A disconnection detection circuit

Abstract

The invention discloses a disconnection detection circuit, comprising a power switching circuit, B1-Bn disconnection detection subunits and a lowest battery BAT1 disconnection detection control circuit; the input end of the power switching circuit is connected to a chip pin Vcn and a chip pin Vcn-1, the output end of the power switching circuit is connected to a power source VDD, the power switching circuit is used for providing the power source VDD from a second highest battery BATn-1 when an open circuit occurs between the chip pin Vcn and the highest battery BATn; the B1-Bn disconnection detection subunits are used for judging whether an open circuit occurs between a battery pack and a chip pin, and mainly comprise high-voltage current mirror tubes Mh2-Mhn and Me1-Me2, low-voltage current mirror tubes Ma1-Man and Mb2-Mbn and switch tubes Mf2-Mfn, Mg2-Mgn, Md1-Md3; the input end of the lowest battery BAT1 disconnection detection control circuit is connected to the output end of the B1 disconnection detection subunit, and is used for controlling the conduction and disconnection of the switch tube in the B1 disconnection detection subunit. The present invention solves the problem that the highest battery in a series-connected lithium battery pack cannot be detected when the battery is disconnected, thereby making the charging and discharging of the lithium battery pack safer and more reliable.

Description

Technical Field

[0001] The invention relates to the field of lithium battery disconnection detection, and in particular to a disconnection detection circuit. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high charging efficiency, low self-discharge rate, small size, light weight, and environmental protection. They have replaced cadmium nickel and zinc manganese batteries and are widely used in portable products such as smart phones and tablets. They also provide power sources for power tools, electric bicycles, electric vehicles, etc. Multi-cell lithium battery packs increase voltage and capacity by connecting single-cell lithium batteries in series / parallel to power devices with higher power. In order to ensure the safe operation of the battery pack, the battery pack must be equipped with a lithium battery protection board. The core of the lithium battery protection board is the lithium battery protection chip, which is used to monitor the voltage, charge and discharge current, and whether the line is broken for each battery. When the lithium battery is found to be in an abnormal state, the charge / discharge circuit is cut off to prevent the lithium battery from being damaged or causing other safety accidents due to excessive charge / discharge.

[0003] The disconnection detection circuit is an important component of a multi-cell lithium battery protection chip. Due to problems such as cold soldering during the production of lithium battery protection boards, an open circuit occurs between one or more cells in the lithium battery pack and the corresponding detection pins of the lithium battery protection chip. The voltage, current and other working conditions of these batteries cannot be detected promptly and accurately by the lithium battery protection chip. If these batteries are overcharged or over-discharged, the chip cannot properly protect the batteries, which can easily lead to battery damage or even fire and other safety accidents.

[0004] Many companies have proposed their own inventions for the disconnection detection circuit in the multi-cell lithium battery protection chip: for example, the disconnection detection circuit of the multi-cell protection board proposed in patent CN108008301A, whose working principle is to detect whether the battery is disconnected during the narrow pulse signal. When the j-th battery is disconnected and the falling edge of the narrow pulse signal arrives, the chip pin voltage Vcj corresponding to the battery can be pulled up to a high voltage by the current source inside the chip. This voltage is equal to the sum of the chip pin voltage corresponding to the j+1-th battery and the threshold voltage of the PMOS switch tube. It is judged that the j-th battery is disconnected, and a disconnection detection control signal is output. Another example is a battery connection disconnection protection device and protection system proposed in patent CN103825252A, whose working principle is: first preset the disconnection protection voltage of each battery, and when the battery voltage collected by the voltage collection circuit inside the chip is greater than the preset voltage value, it is considered that the battery is disconnected.

[0005] The disadvantages of the first disconnection detection scheme are as follows: (1) This scheme cannot detect whether the top battery is disconnected, because in this scheme, the power supply voltage of the chip is provided by the top battery. Once the top battery is disconnected, the chip loses power and cannot work. (2) This scheme also cannot detect whether the second-highest battery is disconnected. The voltage of the chip pin corresponding to the second-highest battery can only be pulled up to the power supply voltage vdd at most. According to the circuit topology of this scheme, if it is necessary to detect that the second-highest battery is disconnected, the voltage of the detection pin corresponding to the second-highest battery needs to be pulled up to vdd+V TH,PMOS The above is obviously impossible to achieve. (3) This scheme uses a periodic narrow pulse signal to detect whether the battery is disconnected. Its purpose is to reduce the average power consumption of the disconnection detection circuit. However, the narrow pulse signal invented by this scheme has a period of 32s, but the pulse width is only 500μs. If the chip pin voltage needs to be pulled up to the high voltage required for disconnection detection within 500μs, a large pull-up current is required. Assume that a 0.1μF filter capacitor is connected to the chip pin corresponding to each battery, and the voltage difference between the two ends of a battery in the battery pack is 4.25V, and the threshold voltage of the PMOS switch tube is 0.7V. If the battery is disconnected, the chip pin voltage corresponding to the battery needs to be pulled up to above 4.25V+0.7V within a narrow pulse width of 500μs. Therefore, the required pull-up current is Since the lithium battery protection chip is a low-power chip, its internal reference current is generally in the order of nA. If a current of 1mA is to be generated, it needs to be obtained by mirroring through a large-size current mirror circuit, which will occupy a large chip area. (4) This solution cannot effectively protect the battery in a timely manner when the battery is disconnected and the falling edge of the narrow pulse signal has not arrived, which can easily cause damage to the battery. This solution only detects disconnection when the falling edge of the narrow pulse signal arrives. In order to reduce the power consumption of the disconnection detection circuit, the invented narrow pulse is required to have a large period and a small pulse width. If the battery in the battery pack is disconnected before the falling edge of the narrow pulse signal arrives, the chip will not be able to accurately detect the working status of the battery for a long time, making it impossible for the chip to correctly protect the battery and ensure the safety of the battery.

[0006] The disadvantages of the second disconnection detection scheme mentioned above are: (1) It cannot effectively distinguish between the overcharge (overdischarge) state of the battery and the disconnection state. This scheme compares the battery voltage detected by the voltage acquisition module in the chip with the preset disconnection protection voltage. If the detected battery voltage is greater than the preset value, it is determined that the battery is disconnected. However, when the battery in the battery pack is overcharged or overdischarged, the voltage collected by the voltage acquisition module may also be greater than the preset disconnection protection voltage. In this case, the chip will mistakenly judge the overcharge or overdischarge state of the battery as a disconnection. (2) The circuit structure is relatively complex, requiring the use of a large number of comparators to compare the battery voltage with the reference voltage, and requiring the invention of a complex reference voltage generation circuit, which will occupy a large chip area. (3) The battery voltage sampling circuit of the disconnection detection circuit is realized by dividing the battery voltage by resistors. Since the total voltage of the multi-cell lithium battery pack in the series state is relatively high, in order to reduce the current consumption on the voltage divider resistor, the voltage divider resistor needs to have a large resistance value, which will significantly increase the chip area. Summary of the invention

[0007] Therefore, it is necessary to provide a disconnection detection circuit to solve the problem that the existing disconnection detection circuit cannot effectively ensure the safety of the battery.

[0008] To achieve the above purpose, the inventor provides a disconnection detection circuit, including a power switching circuit, a reference voltage source VCC, and B2~Bn disconnection detection subunits; the input end of the power switching circuit is connected to the chip pin Vcn and the chip pin Vcn-1, and the output end of the power switching circuit is connected to the power supply VDD. The power switching circuit is used to provide the power supply VDD from the second highest battery BATn-1 when an open circuit occurs between the chip pin Vcn and the highest battery BATn. The B2~Bn disconnection detection subunits include high-voltage current mirror tubes Mh2~Mhn, low-voltage current mirror tubes Ma2~Man, low-voltage current mirror tubes Mb2~Mbn, high-voltage isolation tubes Mc2~Mcn, and switch tubes Mf2~Mfn, Mg2~Mgn. The source of the high-voltage current mirror tube Mhi is connected to the power supply VDD, the drain of the high-voltage current mirror tube Mhi is connected to the gate of the switch tube Mgi and the drain of the switch tube Mfi, the gate of the switch tube Mfi is connected to the chip pin Vci-1, and the source of the switch tube Mfi is connected to the chip pin Vci-1. The pin Vci is connected to the drain of the high-voltage isolation tube Mci, the gate of the high-voltage isolation tube Mci is connected to the reference voltage source VCC, the source of the high-voltage isolation tube Mci is connected to the drain of the low-voltage current mirror Mai, the source of the switch tube Mgi is connected to the reference voltage source VCC, the drain of the switch tube Mgi is connected to the drain of the low-voltage current mirror tube Mbi and an input end of the OR gate A1, the source of the low-voltage current mirror tube Mai and the source of the low-voltage current mirror tube Mbi are grounded, where 2≤i≤n, and the output signal of the OR gate A1 is the disconnection detection signal VBLD.

[0009] Furthermore, it also includes a B1 disconnection detection subunit, which includes a high-voltage current mirror tube Me1, a high-voltage current mirror tube Me2, a low-voltage current mirror tube Ma1, a high-voltage isolation tube Mc1, and switch tubes Md1, Md2, and Md3. The source electrodes of the high-voltage current mirror tube Me1 and the high-voltage current mirror tube Me2 are connected to the power supply VDD, the drain electrode of the high-voltage current mirror tube Me1 is connected to the source electrode of the switch tube Md2, the gate electrode of the switch tube Md2 and the gate electrode of the switch tube Md1 are connected to the output signal dn of the disconnection detection control circuit of the lowest battery BAT1, and the switch tube Md3 is connected to the output signal dn of the disconnection detection control circuit of the lowest battery BAT1. The drain of the tube Md2 is connected to the drain of the switch tube Md1, the gate of the switch tube Md3 and the chip pin Vc1, the source of the switch tube Md1 is connected to the drain of the high-voltage isolation tube Mc1, the gate of the high-voltage isolation tube Mc1 is connected to the reference voltage source VCC, the source of the high-voltage isolation tube Mc1 is connected to the drain of the low-voltage current mirror tube Ma1, the source of the low-voltage current mirror tube Ma1 and the source of the switch tube Md3 are grounded, and the drain of the switch tube Md3 is connected to the drain of the high-voltage current mirror tube Me2 and the input end out1 of the lowest battery BAT1 disconnection detection control circuit.

[0010] Furthermore, it also includes a lowest battery cell BAT1 disconnection detection control circuit, and the lowest battery cell BAT1 disconnection detection control circuit includes a D trigger A6, the D terminal of the D trigger A6 is grounded, the clk terminal of the D trigger A6 is connected to the output terminal of the delay circuit C2, the input terminal of the delay circuit C2 is connected to the input terminal out1 through the level conversion circuit C1, and the output terminal Q of the D trigger A6 is connected to the output signal dn through the level conversion circuit C3.

[0011] Furthermore, the lowest battery BAT1 disconnection detection control circuit comprises a NOR gate A4, a NOR gate A5, a D flip-flop A3 and an inverter A2, wherein the input end of the inverter A2 is connected to the out2 end, the output end of the inverter A2 is connected to the clk end of the D flip-flop A3, and the inverting output end of the D flip-flop A3 is connected to the inverting output end of the D flip-flop A3. The output terminal of the NOR gate A5 is connected to the set terminal of the D flip-flop A6, the other input terminal of the NOR gate A5 is connected to the output terminal of the NOR gate A4, and the input terminal of the NOR gate A4 is connected to the inverting output terminal of the D flip-flop A6. The output signal up is connected to the NOR gate A4, and the other input end is connected to the input end out1.

[0012] Furthermore, the power switching circuit includes a resistor R1, a diode D1 and a switch tube Mp1, the gate of the switch tube Mp1 is connected to one end of the resistor R1, the anode of the diode D1 and the chip pin Vcn, the source of the switch tube Mp1 is connected to the power supply voltage VDD and the cathode of the diode D1, the drain of the switch tube Mp1 is connected to the chip pin Vcn-1, and the other end of the resistor R1 is grounded.

[0013] Furthermore, it also includes a reference current source Ib, which is connected to the drain and gate of the low-voltage current mirror tube Ma0, the gates of the low-voltage current mirror tubes Ma1~Man and the gates of the low-voltage current mirror tubes Mb1~Mbn, and the source of the low-voltage current mirror tube Ma0 is grounded.

[0014] Furthermore, it also includes a low-voltage current mirror tube Mb1, the drain of the low-voltage current mirror tube Mb1 is connected to the source of the high-voltage isolation tube Mc0, the drain of the high-voltage isolation tube Mc0 is connected to the drain and gate of the high-voltage current mirror tube Me0, the gate of the high-voltage current mirror tube Me1, the gate of the high-voltage current mirror tube Me2 and the gates of the high-voltage current mirror tubes Mh2~Mhn, the gate of the high-voltage isolation tube Mc0 is connected to the reference voltage source VCC, and the source of the low-voltage current mirror tube Mb1 is grounded.

[0015] Different from the prior art, the above technical solution can detect whether the highest cell in the lithium battery pack is disconnected. When the highest cell is disconnected and the second highest cell is not disconnected, the power switching circuit in the disconnection detection circuit can switch the power supply voltage of the chip to the voltage provided by the second highest cell, maintaining the normal operation of the internal circuit of the chip, solving the problem of the highest cell disconnection in the series lithium battery pack that cannot be detected, making the charging and discharging of the lithium battery pack safer and more reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A line break detection circuit according to an embodiment of the present invention;

[0017] Figure 2 The figure is a schematic diagram of the changes of various signals when each battery cell in a battery pack is disconnected according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0019] See also Figure 1 to Figure 2, this embodiment provides a disconnection detection circuit, including a power switching circuit, a reference voltage source VCC, and B2~Bn disconnection detection subunits, where n is greater than or equal to 2. The input end of the power switching circuit is connected to the chip pin Vcn and the chip pin Vcn-1, and the output end of the power switching circuit is connected to the power supply VDD. The power switching circuit is used to provide the power supply VDD from the second highest battery BATn-1 when an open circuit occurs between the chip pin Vcn and the highest battery BATn. The B2~Bn disconnection detection subunits include high-voltage current mirror tubes Mh2~Mhn, low-voltage current mirror tubes Ma2~Man, low-voltage current mirror tubes Mb2~Mbn, high-voltage isolation tubes Mc2~Mcn, and switch tubes Mf2~Mfn, Mg2~Mgn. The source of the high-voltage current mirror tube Mhi is connected to the power supply VDD, the drain of the high-voltage current mirror tube Mhi is connected to the gate of the switch tube Mgi and the drain of the switch tube Mfi, the gate of the switch tube Mfi is connected to the chip pin Vci-1, the source of the switch tube Mfi is connected to the chip pin Vci and the drain of the high-voltage isolation tube Mci, the gate of the high-voltage isolation tube Mci is connected to the reference voltage source VCC, the source of the high-voltage isolation tube Mci is connected to the drain of the low-voltage current mirror tube Mai, the source of the switch tube Mgi is connected to the reference voltage source VCC, the drain of the switch tube Mgi is connected to the drain of the low-voltage current mirror tube Mbi and an input end of the OR gate A1, the source of the low-voltage current mirror tube Mai and the source of the low-voltage current mirror tube Mbi are grounded, where 2≤i≤n, and the output signal of the OR gate A1 is the disconnection detection signal VBLD.

[0020] The working principle of the above embodiment is as follows: Since the disconnection detection principle of the batteries BAT2 to BATn is the same, the working principle is described by taking the disconnection of the battery BAT2 as an example. When all batteries in the battery pack are normally connected to the battery disconnection detection circuit of the present invention, the voltage of the Vc2 pin is not affected by the pull-down current source ( Figure 1 The voltage of the Vc1 pin is lower than the voltage of the Vc2 pin, the gate-source voltage VGS2 of Mf2 is negative, Mf2 is in the off state, and the gate voltage of Mg2 is close to VDD, so that Mg2 is also in the off state, out2 is low level, and the disconnection detection output signal VBLD is low level. Regardless of whether the batteries BAT1 and BAT2 are overcharged or over-discharged, the voltage of the Vc1 pin is lower than the voltage of the Vc2 pin, and Mf2 will not be turned on, and the disconnection detection signal VBLD will not become a high level, so the overcharge or over-discharge of the battery will not be misjudged as a disconnection.

[0021] When an open circuit occurs between the battery BAT2 and the chip's Vc2 pin, the capacitor C2 connected to the Vc2 pin begins to pull down the current source ( Figure 1The low voltage current mirror tube Ma2 is discharged, and the voltage of Vc2 pin drops. When the voltage of Vc2 pin drops to Vc1-V TH,Mf2 Next, Mf2 is turned on, causing the gate voltage of Mg2 to drop, Mg2 is turned on, out2 becomes high level, and the disconnection detection signal VBLD changes from low level to high level. At the same time, VBLD is sent to the logic control module of the lithium battery protection chip. The logic control module controls the charging MOS and discharging MOS outside the chip to be turned off at the same time, cutting off the charging and discharging circuits of the multi-cell lithium battery protection board and entering the disconnection protection state.

[0022] In the above embodiment, the reference voltage source VCC is generated by a reference circuit inside the chip, and its voltage value is relatively small, mainly providing a power supply voltage for the low-voltage analog circuit inside the chip. Figure 1 The gates of the high-voltage NMOS tubes Mc0~Mcn in the circuit are connected to the reference voltage source VCC, the purpose of which is to isolate the low-voltage mirror current tube from the high voltage source VDD to ensure that the low-voltage circuit can work safely.

[0023] In the present invention, the disconnection detection principle of the lowest battery BAT1 cannot directly adopt the disconnection detection principle of the above-mentioned battery BAT2, because if the battery BAT1 adopts the same disconnection detection circuit as the battery BAT2, the gate of the NMOS switch connected to the Vc1 pin needs to be connected to VSS, and when the battery BAT1 is disconnected, the source voltage of the NMOS tube can only drop to VSS at the lowest, so the VGS of the NMOS switch tube can only be 0V at the maximum, and the NMOS switch tube cannot be turned on, resulting in an inability to determine whether the lowest battery is disconnected. If the gate of the NMOS switch tube is connected to a reference voltage higher than VSS, and the source is connected to the chip pin Vc1, when the battery BAT1 is disconnected, the voltage of the Vc1 pin will drop to below the reference voltage minus the threshold voltage of the NMOS switch tube, so that the disconnection detection signal VBLD changes from a low level to a high level. However, when the battery BAT1 is not disconnected but over-discharged, if the voltage at the Vc1 pin is just less than the reference voltage minus the threshold voltage of the NMOS switch tube, the disconnection detection signal VBLD will also change from a low level to a high level, so the over-discharge of the battery BAT1 will be mistakenly judged as a disconnection.

[0024] The disconnection detection circuit of the battery BAT1 includes a B1 disconnection detection subunit and a lowest-cell battery BAT1 disconnection detection control circuit, such as Figure 1The B1 line break detection subunit includes a high-voltage current mirror tube Me1, a high-voltage current mirror tube Me2, a low-voltage current mirror tube Ma1, a high-voltage isolation tube Mc1, and switch tubes Md1, Md2, and Md3. The sources of the high-voltage current mirror tubes Me1 and Me2 are connected to the power supply VDD, the drain of the high-voltage current mirror tube Me1 is connected to the source of the switch tube Md2, the gate of the switch tube Md2 is connected to the gate of the switch tube Md1 and the output signal dn of the disconnection detection control circuit of the lowest battery cell BAT1, the drain of the switch tube Md2 is connected to the drain of the switch tube Md1, the gate of the switch tube Md3 and the chip pin Vc1, the source of the switch tube Md1 is connected to the drain of the high-voltage isolation tube Mc1, the gate of the high-voltage isolation tube Mc1 is connected to the reference voltage source VCC, the source of the high-voltage isolation tube Mc1 is connected to the drain of the low-voltage current mirror tube Ma1, the source of the low-voltage current mirror tube Ma1 and the source of the switch tube Md3 are grounded, and the drain of the switch tube Md3 is connected to the drain of the high-voltage current mirror tube Me2 and the input end out1 of the disconnection detection control circuit of the lowest battery cell BAT1. The lowest battery BAT1 disconnection detection control circuit is used to receive the out1 signal and output a control signal dn to control the on and off of the switch tubes Md2 and Md1.

[0025] The disconnection detection principle adopted by the lowest battery BAT1 in the present invention is: when all batteries in the battery pack are not disconnected and the voltage of battery BAT1 is higher than the threshold voltage V TH,Md3 When the signal dn is high, Md1 is turned on, Md2 is turned off, and the pull-down current source ( Figure 1 The low-voltage current mirror tube Ma1 is turned on; when the battery BAT1 is over-discharged and the battery voltage is lower than the Md3 threshold voltage V TH,Md3 When the signal dn is low, Md1 is turned off, Md2 is turned on, and the pull-up current source ( Figure 1 In the figure, the high-voltage current mirror tube Me1 is turned on. Since the battery BAT1 is not disconnected, the voltage of the Vc1 pin will not be affected by the pull-down current source or the pull-up current source regardless of whether the battery BAT1 is overcharged or over-discharged, ensuring that the voltage of the Vc1 pin is always less than the voltage of the Vc2 pin, so that the switch Mf2 is always in the off state, out2 is always at a low level, and the disconnection detection output signal VBLD is also always kept at a low level, so the over-discharge or over-charge of the battery BAT1 will not be misjudged as a disconnection.

[0026] When only the battery BAT1 is disconnected, the capacitor C1 connected to the Vc1 pin begins to pull down the current source ( Figure 1 The current mirror tube Ma1 discharges, causing the voltage at the Vc1 pin to drop. When the voltage at the Vc1 pin drops to the threshold value V of Md3, TH,Md3When the voltage is below 0.05, Md3 is turned off, out1 changes from low level to high level, and out1 is sent to the lowest battery BAT1 disconnection detection control circuit, so that dn changes from high level to low level, so that Md1 is disconnected, Md2 is turned on, and the pull-up current source ( Figure 1 The current of the high-voltage current mirror tube Me1 starts to charge the capacitor C1, causing the voltage of the Vc1 pin to increase. When the voltage of the Vc1 pin rises to Vc2+V TH,Mf2 When the above, the switch Mf2 is turned on, the signal out2 changes from low level to high level, and the disconnection detection signal VBLD also changes from low level to high level, judging that the battery BAT1 is disconnected. At the same time, VBLD is sent to the logic control module of the lithium battery protection chip, and the logic control module controls the charging MOS and discharging MOS outside the chip to be turned off at the same time, cutting off the charging and discharging circuits of the multi-cell lithium battery protection board and entering the disconnection protection state.

[0027] As an optional embodiment of the disconnection detection control circuit of the lowest battery cell BAT1, the disconnection detection control circuit of the lowest battery cell BAT1 generates a control signal dn according to the change of the signal out1, thereby controlling the on and off of the switch tubes Md1 and Md2. The disconnection detection control circuit of the lowest battery cell BAT1 includes a D flip-flop A6, the D terminal of the D flip-flop A6 is grounded; the clk terminal of the D flip-flop is connected to the output terminal of the delay circuit C2, and the input terminal of the delay circuit C2 is connected to the input terminal out1 through the level conversion circuit C1; the set terminal of the D flip-flop A6 is connected to the output of the NOR gate A5, and one output terminal of the NOR gate A5 is connected to the inverting output terminal of the D flip-flop A3. The D terminal of D flip-flop A3 is grounded, the clk terminal of D flip-flop A3 is connected to the output terminal of inverter A2, the input terminal of inverter A2 is connected to out2, the other input terminal of NOR gate A5 is connected to the output terminal of NOR gate A4, one input terminal of NOR gate A4 is connected to the inverting output terminal of D flip-flop A6. The output of the D flip-flop A6 is connected to the input of the level conversion circuit C3, and the output signal of C3 is dn; the inverting ... The output signal is up.

[0028] The D flip-flop A6 and D flip-flop A3 adopt the rising edge trigger mode, and the set signal is low level effective. Under the initial condition, the set signal of D flip-flop A6 is low level, then the output terminal Q and The output signals of are high level and low level respectively, that is, the dn signal is high level under the initial condition.

[0029] When the lowest battery BAT1 is disconnected, the signal out1 will change from low level to high level, and the set signal of D flip-flop A6 will change from low level to high level. After a short delay, the clk signal of D flip-flop A6 will also change from low level to high level, and the dn signal will change from high level to low level, and the up signal will change from low level to high level. The set signal of D flip-flop will still remain high. When Vc1 is pulled up to Vc2+V TH,Mf2 When the voltage is above 10V, out2 changes from low level to high level, and the disconnection detection signal VBLD changes from low level to high level, judging that the battery BAT1 is disconnected. When the lowest battery BAT1 with disconnection is reconnected, out2 changes from high level to low level, and the signal at the clk terminal of the D flip-flop A3 changes from low level to high level, making the inverting output terminal of the D flip-flop A3 The signal of changes from low level to high level, and the set signal of D flip-flop A6 changes from high level to low level, so that the dn signal returns to high level and the up signal returns to low level.

[0030] In the battery BAT1 disconnection detection circuit, the lowest battery BAT1 disconnection detection control circuit and the B1 sub-detection unit are powered by different power supply voltages, wherein the lowest battery disconnection detection control circuit is powered by a low power reference voltage VCCD, and the reference voltage source VCCD is generated by a reference circuit inside the chip, and mainly provides a power supply voltage for the digital logic circuit inside the chip. The B1 sub-detection unit is powered by a high power supply voltage VDD. In order to ensure that the lowest battery disconnection detection voltage can work normally and safely, a level conversion circuit C1 that converts high voltage into low voltage is required, and converts the high-level signal of the output voltage of out1, which is VDD, into an outL signal with a high-level voltage of VCCD. At the same time, in order to ensure that the switch tubes Md1 and Md2 can be fully turned on and completely turned off, a level conversion circuit C3 that converts low voltage into high voltage is also required, and converts the high-level signal of the voltage VCCD output from the Q end of the D trigger A6 into a high-level signal with a voltage of VDD.

[0031] The power switching circuit is used to switch the power supply. There are many implementation methods. In some embodiments, the power switching circuit includes a resistor R1, a diode D1 and a switch tube Mp1. The gate of the switch tube Mp1 is connected to one end of the resistor R1, the positive electrode of the diode D1 and the chip pin Vcn. The source of the switch tube Mp1 is connected to the power supply voltage VDD and the negative electrode of the diode D1. The drain of the switch tube Mp1 is connected to the pin Vcn-1, and the other end of the resistor R1 is grounded. In this embodiment, when the battery BATn and BATn-1 are not disconnected, the internal power supply voltage VDD of the chip is equal to Vcn-V on,D1 , V on,D1is the forward conduction voltage of the diode, the gate-source voltage VGS of Mp1, Mp1>V TH,MP1 , Mp1 is turned off; when the battery BATn is disconnected and BATn-1 is not disconnected, the gate voltage of Mp1 is pulled down to ground by resistor R1, and Mp1 is turned on. The power supply VDD of the chip is supplied by Vcn-1; if the battery BATn is not disconnected and BATn-1 is disconnected, VDD is equal to Vcn-V on,D1 , the gate-source voltage VGS of Mp1,Mp1>V TH,Mp1 , then Mp1 is turned off. The reverse breakdown voltage of the high-voltage diode D1 in the power switching circuit must be greater than the positive terminal voltage Vcn-1 of the next highest battery.

[0032] In some embodiments, in order to provide a bias current for the low-voltage current mirror, a reference current source Ib is further included, and the reference current source Ib is connected to the drain and the gate of the low-voltage current mirror tube Ma0.

[0033] This embodiment further includes a low-voltage current mirror tube Mb1 , which provides a bias current for the high-voltage current mirror tube Me0 through the high-voltage isolation tube Mc0 .

[0034] The current of the pull-down current source of the disconnection detection circuit proposed in this paper is calculated as follows. Assuming that the battery voltage detection port of the disconnection detection circuit is connected to a 0.1μF filter capacitor, the voltage difference between the two ends of the disconnected battery is 4.25V, and the threshold voltage of the NMOS switch tube is 0.7V. If the disconnection of the battery is to be detected, the port voltage needs to be reduced by 4.95V. Assuming that the overcharge protection delay of the chip is 1s, in order to detect whether the battery is disconnected within the overcharge detection delay time, the required current Therefore, the pull-down current required in this solution is relatively small, and a current mirror with too large size is not required, thus saving chip area overhead.

[0035] In summary, the battery disconnection detection circuit of the present invention uses a switch tube to realize the function of the comparator, and does not need to use a large number of comparators and comparator reference voltage generation circuits, which effectively saves chip area. The switch tube in the present invention can be realized by an NMOS or PMOS switch tube. At the same time, the disconnection detection circuit can be conveniently expanded from 2-cell to multi-cell lithium battery disconnection detection applications. The battery disconnection detection circuit of the present invention can protect the battery in a timely and effective manner during the battery disconnection, and has good reliability. When the battery is disconnected, the chip pin voltage corresponding to the battery will be slowly pulled down by the pull-down current source. When the chip pin voltage is lower than the over-discharge detection voltage, it will first enter the over-discharge protection state, turn off the discharge MOS tube, and when the chip pin voltage is pulled down to a sufficiently low voltage, the disconnection detection signal is flipped, and the disconnection protection state is entered. The present invention requires that the disconnection detection circuit can detect whether the battery is disconnected within the overcharge detection delay time. Therefore, during the disconnection detection period, even if a battery in the battery pack is over-discharged or overcharged, the chip can protect the battery pack within the effective time, ensuring the safety of the battery pack.

[0036] It should be noted that, although the above embodiments have been described in this article, the patent protection scope of the present invention is not limited thereby. Therefore, based on the innovative concept of the present invention, changes and modifications made to the embodiments described herein, or equivalent structures or equivalent process changes made using the contents of the present invention specification and drawings, directly or indirectly applying the above technical solutions to other related technical fields, are all included in the patent protection scope of the present invention.

Claims

1. A disconnection detection circuit, characterized in that: It includes a power switching circuit, a reference voltage source VCC, and B2-Bn disconnection detection subunits; The input end of the power switching circuit is connected to the battery protection chip pin Vcn and the battery protection chip pin Vcn-1, and the output end of the power switching circuit is connected to the power supply VDD. The power switching circuit is used to provide the power supply VDD from the second highest battery BATn-1 when an open circuit occurs between the battery protection chip pin Vcn and the highest battery BATn; the B2~Bn disconnection detection subunit includes high-voltage current mirror tubes Mh2~Mhn, low-voltage current mirror tubes Ma2~Man, low-voltage current mirror tubes Mb2~Mbn, high-voltage isolation tubes Mc2~Mcn and switch tubes Mf2~Mfn, Mg2~Mgn, the source of the high-voltage current mirror tube Mhi is connected to the power supply VDD, and the drain of the high-voltage current mirror tube Mhi is connected to the switch tube M The gate of gi is connected to the drain of the switch tube Mfi, the gate of the switch tube Mfi is connected to the battery protection chip pin Vci-1, the source of the switch tube Mfi is connected to the battery protection chip pin Vci and the drain of the high-voltage isolation tube Mci, the gate of the high-voltage isolation tube Mci is connected to the reference voltage source VCC, the source of the high-voltage isolation tube Mci is connected to the drain of the low-voltage current mirror Mai, the source of the switch tube Mgi is connected to the reference voltage source VCC, the drain of the switch tube Mgi is connected to the drain of the low-voltage current mirror tube Mbi and an input end of the OR gate A1, the source of the low-voltage current mirror tube Mai and the source of the low-voltage current mirror tube Mbi are grounded, wherein 2≤i≤n, and the output signal of the OR gate A1 is the disconnection detection signal VBLD; The B1 line break detection subunit includes a high-voltage current mirror tube Me1, a high-voltage current mirror tube Me2, a low-voltage current mirror tube Ma1, a high-voltage isolation tube Mc1, and switch tubes Md1, Md2, and Md3. The source electrodes of the high-voltage current mirror tube Me1 and the high-voltage current mirror tube Me2 are connected to the power supply VDD, the drain electrode of the high-voltage current mirror tube Me1 is connected to the source electrode of the switch tube Md2, the gate electrode of the switch tube Md2 and the gate electrode of the switch tube Md1 are connected to the output signal dn of the line break detection control circuit of the lowest battery BAT1, and the switch tube Md2 is connected to the output signal dn of the line break detection control circuit of the lowest battery BAT1. The drain of the switch tube Md1 is connected to the drain of the switch tube Md1, the gate of the switch tube Md3 and the battery protection chip pin Vc1, the source of the switch tube Md1 is connected to the drain of the high-voltage isolation tube Mc1, the gate of the high-voltage isolation tube Mc1 is connected to the reference voltage source VCC, the source of the high-voltage isolation tube Mc1 is connected to the drain of the low-voltage current mirror tube Ma1, the source of the low-voltage current mirror tube Ma1 and the source of the switch tube Md3 are grounded, and the drain of the switch tube Md3 is connected to the drain of the high-voltage current mirror tube Me2 and the input end out1 of the lowest battery BAT1 disconnection detection control circuit; It also includes a lowest battery cell BAT1 disconnection detection control circuit, the lowest battery cell BAT1 disconnection detection control circuit includes a D flip-flop A6, the D end of the D flip-flop A6 is grounded, the clk end of the D flip-flop A6 is connected to the output end of the delay circuit C2, the input end of the delay circuit C2 is connected to the input end out1 through the level conversion circuit C1, and the output end Q of the D flip-flop A6 is connected to the output signal dn through the level conversion circuit C3; It also includes a reference current source Ib, which is connected to the drain and gate of the low-voltage current mirror tube Ma0, the gates of the low-voltage current mirror tubes Ma1 to Man, and the gates of the low-voltage current mirror tubes Mb1 to Mbn, and the source of the low-voltage current mirror tube Ma0 is grounded; It also includes a low-voltage current mirror tube Mb1, the drain of the low-voltage current mirror tube Mb1 is connected to the source of the high-voltage isolation tube Mc0, the drain of the high-voltage isolation tube Mc0 is connected to the drain and gate of the high-voltage current mirror tube Me0, the gate of the high-voltage current mirror tube Me1, the gate of the high-voltage current mirror tube Me2 and the gates of the high-voltage current mirror tubes Mh2~Mhn, the source of the high-voltage current mirror tube Me0 and the gate of the high-voltage isolation tube Mc0 are connected to the reference voltage source VCC, and the source of the low-voltage current mirror tube Mb1 is grounded.

2. A line break detection circuit according to claim 1, characterized in that: The lowest battery BAT1 disconnection detection control circuit includes a NOR gate A4, a NOR gate A5, a D flip-flop A3 and an inverter A2, wherein an input end of the inverter A2 is connected to an out2 end, and the out2 end is connected to a drain of the switch tube Mg2, an output end of the inverter A2 is connected to a clk end of the D flip-flop A3, an inverting output end Q of the D flip-flop A3 is connected to an input end of the NOR gate A5, an output end of the NOR gate A5 is connected to a set end of the D flip-flop A6, another input end of the NOR gate A5 is connected to an output end of the NOR gate A4, an input end of the NOR gate A4 is connected to an output signal up of an inverting output end Q of the D flip-flop A6, and another input end of the NOR gate A4 is connected to an input end out1.

3. A disconnection detection circuit according to claim 1, characterized in that: The power switching circuit includes a resistor R1, a diode D1 and a switch tube Mp1, the gate of the switch tube Mp1 is connected to one end of the resistor R1, the anode of the diode D1 and the battery protection chip pin Vcn, the source of the switch tube Mp1 is connected to the power supply voltage VDD and the cathode of the diode D1, the drain of the switch tube Mp1 is connected to the battery protection chip pin Vcn-1, and the other end of the resistor R1 is grounded.

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