information while the transistor is off, it turns on the transistor.

[0007] A second aspect of the power supply system comprises: a secondary battery; a protection circuit that detects overcharging or over-discharging of the secondary battery; a monitoring circuit that monitors the current flowing in the secondary battery and transmits information about the current flow; and a transistor that is turned on or off by the protection circuit and controls the current, and when the protection circuit receives the information while the transistor is in an off state, it turns on the transistor.

[0008] According to the present disclosure, it is possible to suppress heat generation in a transistor when a protection circuit returns from a protection state.

[0009] FIG. 1 is a circuit block diagram showing an example of a system including a protection circuit according to a first embodiment. FIG. 1 is a diagram for explaining an example of a heat generation phenomenon of a transistor when the protection circuit recovers from an overcharge protection state. FIG. 2 is a diagram for explaining an example of an operation when the protection circuit according to the first embodiment recovers from an overcharge protection state. FIG. 3 is a diagram for explaining an example of an operation when the protection circuit according to the first embodiment recovers from an overdischarge protection state. FIG. 4 is a diagram for explaining an example of an operation when the protection circuit according to the first embodiment recovers from an overdischarge protection state. FIG. 5 is a diagram showing an example of a configuration of a protection circuit according to the first embodiment. FIG. 6 is a timing chart showing an example of an operation when the protection circuit according to the first embodiment recovers from an overcharge protection state. FIG. 7 is a timing chart showing an example of an operation when the protection circuit according to the first embodiment recovers from an overdischarge protection state. FIG. 8 is a circuit block diagram showing an example of a system including a protection circuit according to a second embodiment. FIG. 9 is a diagram showing an example of an operation when the protection circuit according to the second embodiment recovers from an overcharge protection state. FIG. 10 is a diagram showing an example of an operation when the protection circuit according to the second embodiment recovers from an overdischarge protection state. FIG. 11 is a diagram showing an example of a configuration of a protection circuit according to the second embodiment. FIG. 12 is a circuit block diagram showing a modified example of a system including the protection circuit according to the first embodiment.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0011] Fig. 1 is a circuit block diagram showing an example of a system including a protection circuit according to a first embodiment. The system 501 shown in Fig. 1 includes a battery device 401 and an electronic device 300. The system 501 may also include a charger 302 that charges the battery device 401.

[0012] The electronic device 300 is an example of a load that consumes power supplied from the battery device 401. Specific examples of the load include a mobile phone, a smartphone, a tablet device, and earphones. However, the electronic device 300 is not limited to these devices.

[0013] When connected to the battery device 401, the electronic device 300 operates on power supplied from the battery device 401. A charger 302 that charges the battery device 401 is connected to the electronic device 300. Note that the electronic device 300 itself may be a charger that charges the battery device 401.

[0014] The electronic device 300 has a connector 305, a PMIC (Power Management Integrated Circuit) 303, and an internal circuit 304. The connector 305 is a component for electrically connecting the electronic device 300 and the charger 302. The PMIC 303 is a circuit that controls charging of the secondary battery 210 in the battery device 401. The PMIC 303 controls the charging current supplied from the charger 302 to the secondary battery 210 in the battery device 401. The internal circuit 304 is a circuit within the electronic device 300. Examples of the internal circuit 304 include a processor such as a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an interface circuit.

[0015] The PMIC 303 or the internal circuit 304 receives battery information (e.g., information about the remaining capacity of the secondary battery 210) supplied from the terminal I / F of the battery device 401. The PMIC 303 or the internal circuit 304 performs predetermined processing based on the received battery information. For example, the internal circuit 304 performs processing to display the remaining capacity of the secondary battery 210 on a display provided in the electronic device 300.

[0016] The battery device 401 is an example of a power supply system that supplies power to the electronic device 300. The battery device 401 may be external to the electronic device 300 or may be built into the electronic device 300. The battery device 401 is, for example, a battery pack that is detachably attached to the electronic device 300. The battery device 401 may be in a form other than a battery pack.

[0017] The battery device 401 and the electronic device 300 are connected to each other via a plurality of terminals (in this example, an interface terminal (terminal I / F), a positive power supply terminal (terminal P+), and a negative power supply terminal (terminal P-)). For example, the terminals P+ and P- are electrically connected to the charger 302 when charging the secondary battery 210.

[0018] The battery device 401 includes a secondary battery 210 and a battery monitoring device 601 .

[0019] The secondary battery 210 is an example of a chargeable and dischargeable battery. The secondary battery 210 supplies power to the electronic device 300 connected to the terminals P+ and P-. The secondary battery 210 can be charged by a charger 302 electrically connected to the terminals P+ and P-. Specific examples of the secondary battery 210 include a lithium ion battery and a lithium polymer battery. The secondary battery 210 has a positive electrode 211 and a negative electrode 212.

[0020] The battery monitoring device 601 is an example of a battery monitoring module that monitors the secondary battery 210, and transmits battery information including the results of monitoring the secondary battery 210 to the electronic device 300 via the terminal I / F. The battery monitoring device 601 operates using the secondary battery 210 as a power source.

[0021] The battery monitoring device 601 includes, for example, a terminal P+, a terminal P-, a terminal I / F, a terminal B+, a terminal B-, resistive elements R21, R23, and Rsns, a capacitor C21, a power supply line 201, a ground line 202, a switch circuit 203, a protection IC 101, and a fuel gauge IC 701. IC is an abbreviation for Integrated Circuit.

[0022] The battery monitoring device 601 is a component that includes a board on which at least the protection IC 101 or the fuel gauge IC 701 is mounted, for example.

[0023] Terminal P+ is an example of a first positive terminal for connecting a load, and is connected to the power supply line of the electronic device 300. Terminal P- is an example of a first negative terminal for connecting a load, and is connected to the ground line of the electronic device 300. Terminal B+ is an example of a second positive terminal for connecting a secondary battery, and is connected to the positive electrode 211 of the secondary battery 210. Terminal B- is an example of a second negative terminal for connecting a secondary battery, and is connected to the negative electrode 212 of the secondary battery 210.

[0024] Terminal B+ and terminal P+ are connected by a power line 201, which is a positive power path. The power line 201 is an example of a first current path connecting terminal B+ and terminal P+. The power line 201 functions as a charging path through which a charging current of the secondary battery 210 flows and a discharging path through which a discharging current of the secondary battery 210 flows.

[0025] Terminal B- and terminal P- are connected by a ground line 202, which is a negative power supply path. The ground line 202 is an example of a second current path that connects terminal B- and terminal P-. The ground line 202 functions as a charge path through which a charging current of the secondary battery 210 flows and a discharge path through which a discharging current of the secondary battery 210 flows.

[0026] The switch circuit 203 is provided on the power supply line 201 between the terminal B+ and the terminal P+. The switch circuit 203 is, for example, a series circuit including a charge control transistor TR1 and a discharge control transistor TR2 connected in series. The charge control transistor TR1 is a semiconductor switching element that cuts off the charge path of the secondary battery 210. The discharge control transistor TR2 is a semiconductor switching element that cuts off the discharge path of the secondary battery 210.

[0027] 1 , the charge control transistor TR1 cuts off the power supply line 201 through which the charging current of the secondary battery 210 flows, and the discharge control transistor TR2 cuts off the power supply line 201 through which the discharging current of the secondary battery 210 flows. The charge control transistor TR1 and the discharge control transistor TR2 are switching elements that switch the power supply line 201 between conducting and cutting off, and are inserted in series in the power supply line 201. The charge control transistor TR1 and the discharge control transistor TR2 are, for example, N-channel MOSFETs (Metal Oxide Semiconductor Field Effect Transistors).

[0028] The charge control transistor TR1 has a parasitic diode D1 between its drain and source, whose forward direction is opposite to the direction of the charging current of the secondary battery 210. The charge control transistor TR1 is a switching element inserted in series with the power supply line 201 so that the forward direction of the parasitic diode D1 coincides with the direction of the discharging current of the secondary battery 210.

[0029] The discharge control transistor TR2 has a parasitic diode D2 between its drain and source, whose forward direction is opposite to the direction of the discharge current of the secondary battery 210. The discharge control transistor TR2 is a switching element inserted in series with the power supply line 201 so that the forward direction of the parasitic diode D2 coincides with the direction of the charge current of the secondary battery 210.

[0030] The protection IC 101 is an example of a protection circuit used to protect a secondary battery. The protection IC 101 operates using the secondary battery 210 as a power source. The protection IC 101 is a secondary battery protection integrated circuit that includes, for example, a circuit that protects the secondary battery 210 from overcharging and the like by controlling the charging of the secondary battery 210, and a circuit that protects the secondary battery 210 from overdischarging and the like by controlling the discharging of the secondary battery 210.

[0031] The protection IC 101 has a function of protecting the secondary battery 210 from over-discharge and the like by controlling the switch circuit 203. For example, when the detection circuit 222 detects abnormal charging (e.g., overcharging, excessive current in the charging direction (charging overcurrent)), the protection IC 101 protects the secondary battery 210 from abnormal charging by turning off the charge control transistor TR1. On the other hand, when the detection circuit 222 detects abnormal discharging (e.g., over-discharging, excessive current in the discharging direction (discharging overcurrent)), the protection IC 101 protects the secondary battery 210 from abnormal discharging by turning off the discharge control transistor TR2.

[0032] The protection IC 101 includes, for example, a charge control terminal (terminal COUT), a discharge control terminal (terminal DOUT), a power supply terminal (terminal VDD), a ground terminal (terminal VSS), a current detection terminal (terminal CS), a monitoring terminal (terminal VP), and a receiving terminal (terminal RX). These terminals are, for example, external connection terminals for connecting the internal circuit of the protection IC 101 to the outside of the protection IC 101.

[0033] The terminal COUT is connected to the gate (control electrode) of the charge control transistor TR1 and outputs a signal to turn the charge control transistor TR1 on or off. The terminal DOUT is connected to the gate (control electrode) of the discharge control transistor TR2 and outputs a signal to turn the discharge control transistor TR2 on or off.

[0034] The terminal VDD is a power supply terminal of the protection IC 101 and is connected to the positive electrode 211 of the secondary battery 210 and the power supply line 201. The terminal VSS is a ground terminal of the protection IC 101 and is connected to the negative electrode 212 of the secondary battery 210 and the ground line 202 via a resistor element R21. A capacitor C21 is connected between the terminal VDD and the terminal VSS. The terminal VDD is connected to the power supply line 201 between the switch circuit 203 and the positive electrode 211. In this example, the terminal VDD is connected to the power supply line 201 between the charge control transistor TR1 and the positive electrode 211. The protection IC 101 operates with a power supply voltage Vdd applied between the terminals VDD and VSS.

[0035] Terminal CS is a current detection terminal used to detect the charging current or discharging current flowing through the secondary battery 210. Terminal CS is connected to the power supply line 201 between terminal P+ and switch circuit 203 (the source of the discharge control transistor TR2). Resistance element Rsns, which is inserted in series with the power supply line 201, has one end connected to terminal CS and the other end connected to terminal P+ and to terminal VP via resistance element R23. Detection circuit 222 in the protection IC 101 detects the potential difference between terminal CS and terminal VP to detect the charging overcurrent or discharging overcurrent flowing through the secondary battery 210. Resistance element Rsns functions as a sense resistor that detects the current I (charging current or discharging current) flowing through the secondary battery 210.

[0036] The terminal VP is an example of a monitoring terminal used to monitor the potential of the terminal P+. The terminal VP is used, for example, by the control circuit 221 in the protection IC 101 to monitor whether the electronic device 300 or the charger 302 is connected. The terminal VP is connected to the power supply line 201 between the switch circuit 203 and the terminal P+ via a resistor element R23. The terminal VP is electrically connected to the power supply line 201 on the opposite side of the switch circuit 203 from the secondary battery 210.

[0037] Terminal RX is a receiving terminal used to receive information S transmitted from terminal TX of fuel gauge IC 701, and is electrically connected to terminal TX of fuel gauge IC 701. Note that terminal RX is not limited to being a receive-only terminal, and may be a terminal for both transmission and reception. For example, terminal RX may be a general-purpose input / output (GPIO) port.

[0038] The protection IC 101 includes a detection circuit 222 and a control circuit 221 .

[0039] The detection circuit 222 monitors the power supply voltage Vdd between the terminals VDD and VSS to detect overcharge of the secondary battery 210. The detection circuit 222 compares the power supply voltage Vdd with a predetermined overcharge detection voltage Vdet1, and when the power supply voltage Vdd is higher than the overcharge detection voltage Vdet1, generates an overcharge detection signal indicating that overcharge of the secondary battery 210 has been detected.

[0040] The detection circuit 222 detects a charging overcurrent of the secondary battery 210 by monitoring the potential difference ΔV1 between the terminals CS and VP. The detection circuit 222 compares the potential difference ΔV1 with a predetermined charging overcurrent detection voltage Vdet4, and when the potential difference ΔV1 is higher than the charging overcurrent detection voltage Vdet4 with respect to the terminal CS, the detection circuit 222 generates a charging overcurrent detection signal indicating that a charging overcurrent of the secondary battery 210 has been detected. In other words, the detection circuit 222 generates the charging overcurrent detection signal when the voltage of the terminal VP is higher than the charging overcurrent detection voltage Vdet4 with respect to the terminal CS.

[0041] The control circuit 221 controls the charging of the secondary battery 210. When the detection circuit 222 detects overcharging of the secondary battery 210 for a predetermined detection delay time tVdet1, the control circuit 221 outputs a signal (e.g., a low-level gate control signal) that switches the charge control transistor TR1 from on to off from the terminal COUT. When the detection circuit 222 detects a charging overcurrent of the secondary battery 210 for a predetermined detection delay time tVdet4, the control circuit 221 outputs a signal (e.g., a low-level gate control signal) that switches the charge control transistor TR1 from on to off from the terminal COUT.

[0042] By turning off the charge control transistor TR1, the control circuit 221 prohibits current flowing in the direction of charging the secondary battery 210 from flowing through the power line 201. This stops charging of the secondary battery 210, allowing the protection IC 101 to protect the secondary battery 210 from overcharging or charging overcurrent.

[0043] The detection circuit 222 detects recovery from overcharge of the secondary battery 210 by monitoring the power supply voltage Vdd between terminals VDD and VSS. The detection circuit 222 compares the power supply voltage Vdd with a predetermined overcharge recovery voltage Vrel1, and when the power supply voltage Vdd is lower than the overcharge recovery voltage Vrel1, generates an overcharge recovery signal indicating that recovery from overcharge of the secondary battery 210 has been detected. The overcharge recovery voltage Vrel1 is lower than the overcharge detection voltage Vdet1.

[0044] The detection circuit 222 compares the potential of the terminal VP with a state detection threshold that is lower than the potential of the terminal VDD, and when the potential of the terminal VP is lower than the state detection threshold, generates a load connection signal that indicates a state in which a load such as the electronic device 300 is connected to the terminal P+. This is because when a load such as the electronic device 300 is connected to the terminal P+ and the terminal P-, the potential of the terminal VP drops, causing the potential difference between the terminal VDD and the terminal VP to increase.

[0045] When the charge control transistor TR1 is turned off due to the detection of overcharge, the protection IC 101 transitions to a state (overcharge protection state) in which the secondary battery 210 is protected from overcharge by turning off the charge control transistor TR1. In the overcharge protection state, if the control circuit 221 detects that the secondary battery 210 has recovered from overcharge continuously for a predetermined recovery delay time tVrel1 and detects an electrical connection with a load between the terminal P+ and the terminal P-, the control circuit 221 outputs a signal (e.g., a high-level gate control signal) from the terminal COUT that switches the charge control transistor TR1 from off to on. This cancels the overcharge protection operation by the protection IC 101, and the protection IC 101 recovers from the overcharge protection state.

[0046] The detection circuit 222 monitors the power supply voltage Vdd between the terminals VDD and VSS to detect over-discharge of the secondary battery 210. The detection circuit 222 compares the power supply voltage Vdd with a predetermined over-discharge detection voltage Vdet2, and when the power supply voltage Vdd is lower than the over-discharge detection voltage Vdet2, generates an over-discharge detection signal indicating that over-discharge of the secondary battery 210 has been detected.

[0047] The detection circuit 222 detects a discharge overcurrent of the secondary battery 210 by monitoring the potential difference ΔV1 between terminals CS and VP. The detection circuit 222 compares the potential difference ΔV1 with a predetermined discharge overcurrent detection voltage Vdet3, and when the potential difference ΔV1 is lower than the discharge overcurrent detection voltage Vdet3 with respect to terminal CS, the detection circuit 222 generates a discharge overcurrent detection signal indicating that a discharge overcurrent of the secondary battery 210 has been detected. In other words, the detection circuit 222 generates a discharge overcurrent detection signal when the voltage of terminal VP is lower than the discharge overcurrent detection voltage Vdet3 with respect to terminal CS.

[0048] The control circuit 221 controls the discharge of the secondary battery 210. When the detection circuit 222 detects over-discharge of the secondary battery 210 for a predetermined detection delay time tVdet2, the control circuit 221 outputs a signal (e.g., a low-level gate control signal) that switches the discharge control transistor TR2 from on to off from the terminal DOUT. When the detection circuit 222 detects a discharge overcurrent of the secondary battery 210 for a predetermined detection delay time tVdet3, the control circuit 221 outputs a signal (e.g., a low-level gate control signal) that switches the discharge control transistor TR2 from on to off from the terminal DOUT.

[0049] By turning off the discharge control transistor TR2, the control circuit 221 prohibits current flowing in a direction that discharges the secondary battery 210 from flowing through the power line 201. This stops the discharge of the secondary battery 210, allowing the protection IC 101 to protect the secondary battery 210 from over-discharge or discharge overcurrent.

[0050] The detection circuit 222 detects recovery from over-discharge of the secondary battery 210 by monitoring the power supply voltage Vdd between terminals VDD and VSS. The detection circuit 222 compares the power supply voltage Vdd with a predetermined over-discharge recovery voltage Vrel2, and when the power supply voltage Vdd is higher than the over-discharge recovery voltage Vrel2, generates an over-discharge recovery signal indicating that recovery from over-discharge of the secondary battery 210 has been detected. The over-discharge recovery voltage Vrel2 is higher than the over-discharge detection voltage Vdet2.

[0051] The detection circuit 222 compares the potential of the terminal VP with a state detection threshold that is lower than the potential of the terminal VDD, and when the potential of the terminal VP is higher than the state detection threshold, generates a charger connection signal that indicates a state in which the charger 302 is electrically connected to the terminal P+. This is because when the charger 302 is electrically connected to the terminals P+ and P-, the potential difference between the terminals VDD and VP becomes smaller due to the increase in the potential of the terminal VP.

[0052] When the discharge control transistor TR2 is turned off due to the detection of overdischarge, the protection IC 101 transitions to a state (overdischarge protection state) in which the secondary battery 210 is protected from overdischarge by turning off the discharge control transistor TR2. In the overdischarge protection state, if the overdischarge recovery of the secondary battery 210 is continuously detected for a predetermined recovery delay time tVrel2 and an electrical connection with the charger 302 is detected between the terminal P+ and the terminal P-, the control circuit 221 outputs a signal (e.g., a high-level gate control signal) from the terminal DOUT that switches the discharge control transistor TR2 from off to on. This cancels the overdischarge protection operation by the protection IC 101, and the protection IC 101 returns from the overdischarge protection state.

[0053] The fuel gauge IC 701 is an example of a monitoring circuit that monitors the current I flowing through the secondary battery 210 and transmits information about the flow of the current I. The fuel gauge IC 701 detects the current I flowing through the secondary battery 210 and measures the remaining amount (remaining capacity) of the secondary battery 210 using the result of integrating the current value of the detected current I.

[0054] The fuel gauge IC 701 includes, for example, a power supply terminal (terminal BAT), a ground terminal (terminal GND), a current detection terminal (terminal IN1), a current detection terminal (terminal IN2), an interface terminal (terminal A), and a transmission terminal (terminal TX). These terminals are, for example, external connection terminals for connecting the internal circuit of the fuel gauge IC 701 to the outside of the fuel gauge IC 701.

[0055] The terminal BAT is a power supply terminal of the monitoring IC 701, and is connected to the power supply line 201 between the resistive element Rsns and the terminal P+. The terminal GND is a ground terminal of the monitoring IC 701, and is connected to the negative electrode 212 of the secondary battery 210 and the ground line 202. The fuel gauge IC 701 operates on the power supply voltage applied between the terminal BAT and the terminal GND.

[0056] Terminal IN1 is connected to one end of resistor Rsns. Terminal IN2 is connected to the other end of resistor Rsns. Resistor Rsns is an example of a resistor used for current detection in a monitoring circuit. The fuel gauge IC 701 detects the current I flowing through the secondary battery 210 by monitoring the potential difference ΔIN (the voltage generated across resistor Rsns) between terminals IN1 and IN2. The larger the potential difference ΔIN, the larger the value of current I. The fuel gauge IC 701 detects the value of current I corresponding to the magnitude of the potential difference ΔIN.

[0057] When the potential of terminal IN2 is higher than the potential of terminal IN1, the fuel gauge IC 701 determines that the current I is a charging current of the secondary battery 210, and when the potential of terminal IN2 is lower than the potential of terminal IN1, the fuel gauge IC 701 determines that the current I is a discharging current of the secondary battery 210.

[0058] The resistive element Rsns is provided on the power supply line 201 between the transistors TR1, TR2 and the terminal P+. As a result, even if an abnormal current path occurs between the terminal IN1 and the terminal A or the like due to a malfunction of the fuel gauge IC 701 and an overcurrent flows, the overcurrent protection by the protection IC 101 works, improving the reliability of the battery monitoring device 601.

[0059] The fuel gauge IC 701 measures the remaining capacity of the secondary battery 210 using the detected value of the current I, and outputs information including the measurement value as battery information from terminal A. The battery information including the measurement value of the remaining capacity is transmitted to the electronic device 300 via terminal A and terminal I / F.

[0060] The fuel gauge IC 701 transmits information S indicating that a current I is flowing from a terminal TX. The information S is input to a terminal RX of the protection IC 101. Note that the terminal TX is not limited to being a transmission-only terminal, and may be a terminal for both transmission and reception. For example, the terminal TX may be a GPIO port.

[0061] The fuel gauge IC 701 transmits information S indicating whether a charging current or a discharging current is flowing through the secondary battery 210 from the terminal TX to the protection IC 101. This allows the protection IC 101 to acquire information S indicating whether a charging current or a discharging current is flowing through the secondary battery 210.

[0062] Next, an example of the operation when the protection circuit recovers from the overcharge protection state will be described.

[0063] 2 is a diagram illustrating an example of the heat generation phenomenon of a transistor when the protection circuit recovers from the overcharge protection state. The vertical axis of FIG. 2 represents voltage, and the horizontal axis represents time. The solid line represents the voltage at terminal P+, and the dotted line represents the voltage at terminal B+.

[0064] The protection IC 101 detects overcharging of the secondary battery 210 when the power supply voltage Vdd is higher than the overcharge detection voltage Vdet1. When the protection IC 101 detects overcharging of the secondary battery 210, it protects the secondary battery 210 from overcharging by turning off the charge control transistor TR1 so as to cut off the flow of charging current to the secondary battery 210 (overcharge protection state). To return the protection IC 101 from the overcharge protection state, a load such as the electronic device 300 is connected to the terminals P+ and P-.

[0065] However, when a load is connected to the terminals P+ and P- while the charge control transistor TR1 is in the off state, the current (discharge current Idis) that discharges the secondary battery 210 flows via the parasitic diode D1 of the charge control transistor TR1. Therefore, the charge control transistor TR1 may generate heat due to a conduction loss P (=Idis × VF) caused by a forward voltage drop VF of the parasitic diode D1.

[0066] For example, if the charge control transistor TR1 remains off until the power supply voltage Vdd drops below the overcharge recovery voltage Vrel1, the discharge current Idis from the secondary battery 210 to the load continues to flow through the parasitic diode D1, increasing the amount of heat generated by the charge control transistor TR1.

[0067] FIG. 3 is a diagram showing an example of the operation of the protection circuit according to the first embodiment when it recovers from an overcharge protection state. The vertical axis of FIG. 3 represents voltage, and the horizontal axis represents time. The solid line represents the voltage at terminal P+, and the dotted line represents the voltage at terminal B+. When the charge control transistor TR1 is turned off due to overcharge detection (overcharge protection state), and a load is connected to terminals P+ and P-, the discharge current Idis is detected by the fuel gauge IC 701. The occurrence of the discharge current Idis is detected, for example, when the voltage at terminal IN2 becomes lower than the voltage at terminal IN1. In the overcharge protection state, the protection IC 101 continues to turn off the charge control transistor TR1 until it receives information S indicating that the discharge current Idis is flowing from the fuel gauge IC 701. Here, the discharge current Idis is detected earlier than the timing at which the power supply voltage Vdd drops below the overcharge recovery voltage Vrel1. This is because the discharge current Idis flows through the parasitic diode D1 for a certain period of time, causing the power supply voltage Vdd to drop below the overcharge recovery voltage Vrel1.

[0068] When the protection IC 101 receives information S from the fuel gauge IC 701 indicating that a discharge current Idis is flowing in the overcharge protection state, it switches the charge control transistor TR1 from off to on, even if the power supply voltage Vdd has not dropped below the overcharge recovery voltage Vrel1. Note that there may be a predetermined delay due to the circuit operation of the protection IC 101 between receiving the information S and turning on the charge control transistor TR1. However, even including this delay, the timing at which the charge control transistor TR1 turns on upon detection of the discharge current Idis is earlier than the timing at which the charge control transistor TR1 turns on upon detection of the power supply voltage Vdd below the overcharge recovery voltage Vrel1. Therefore, when the protection IC 101 recovers from the overcharge protection state, the time during which the discharge current Idis flows through the parasitic diode D1 of the charge control transistor TR1 is shortened, thereby suppressing heat generation in the charge control transistor TR1. Suppressing heat generation in the charge control transistor TR1 improves the reliability of the charge control transistor TR1.

[0069] When the charge control transistor TR1 is turned on, the conduction loss P of the charge control transistor TR1 is reduced from P1 (=Idis×VF) to P2 (=(Idis)２ × Ron). Ron is the resistance value of the charge control transistor TR1 in the on state, and is smaller than the resistance value when a forward current flows through the parasitic diode D1. For example, from typical values, let the discharge current Idis be 1 ampere, the forward voltage drop Vf of the parasitic diode D1 be 0.6 volts, and the on resistance Ron of the charge control transistor TR1 be 5 milliohms. In this case, P1 = Idis × VF = 600 mW, and P2 = (Idis) ２ ×Ron=5mW, which is a significant reduction.

[0070] When the charge control transistor TR1 is in the off state, the state in which the discharge current Idis flows through the parasitic diode D1 of the charge control transistor TR1 is referred to as a diode conduction state. The potential difference between the terminals P+ and B+ is larger when the parasitic diode D1 is in the diode conduction state than when the charge control transistor TR1 is in the on state. Therefore, the fuel gauge IC 701 may, for example, measure the potential difference between the terminals P+ and B+, and when the measured value is higher than when the charge control transistor TR1 is in the on state, determine that the discharge current Idis is flowing through the parasitic diode D1 of the charge control transistor TR1. When the fuel gauge IC 701 detects that the discharge current Idis is flowing through the parasitic diode D1 of the charge control transistor TR1, it may transmit information S indicating that the discharge current Idis is flowing.

[0071] Next, an example of the operation when the protection circuit recovers from the over-discharge protection state will be described.

[0072] 4 is a diagram illustrating an example of the heat generation phenomenon of a transistor when the protection circuit recovers from the over-discharge protection state. The vertical axis of FIG. 4 represents voltage, and the horizontal axis represents time. The solid line represents the voltage at terminal P+, and the dotted line represents the voltage at terminal B+.

[0073] The protection IC 101 detects over-discharge of the secondary battery 210 when the power supply voltage Vdd is lower than the over-discharge detection voltage Vdet2. When the protection IC 101 detects over-discharge of the secondary battery 210, it turns off the discharge control transistor TR2 to block the flow of discharge current of the secondary battery 210, thereby protecting the secondary battery 210 from over-discharge (over-discharge protection state). To return the protection IC 101 from the over-discharge protection state, the charger 302 is connected to the terminals P+ and P-.

[0074] However, when the charger 302 is connected to the terminals P+ and P- while the discharge control transistor TR2 is in the off state, the current (charging current Ichg) that charges the secondary battery 210 flows via the parasitic diode D2 of the discharge control transistor TR2. Therefore, the discharge control transistor TR2 may generate heat due to a conduction loss P (=Ichg×VF) caused by a forward voltage drop VF of the parasitic diode D2.

[0075] For example, if the discharge control transistor TR2 remains off until the power supply voltage Vdd rises above the over-discharge recovery voltage Vrel2, the charging current Ichg from the charger 302 to the secondary battery 210 continues to flow through the parasitic diode D2, increasing the amount of heat generated by the discharge control transistor TR2.

[0076] FIG. 5 is a diagram illustrating an example of the operation of the protection circuit according to the first embodiment when it recovers from an overdischarge protection state. The vertical axis of FIG. 5 represents voltage, and the horizontal axis represents time. The solid line represents the voltage at terminal P+, and the dotted line represents the voltage at terminal B+. When the discharge control transistor TR2 is turned off due to overdischarge detection (overdischarge protection state), and the charger 302 is connected to terminals P+ and P-, the charging current Ichg is detected by the fuel gauge IC 701. The occurrence of the charging current Ichg is detected, for example, when the voltage at terminal IN2 becomes higher than the voltage at terminal IN1. In the overdischarge protection state, the protection IC 101 continues to turn off the discharge control transistor TR2 until it receives information S indicating that the charging current Ichg is flowing from the fuel gauge IC 701. Here, the charging current Ichg is detected earlier than the timing at which the power supply voltage Vdd rises above the overdischarge recovery voltage Vrel2. This is because the charging current Ichg flows through the parasitic diode D2 for a certain period of time, causing the power supply voltage Vdd to rise above the over-discharge recovery voltage Vrel2.

[0077] When the protection IC 101 receives information S from the fuel gauge IC 701 indicating that the charging current Ichg is flowing in the over-discharge protection state, it switches the discharge control transistor TR2 from off to on, even if the power supply voltage Vdd has not yet risen above the over-discharge recovery voltage Vrel2. Note that there may be a predetermined delay due to the circuit operation of the protection IC 101 between receiving the information S and turning on the discharge control transistor TR2. However, even including this delay, the timing at which the discharge control transistor TR2 turns on upon detection of the charging current Ichg is earlier than the timing at which the discharge control transistor TR2 turns on upon detection of the power supply voltage Vdd being equal to or greater than the over-discharge recovery voltage Vrel2. Therefore, when the protection IC 101 recovers from the over-discharge protection state, the time during which the charging current Ichg flows through the parasitic diode D2 of the discharge control transistor TR2 is shortened, thereby suppressing heat generation in the discharge control transistor TR2. Suppressing heat generation in the discharge control transistor TR2 improves the reliability of the discharge control transistor TR2.

[0078] When the discharge control transistor TR2 is turned on, the conduction loss P of the discharge control transistor TR2 is reduced from P3 (=Ichg×VF) to P4 (=(Ichg)２ × Ron). Ron is the resistance value of the discharge control transistor TR2 in the on state, and is smaller than the resistance value when a forward current flows through the parasitic diode D2. For example, from typical values, let the charging current Ichg be 1 ampere, the forward voltage drop Vf of the parasitic diode D2 be 0.6 volts, and the on resistance Ron of the discharge control transistor TR2 be 5 milliohms. In this case, P3 = Ichg × VF = 600 mW, and P4 = (Ichg). ２ ×Ron=5mW, which is a significant reduction.

[0079] When the discharge control transistor TR2 is in the off state, a state in which the charging current Ichg flows through the parasitic diode D2 of the discharge control transistor TR2 is referred to as a diode conduction state. The potential difference between terminals P+ and B+ is larger when the parasitic diode D2 is in the diode conduction state than when the discharge control transistor TR2 is in the on state. Therefore, the fuel gauge IC 701 may, for example, measure the potential difference between terminals P+ and B+, and when the measured value is higher than when the discharge control transistor TR2 is in the on state, determine that the charging current Ichg is flowing through the parasitic diode D2 of the discharge control transistor TR2. When the fuel gauge IC 701 detects that the charging current Ichg is flowing through the parasitic diode D2 of the discharge control transistor TR2, it may transmit information S indicating that the charging current Ichg is flowing.

[0080] In this way, in the first embodiment, when the protection IC 101 receives information S indicating that a discharging current is flowing when the charge control transistor TR1 is in the off state or information S indicating that a charging current is flowing when the discharge control transistor TR2 is in the off state from the fuel gauge IC 701, the protection IC 101 turns on the transistor, thereby suppressing heat generation in the transistor when the protection IC 101 returns from the protection state.

[0081] The protection IC 101 and the fuel gauge IC 701 detect the current I flowing through the secondary battery 210 by monitoring the voltage generated across the resistor element Rsns. The protection IC 101 detects an overcurrent flowing through the secondary battery 210 by monitoring the voltage generated across the resistor element Rsns via terminals CS and VP. Meanwhile, the fuel gauge IC 701 detects a minute current value that is sufficiently smaller than the overcurrent flowing through the secondary battery 210 by monitoring the voltage generated across the resistor element Rsns via terminals IN1 and IN2. The fuel gauge IC 701 detects the current I with a lower resolution than the protection IC 101 in order to calculate the remaining capacity of the secondary battery 210 with high accuracy.

[0082] The fuel gauge IC 701 has a resolution capable of detecting minute currents I, so it can quickly detect the start of a discharge current Idis flowing when a load is connected in the overcharge protection state, or the start of a charge current Ichg flowing when a charger is connected in the overdischarge protection state. As a result, when the current I starts to flow through the parasitic diode while the charge control transistor TR1 or the discharge control transistor TR2 is off, the fuel gauge IC 701 can quickly transmit information S that the current I is flowing. As a result, the time that the current I flows through the parasitic diode is shortened, thereby suppressing heat generation in the charge control transistor TR1 or the discharge control transistor TR2.

[0083] 6 is a diagram showing an example of the configuration of the protection circuit according to the first embodiment. The protection IC 101 has an input circuit 225, a state detection circuit 226, a detection circuit 222, and a control circuit 221. The input circuit 225 or the state detection circuit 226 may be included in the detection circuit 222. The control circuit 221 has a charge control circuit 221a and a discharge control circuit 221b.

[0084] The input circuit 225 makes the discharge current detection signal Sd active (high level in this example) and makes the charge current detection signal Sc inactive (low level in this example) when it receives information S that a discharge current is flowing through the secondary battery 210. The input circuit 225 makes the discharge current detection signal Sd inactive (low level in this example) and makes the charge current detection signal Sc active (high level in this example) when it receives information S that a charge current is flowing through the secondary battery 210.

[0085] When the potential of terminal VP is lower than the status detection threshold (=potential of terminal VDD−predetermined voltage VREF2), the status detection circuit 226 determines that a load is connected to terminals P+ and P− and that discharging has commenced for the secondary battery 210. In this case, the status detection circuit 226 sets the load connection signal Sa to active (high level in this example) and the charger connection signal Sb to inactive (low level in this example).

[0086] When the potential of terminal VP is higher than the status detection threshold (=potential of terminal VDD−predetermined voltage VREF2), the status detection circuit 226 determines that a charger is connected to terminals P+ and P− and that charging has commenced for the secondary battery 210. In this case, the status detection circuit 226 sets the load connection signal Sa to an inactive state (low level in this example) and sets the charger connection signal Sb to an active state (high level in this example).

[0087] The detection circuit 222 generates an overcharge detection signal VD1 and an overcharge recovery signal VR1 by comparing two divided voltages of the power supply voltage Vdd with a reference voltage VREF1. When the power supply voltage Vdd is higher than a predetermined overcharge detection voltage Vdet1, the detection circuit 222 makes the overcharge detection signal VD1 active (high level in this example) and makes the overcharge recovery signal VR1 inactive (low level in this example). When the power supply voltage Vdd is lower than the predetermined overcharge recovery voltage Vrel1, the detection circuit 222 makes the overcharge recovery signal VR1 active (high level in this example) and makes the overcharge detection signal VD1 inactive (low level in this example).

[0088] The detection circuit 222 generates an over-discharge detection signal VD2 and an over-discharge recovery signal VR2 by comparing two divided voltages of the power supply voltage Vdd with a reference voltage VREF1. When the power supply voltage Vdd is lower than a predetermined over-discharge detection voltage Vdet2, the detection circuit 222 makes the over-discharge detection signal VD2 active (high level in this example) and makes the over-discharge recovery signal VR2 inactive (low level in this example). When the power supply voltage Vdd is higher than the predetermined over-discharge recovery voltage Vrel2, the detection circuit 222 makes the over-discharge recovery signal VR2 active (high level in this example) and makes the over-discharge detection signal VD2 inactive (low level in this example).

[0089] The charge control circuit 221 a includes delay circuits 41 and 42 , AND gates 23 and 24 , and an RS flip-flop 25 .

[0090] When the active overcharge detection signal VD1 continues for the detection delay time tVdet1, the delay circuit 41 switches the level of its output signal from inactive (low level in this example) to active (high level in this example). The AND gate 23 receives the output signal of the delay circuit 41 and the inverted output signal QB1 of the RS flip-flop 25 and outputs the logical product thereof. The output signal of the AND gate 23 is input to the set terminal S1 of the RS flip-flop 25.

[0091] When the active overcharge recovery signal VR1 continues for the recovery delay time tVrel1, the delay circuit 42 switches the level of its output signal from inactive (low level in this example) to active (high level in this example). The AND gate 24 receives the output signal of the delay circuit 42, the output signal Q1 of the RS flip-flop 25, and the load connection signal Sa of the state detection circuit 226, and outputs the logical product thereof. The output signal of the AND gate 24 is input to the OR gate G1.

[0092] The OR gate G1 receives the output signal of the AND gate 24 and the discharge current detection signal Sd of the input circuit 225 and outputs the logical sum thereof. The output signal of the OR gate G1 is input to the reset terminal R1 of the RS flip-flop 25. The logical level of the output signal Q1 of the RS flip-flop 25 is inverted by the inverter circuit 21, and the inverted signal is output from the terminal COUT as a gate control signal.

[0093] The discharge control circuit 221b includes delay circuits 43 and 44, AND gates 26 and 27, and an RS flip-flop 28.

[0094] When the active over-discharge detection signal VD2 continues for the detection delay time tVdet2, the delay circuit 43 switches the level of its output signal from inactive (low level in this example) to active (high level in this example). The AND gate 26 receives the output signal of the delay circuit 43 and the inverted output signal QB2 of the RS flip-flop 28, and outputs the logical product of these. The output signal of the AND gate 26 is input to the set terminal S2 of the RS flip-flop 28.

[0095] When the active overdischarge recovery signal VR2 continues for the recovery delay time tVrel2, the delay circuit 44 switches the level of its output signal from inactive (low level in this example) to active (high level in this example). The AND gate 27 receives the output signal of the delay circuit 44, the output signal Q2 of the RS flip-flop 28, and the charger connection signal Sb of the state detection circuit 226, and outputs the logical AND of these. The output signal of the AND gate 27 is input to the OR gate G2.

[0096] The output signal of the AND gate 27 and the charging current detection signal Sc of the input circuit 225 are input to the OR gate G2, which outputs the logical sum thereof. The output signal of the OR gate G2 is input to the reset terminal R2 of the RS flip-flop 28. The logical level of the output signal Q2 of the RS flip-flop 28 is inverted by the inverter circuit 22, and the inverted signal is output from the terminal DOUT as a gate control signal.

[0097] 7 is a timing chart showing an example of the operation of the protection circuit according to the first embodiment when it recovers from the overcharge protection state. In FIG. 7, "first comparative embodiment" refers to a configuration in which information S is not transmitted or received as in FIG. 2, and "first embodiment" refers to the configuration shown in FIG. 6.

[0098] As shown in FIG. 7 , according to the circuit configuration of FIG. 6 , at time T1, the power supply voltage Vdd becomes higher than the overcharge detection voltage Vdet1, causing the overcharge detection signal VD1 to change from low to high. If the power supply voltage Vdd remains higher than the overcharge detection voltage Vdet1 for the detection delay time tVdet1, the output signal Q1 of the RS flip-flop 25 changes from low to high (time T2). This causes the charge control transistor TR1 to change from on to off. Then, at time T3, discharge begins, and the protection IC 101 receives information S from the fuel gauge IC 701 indicating that a discharge current is flowing. Then, circuit operation or arithmetic processing, such as the input circuit 225, is performed. At time T4, after a predetermined time has elapsed, the reset terminal R1 of the RS flip-flop 25 becomes active, causing the output signal Q1 to change from high to low. This causes the charge control transistor TR1 to change from off to on. Therefore, the current flowing through the parasitic diode D1 of the charge control transistor TR1 is shorter than in the first comparative example, and heat generation in the charge control transistor TR1 is suppressed.

[0099] 8 is a timing chart showing an example of the operation when the protection circuit according to the first embodiment recovers from the over-discharge protection state. In FIG. 7, "first comparative embodiment" refers to a configuration in which information S is not transmitted or received as in FIG. 4, and "first embodiment" refers to the configuration shown in FIG.

[0100] As shown in FIG. 8 , according to the circuit configuration of FIG. 6 , at time T5, the power supply voltage Vdd becomes lower than the overdischarge detection voltage Vdet2, causing the overdischarge detection signal VD2 to change from low to high. If the power supply voltage Vdd remains lower than the overdischarge detection voltage Vdet2 for the detection delay time tVdet2, the output signal Q2 of the RS flip-flop 28 changes from low to high (time T6). This causes the discharge control transistor TR2 to change from on to off. Then, at time T7, charging begins, and the protection IC 101 receives information S indicating that a charging current is flowing from the fuel gauge IC 701. Then, circuit operation or arithmetic processing, such as the input circuit 225, is performed. At time T8, after a predetermined time has elapsed, the reset terminal R2 of the RS flip-flop 28 becomes active, causing the output signal Q2 to change from high to low. This causes the discharge control transistor TR2 to change from off to on. Therefore, the current flowing through the parasitic diode D2 of the discharge control transistor TR2 is shorter than in the first comparative example, and heat generation in the discharge control transistor TR2 is suppressed.

[0101] 9 is a circuit block diagram showing an example of a system including a protection circuit according to the second embodiment. In the second embodiment, the same configurations, actions, and effects as those of the above-described embodiments will not be described again by citing the above descriptions. The second embodiment differs from the first embodiment in that a switch circuit 203 is provided on the low-side ground line 202.

[0102] The system 502 shown in FIG. 9 includes a battery device 402 and an electronic device 300. The system 502 may also include a charger 302 that charges the battery device 402. The battery device 402 is an example of a power supply system that supplies power to the electronic device 300. The battery device 402 includes a secondary battery 210 and a battery monitoring device 602. The battery monitoring device 602 is an example of a battery monitoring module that monitors the secondary battery 210. The battery monitoring device 602 is a component that includes, for example, a board on which at least a protection IC 102 or a fuel gauge IC 701 is mounted. The protection IC 102 is an example of a protection circuit used to protect a secondary battery. The protection IC 102 includes, for example, a charge control terminal (terminal COUT), a discharge control terminal (terminal DOUT), a power supply terminal (terminal VDD), a ground terminal (terminal VSS), a current detection terminal (terminal CS), a monitoring terminal (terminal VM), and a receiving terminal (terminal RX). The terminal VM has a function similar to that of the terminal VP in the first embodiment. The protection IC 102 includes a detection circuit 222 and a control circuit 221 .

[0103] The detection circuit 222 detects a charging overcurrent of the secondary battery 210 by monitoring the potential difference ΔV2 between the terminals CS and VM. The detection circuit 222 compares the potential difference ΔV2 with a predetermined charging overcurrent detection voltage Vdet4, and when the potential difference ΔV2 is lower than the charging overcurrent detection voltage Vdet4 with respect to the terminal CS, the detection circuit 222 generates a charging overcurrent detection signal indicating that a charging overcurrent of the secondary battery 210 has been detected. In other words, the detection circuit 222 generates the charging overcurrent detection signal when the voltage of the terminal VM is lower than the charging overcurrent detection voltage Vdet4 with respect to the terminal CS.

[0104] The detection circuit 222 compares the potential of the terminal VM with a state detection threshold that is higher than the potential of the terminal VSS, and when the potential of the terminal VM is higher than the state detection threshold, generates a load connection signal that indicates a state in which a load such as the electronic device 300 is connected to the terminal P−. This is because when a load such as the electronic device 300 is connected to the terminals P+ and P−, the potential of the terminal VM rises, increasing the potential difference between the terminals VSS and VM.

[0105] The detection circuit 222 detects a discharge overcurrent of the secondary battery 210 by monitoring the potential difference ΔV2 between terminals CS and VM. The detection circuit 222 compares the potential difference ΔV2 with a predetermined discharge overcurrent detection voltage Vdet3, and when the potential difference ΔV2 is higher than the discharge overcurrent detection voltage Vdet3 with respect to terminal CS, the detection circuit 222 generates a discharge overcurrent detection signal indicating that a discharge overcurrent of the secondary battery 210 has been detected. In other words, the detection circuit 222 generates a discharge overcurrent detection signal when the voltage of terminal VM is higher than the discharge overcurrent detection voltage Vdet3 with respect to terminal CS.

[0106] The detection circuit 222 compares the potential of the terminal VM with a state detection threshold that is higher than the potential of the terminal VSS, and when the potential of the terminal VM is lower than the state detection threshold, generates a charger connection signal that indicates a state in which the charger 302 is electrically connected to the terminal P-. This is because when the charger 302 is electrically connected to the terminals P+ and P-, the potential of the terminal VM drops, and the potential difference between the terminals VSS and VM becomes smaller.

[0107] When the potential of terminal IN2 is lower than the potential of terminal IN1, the fuel gauge IC 701 determines that the current I is a charging current of the secondary battery 210, and when the potential of terminal IN2 is higher than the potential of terminal IN1, the fuel gauge IC 701 determines that the current I is a discharging current of the secondary battery 210.

[0108] Resistive element Rsns is provided on ground line 202 between transistors TR1, TR2 and terminal P-. As a result, even if an abnormal current path occurs between terminal IN1 and terminal A or the like due to a malfunction of fuel gauge IC 701, causing an overcurrent to flow, overcurrent protection by protection IC 101 will function, improving the reliability of battery monitoring device 602.

[0109] Next, an example of the operation when the protection circuit recovers from the overcharge protection state will be described.

[0110] FIG. 10 is a diagram showing an example of the operation of the protection circuit according to the second embodiment when it recovers from an overcharge protection state. The vertical axis of FIG. 10 represents voltage, and the horizontal axis represents time. The solid line represents the voltage at terminal P-, and the dotted line represents the voltage at terminal B-. When the charge control transistor TR1 is turned off due to overcharge detection (overcharge protection state), and a load is connected to terminals P+ and P-, the discharge current Idis is detected by the fuel gauge IC 701. The occurrence of the discharge current Idis is detected, for example, when the voltage at terminal IN2 becomes higher than the voltage at terminal IN1. In the overcharge protection state, the protection IC 102 continues to turn off the charge control transistor TR1 until it receives information S from the fuel gauge IC 701 indicating that the discharge current Idis is flowing. Here, the discharge current Idis is detected earlier than the time it takes for the power supply voltage Vdd to drop below the overcharge recovery voltage Vrel1. This is because the discharge current Idis flows through the parasitic diode D1 for a certain period of time, causing the power supply voltage Vdd to drop below the overcharge recovery voltage Vrel1.

[0111] When the protection IC 102 receives information S from the fuel gauge IC 701 indicating that a discharge current Idis is flowing in the overcharge protection state, it switches the charge control transistor TR1 from off to on, even if the power supply voltage Vdd has not dropped below the overcharge recovery voltage Vrel1. Note that there may be a predetermined delay due to the circuit operation of the protection IC 102 between receiving the information S and turning on the charge control transistor TR1. However, even including this delay, the timing at which the charge control transistor TR1 turns on upon detection of the discharge current Idis is earlier than the timing at which the charge control transistor TR1 turns on upon detection of the power supply voltage Vdd below the overcharge recovery voltage Vrel1. Therefore, when the protection IC 102 recovers from the overcharge protection state, the time during which the discharge current Idis flows through the parasitic diode D1 of the charge control transistor TR1 is shortened, thereby suppressing heat generation in the charge control transistor TR1. Suppressing heat generation in the charge control transistor TR1 improves the reliability of the charge control transistor TR1.

[0112] When the charge control transistor TR1 is in the off state, the state in which the discharge current Idis flows through the parasitic diode D1 of the charge control transistor TR1 is referred to as a diode conduction state. The potential difference between terminals P- and B- is larger when the parasitic diode D1 is in the diode conduction state than when the charge control transistor TR1 is in the on state. Therefore, the fuel gauge IC 701 may, for example, measure the potential difference between terminals P- and B-, and when the measured value is higher than when the charge control transistor TR1 is in the on state, detect that the discharge current Idis is flowing through the parasitic diode D1 of the charge control transistor TR1. When the fuel gauge IC 701 detects that the discharge current Idis is flowing through the parasitic diode D1 of the charge control transistor TR1, it may transmit information S indicating that the discharge current Idis is flowing.

[0113] Next, an example of the operation when the protection circuit recovers from the over-discharge protection state will be described.

[0114] FIG. 11 is a diagram illustrating an example of the operation of the protection circuit according to the second embodiment when it recovers from an overdischarge protection state. The vertical axis of FIG. 11 represents voltage, and the horizontal axis represents time. The solid line represents the voltage at terminal P-, and the dotted line represents the voltage at terminal B-. When the discharge control transistor TR2 is turned off due to overdischarge detection (overdischarge protection state), and the charger 302 is connected to terminals P+ and P-, the charging current Ichg is detected by the fuel gauge IC 701. The generation of the charging current Ichg is detected, for example, when the voltage at terminal IN2 becomes lower than the voltage at terminal IN1. In the overdischarge protection state, the protection IC 101 continues to turn off the discharge control transistor TR2 until it receives information S from the fuel gauge IC 701 indicating that the charging current Ichg is flowing. Here, the charging current Ichg is detected earlier than the time it takes for the power supply voltage Vdd to rise above the overdischarge recovery voltage Vrel2. This is because the charging current Ichg flows through the parasitic diode D2 for a certain period of time, causing the power supply voltage Vdd to rise above the over-discharge recovery voltage Vrel2.

[0115] When the protection IC 102 receives information S from the fuel gauge IC 701 indicating that the charging current Ichg is flowing in the over-discharge protection state, it switches the discharge control transistor TR2 from off to on, even if the power supply voltage Vdd has not yet risen above the over-discharge recovery voltage Vrel2. Note that there may be a predetermined delay due to the circuit operation of the protection IC 102 between receiving the information S and turning on the discharge control transistor TR2. However, even including this delay, the timing at which the discharge control transistor TR2 turns on upon detection of the charging current Ichg is earlier than the timing at which the discharge control transistor TR2 turns on upon detection of the power supply voltage Vdd equal to or greater than the over-discharge recovery voltage Vrel2. Therefore, when the protection IC 102 recovers from the over-discharge protection state, the time during which the charging current Ichg flows through the parasitic diode D2 of the discharge control transistor TR2 is shortened, thereby suppressing heat generation in the discharge control transistor TR2. Suppressing heat generation in the discharge control transistor TR2 improves the reliability of the discharge control transistor TR2.

[0116] When the discharge control transistor TR2 is in the off state, the state in which the charging current Ichg flows through the parasitic diode D2 of the discharge control transistor TR2 is referred to as a diode conduction state. The potential difference between terminals P- and B- is larger when the parasitic diode D2 is in the diode conduction state than when the discharge control transistor TR2 is in the on state. Therefore, the fuel gauge IC 701 may, for example, measure the potential difference between terminals P- and B-, and when the measured value is higher than when the discharge control transistor TR2 is in the on state, detect that the charging current Ichg is flowing through the parasitic diode D2 of the discharge control transistor TR2. When the fuel gauge IC 701 detects that the charging current Ichg is flowing through the parasitic diode D2 of the discharge control transistor TR2, it may transmit information S indicating that the charging current Ichg is flowing.

[0117] In this way, in the second embodiment, when the protection IC 102 receives information S from the fuel gauge IC 701 indicating that a discharging current is flowing when the charge control transistor TR1 is in the off state or information S indicating that a charging current is flowing when the discharge control transistor TR2 is in the off state, the protection IC 102 turns on the transistor. This suppresses heat generation in the transistor when the protection IC 102 returns from the protection state.

[0118] 12 is a diagram showing an example of the configuration of a protection circuit according to the second embodiment. The protection IC 102 has an input circuit 225, a state detection circuit 226, a detection circuit 222, and a control circuit 221. The input circuit 225 or the state detection circuit 226 may be included in the detection circuit 222. The control circuit 221 has a charge control circuit 221a and a discharge control circuit 221b.

[0119] When the potential of the terminal VM is higher than the state detection threshold (= the potential of the terminal VSS + the predetermined voltage VREF2), the state detection circuit 226 determines that a load is connected to the terminals P+ and P- and that discharging has commenced for the secondary battery 210. In this case, the state detection circuit 226 sets the load connection signal Sa to active (high level in this example) and sets the charger connection signal Sb to inactive (low level in this example).

[0120] When the potential of terminal VM is lower than the state detection threshold (=potential of terminal VSS+predetermined voltage VREF2), the state detection circuit 226 determines that the charger is connected to terminals P+ and P- and that charging has commenced for the secondary battery 210. In this case, the state detection circuit 226 sets the load connection signal Sa to an inactive state (low level in this example) and sets the charger connection signal Sb to an active state (high level in this example).

[0121] The remaining configuration can be the same as the configuration of the first embodiment in Fig. 6. According to the circuit configuration in Fig. 12, heat generation in the charge control transistor TR1 or the discharge control transistor TR2 is suppressed, similar to the circuit configuration in Fig. 6.

[0122] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0123] For example, the positions of the charge control transistor TR1 and the discharge control transistor TR2 may be interchanged with each other with respect to the positions shown in the figure. The switch circuit 203 may be built into the protection IC.

[0124] Fig. 13 is a circuit block diagram showing a modified example of a system including a protection circuit according to the first embodiment. The battery device 401 shown in Fig. 13 differs from the battery device 401 shown in Fig. 1 in that the protection IC 101 and the fuel gauge IC 701 shown in Fig. 1 are replaced with a fuel gauge built-in protection IC 801 that combines the protection IC 101 and the fuel gauge IC 701 into a single IC.

[0125] The fuel gauge built-in protection IC 801 includes terminals COUT, DOUT, VDD, VSS, VP, IN1, and IN2. These terminals are, for example, external connection terminals for connecting the internal circuit of the fuel gauge built-in protection IC 801 to the outside of the fuel gauge built-in protection IC 801.

[0126] The fuel gauge built-in protection IC 801 includes a protection circuit 811 and a fuel gauge circuit 871. The protection circuit 811 has the same function as the protection IC 101 and operates on the power supply voltage Vdd applied between terminals VDD and VSS. The fuel gauge circuit 871 has the same function as the fuel gauge IC 701 and operates on the power supply voltage applied between terminals VP and VSS.

[0127] By combining the protection IC 101 and fuel gauge IC 701 shown in FIG. 1 into a single fuel gauge built-in protection IC 801, the terminal VP of the protection IC 101 and the terminal BAT of the fuel gauge IC 701 can be made common to the terminal VP shown in FIG. 13. By combining the protection IC 101 and fuel gauge IC 701 shown in FIG. 1 into a single fuel gauge built-in protection IC 801, the terminal CS of the protection IC 101 and the terminal IN1 of the fuel gauge IC 701 can be made common to the terminal IN1 shown in FIG. 13. By combining multiple terminals into a single common terminal in this way, the number of terminals of the fuel gauge built-in protection IC 801 can be reduced. As a result, the fuel gauge built-in protection IC 801, the battery monitoring device 601, and the battery device 401 can be made smaller, and ultimately the system 501 can be made smaller.

[0128] The multiple chips mounted on the fuel gauge built-in protection IC 801 (the chip on which the protection circuit 811 is mounted and the chip on which the fuel gauge circuit 871 is mounted) can be integrated into a single chip. This allows the information S to be shared within a single chip, making it possible to omit the terminal RX of the protection IC 101 and the terminal TX of the fuel gauge IC 701. As a result, the fuel gauge built-in protection IC 801, the battery monitoring device 601, and the battery device 401 can be made smaller, and ultimately the system 501 can be made smaller.

[0129] The fuel gauge circuit 871 has an ADC (Analog-Digital Converter) 223 to accurately calculate the remaining capacity of the secondary battery 210. The fuel gauge circuit 871 can accurately calculate (measure) the output voltage of the battery device 401, which is the voltage between terminals P+ and P-, by monitoring the voltage between terminals VP and VSS using the ADC 223. The fuel gauge circuit 871 can also accurately calculate (measure) the elemental voltage of the secondary battery 210, which is the voltage between terminals B+ and B-, by monitoring the voltage between terminals VDD and VSS using the ADC 223. The fuel gauge circuit 871 can calculate the wiring impedance, including the resistance value of the resistive element Rsns, by using these two measured voltage values ​​and the value of the detected current I. The fuel gauge circuit 871 transmits the calculated value of this wiring impedance to the PMIC 303 from terminal A, thereby enabling the PMIC 303 to operate in an appropriate state (for example, to appropriately control the charging current to the secondary battery 210).

[0130] Fig. 14 is a circuit block diagram showing a modified example of a system including a protection circuit according to the second embodiment. The battery device 402 shown in Fig. 14 differs from the battery device 402 shown in Fig. 9 in that the protection IC 102 and the fuel gauge IC 701 shown in Fig. 9 are replaced with a fuel gauge built-in protection IC 802 that combines the protection IC 102 and the fuel gauge IC 701 into a single IC.

[0131] The fuel gauge built-in protection IC 802 includes terminals COUT, DOUT, VDD, VSS, VM, IN1, and IN2. These terminals are, for example, external connection terminals for connecting the internal circuit of the fuel gauge built-in protection IC 802 to the outside of the fuel gauge built-in protection IC 802.

[0132] The fuel gauge built-in protection IC 802 includes a protection circuit 812 and a fuel gauge circuit 871. The protection circuit 812 has the same function as the protection IC 102 and operates on the power supply voltage Vdd applied between terminals VDD and VSS. The fuel gauge circuit 871 has the same function as the fuel gauge IC 701 and operates on the power supply voltage applied between terminals VM and VDD.

[0133] By combining the protection IC 102 and fuel gauge IC 701 shown in FIG. 9 into a single fuel gauge built-in protection IC 802, the terminal VM of the protection IC 102 and the terminal GND of the fuel gauge IC 701 can be made common to the terminal VM shown in FIG. 14. By combining the protection IC 102 and fuel gauge IC 701 shown in FIG. 9 into a single fuel gauge built-in protection IC 802, the terminal CS of the protection IC 102 and the terminal IN1 of the fuel gauge IC 701 can be made common to the terminal IN1 shown in FIG. 14. By combining multiple terminals into a single common terminal in this way, the number of terminals of the fuel gauge built-in protection IC 802 can be reduced. As a result, the fuel gauge built-in protection IC 802, the battery monitoring device 602, and the battery device 402 can be made smaller, and ultimately the system 502 can be made smaller.

[0134] The multiple chips mounted on the fuel gauge built-in protection IC 802 (the chip on which the protection circuit 812 is mounted and the chip on which the fuel gauge circuit 871 is mounted) can be integrated into a single chip. This allows the information S to be shared within a single chip, making it possible to omit the terminal RX of the protection IC 102 and the terminal TX of the fuel gauge IC 701. As a result, the fuel gauge built-in protection IC 802, the battery monitoring device 602, and the battery device 402 can be made smaller, and ultimately the system 502 can be made smaller.

[0135] The fuel gauge circuit 871 includes an ADC 223 for accurately calculating the remaining capacity of the secondary battery 210. By monitoring the voltage between terminals VM and VDD using the ADC 223, the fuel gauge circuit 871 can accurately calculate (measure) the output voltage of the battery device 402, which is the voltage between terminals P+ and P-. By monitoring the voltage between terminals VDD and VSS using the ADC 223, the fuel gauge circuit 871 can accurately calculate (measure) the raw voltage of the secondary battery 210, which is the voltage between terminals B+ and B-. By using these two measured voltage values ​​and the detected current I, the fuel gauge circuit 871 can calculate the wiring impedance, including the resistance value of the resistive element Rsns. By transmitting this calculated wiring impedance value from terminal A to the PMIC 303, the fuel gauge circuit 871 can operate the PMIC 303 in an appropriate state (e.g., appropriately control the charging current to the secondary battery 210).

[0136] This international application claims priority based on Japanese Patent Application No. 2024-018457, filed on February 9, 2024, the entire contents of which are incorporated herein by reference.

[0137] 41, 42, 43, 44 Delay circuit 101, 102 Protection IC 201 Power supply line 202 Ground line 203 Switch circuit 210 Secondary battery 211 Positive electrode 212 Negative electrode 221 Control circuit 221a Charging control circuit 221b Discharging control circuit 222 Detection circuit 223 ADC 225 Input circuit 226 Status detection circuit 300 Electronic device 302 Charger 303 PMIC 304 Internal circuit 305 Connector 401, 402 Battery device 501, 502 System 601, 602 Battery monitoring device 701 Fuel gauge IC 801, 802 Fuel gauge built-in protection IC 811, 812 Protection circuit 871 Fuel gauge circuit TR1 Charging control transistor TR2 Discharging control transistor

Claims

1. A battery monitoring module comprising: a protection circuit that detects overcharging or over-discharging of a secondary battery; a monitoring circuit that monitors the current flowing in the secondary battery and transmits information about the current flow; and a transistor that is turned on or off by the protection circuit and controls the current, wherein the protection circuit turns on the transistor when it receives the information while the transistor is off.

2. The battery monitoring module according to claim 1, wherein the monitoring circuit has a terminal for transmitting the information, and the protection circuit has a terminal for receiving the information.

3. The battery monitoring module according to claim 1, wherein the protection circuit turns off the transistor when it detects over-discharge of the secondary battery, and keeps the transistor turned off until it receives the information.

4. The battery monitoring module according to claim 1, wherein the protection circuit turns off the transistor when it detects overcharging of the secondary battery, and keeps the transistor turned off until it receives the information.

5. A battery monitoring module as described in claim 1, further comprising: a first positive terminal and a first negative terminal for connecting a load; a second positive terminal and a second negative terminal for connecting the secondary battery; and a resistor for detecting current in the monitoring circuit, wherein the resistor is provided in the first current path between the transistor and the first positive terminal when the current path in which the transistor is provided is a first current path connecting the first positive terminal and the second positive terminal, and is provided in the second current path between the transistor and the first negative terminal when the current path in which the transistor is provided is a second current path connecting the first negative terminal and the second negative terminal.

6. The battery monitoring module of claim 5, wherein when a state in which the current flows through the parasitic diode of the transistor when the transistor is in an off state is defined as a diode conduction state, if the current path in which the transistor is provided is the first current path, the potential difference between the first positive terminal and the second positive terminal is larger in the diode conduction state than in the on state of the transistor, and if the current path in which the transistor is provided is the second current path, the potential difference between the first negative terminal and the second negative terminal is larger in the diode conduction state than in the on state of the transistor.

7. The battery monitoring module according to claim 5, wherein the protection circuit and the monitoring circuit detect the current by monitoring the voltage generated across the resistor, and the monitoring circuit detects the current with a resolution smaller than that of the protection circuit.

8. A battery monitoring module according to any one of claims 1 to 7, wherein the transistor includes a first transistor and a second transistor connected in series, and the protection circuit turns on the first transistor when it receives the information while the first transistor is in an off state and the second transistor is in an on state.

9. A battery monitoring module as described in claim 8, wherein the first transistor is a charge control transistor capable of cutting off a charging current of the secondary battery, the second transistor is a discharge control transistor capable of cutting off a discharging current of the secondary battery, and the protection circuit turns on the charge control transistor when it receives information that the discharging current is flowing when the charge control transistor is in an off state, or turns on the discharge control transistor when it receives information that the charging current is flowing when the discharge control transistor is in an off state.

10. A power supply system comprising: a secondary battery; a protection circuit that detects overcharging or over-discharging of the secondary battery; a monitoring circuit that monitors a current flowing through the secondary battery and transmits information about the current flow; and a transistor that is turned on or off by the protection circuit to control the current, wherein the protection circuit turns on the transistor when it receives the information while the transistor is in an off state.

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