Charging and discharging management chip for converting lithium battery into dry battery

Abstract

The invention aims to provide the chip for charging and discharging management of the lithium battery to the dry battery, the chip has two working modes of charging and discharging, and the working mode of the chip can be judged by comparing the voltage VOUT of the OUT pin with the voltage VBAT of the BAT pin. When VOUTgt is detected; and when VBAT + 100mV, the charging management module is in a charging management mode. When the number is VOUT < lt >; and in VBAT, the device is in a discharge management mode (Buck DC / DC mode or LDO mode). And in the discharge mode, the device has the functions of under-voltage protection, short-circuit protection, over-current protection and over-temperature protection. And the charging mode has an over-temperature protection function. Product conditions can be observed in charging and discharging processes according to states of the indicating lamps, and the indicating lamps can indicate charging, full charging, short circuit and under-voltage states. The chip is provided with an NTC pin which can monitor the battery temperature in real time and ensure the safety of the battery.

Description

Technical Field

[0001] The present invention is a special chip for charging and discharging management of lithium battery to dry cell. Background Art

[0002] When charging, it can charge 3.7V lithium batteries, and the charging current can be set to a maximum of 1A; when discharging, it is converted to 1.5V output through a synchronous buck converter to simulate a dry battery, and the output voltage is linearly related to the lithium battery voltage. Summary of the invention

[0003] The purpose of the present invention is to provide a dedicated chip for lithium battery to dry battery charge and discharge management, in which the output dry battery voltage changes with the lithium battery voltage.

[0004] The technical solution adopted by the present invention is as follows:

[0005] When discharging, a 1MHz synchronous buck converter is used for discharge, and the discharge current can reach 3A. There are two output modes: Mode 1: When the BAT voltage is above 3.5V, it is kept constant at 1.5V. When the BAT voltage is lower than 3.5V, the output dry battery voltage is linearly related to the lithium battery voltage; Mode 2: The BAT voltage starts from the full charge voltage, and the output dry battery voltage is linearly related to the lithium battery voltage.

[0006] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 The internal structure diagram of the chip circuit of the present invention is

[0008] Figure 2 The chip application circuit diagram of the present invention is

[0009] Figure 3 The chip pin arrangement diagram of the present invention is

[0010] Figure 4 This is a chip pin diagram of the present invention

[0011] Figure 5 This is the electrical characteristic parameter diagram of the chip of the present invention

[0012] Figure 6 This is the relationship diagram between the dry cell voltage and the lithium battery voltage output by the chip of the present invention DETAILED DESCRIPTION

[0013] To make the objectives, technical solutions and advantages of the present invention more clear, the following will describe the technical solutions in the present invention clearly and completely in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0014] As shown in the figure, the present invention is a lithium battery to dry battery charge and discharge management chip, and the chip has two working modes: charging and discharging. The working mode is judged by comparing the voltage VOUT of the OUT pin and the voltage VBAT of the BAT pin.

[0015] Judgment of working mode:

[0016] When VOUT > VBAT + 100 mV, SM5102 works in the charge management mode (Charge mode), and its function is to use the voltage at the OUT terminal as the working power supply to linearly charge the single lithium battery at the BAT terminal.

[0017] When VOUT < VBAT, SM5102 works in the discharge management mode (Buck DC / DC mode or LDO mode), and its function is to convert the voltage of the single lithium battery at the BAT terminal into the output voltage of 1.5 V of a single dry battery and output it from the OUT terminal. When overloaded, the discharge mode is the Buck DC / DC mode, which can achieve the output ability of a high load current. When lightly loaded, the discharge mode is the LDO mode, which can achieve high efficiency at no load.

[0018] V42: The output dry battery voltage has a linear relationship with the lithium battery voltage. When the lithium battery voltage is 4.2 V, the dry battery output voltage is 1.55 V. As the lithium battery voltage gradually decreases during the discharge process, the dry battery output voltage also decreases accordingly, simulating the characteristics of a dry battery. The specific relationship is as follows in the table.

[0019] VBAT VOUT 4.2V 1.55V 4.0V 1.49V 3.8V 1.42V 3.6V 1.35V 3.4V 1.28V 3.2V 1.22V 3.0V 1.15V 2.8V 1.10V

[0020] V35: When the BAT voltage is above 3.5 V, the output dry battery voltage remains constant at 1.5 V. When the BAT voltage is below 3.5 V, the output dry battery voltage has a linear relationship with the lithium battery voltage. The specific relationship is as follows in the table.

[0021] VBAT VOUT 4.2V 1.5V 4.0V 1.5V 3.8V 1.5V 3.6V 1.5V 3.4V 1.45V 3.2V 1.34V 3.0V 1.29V 2.8V 1.18V

[0022] Discharge working mode:

[0023] After judging that the system enters the discharge management mode, SM5102 first enters the BUCK DC / DC mode. When the load current is lower than 3mA, the detection system enters the LDO mode after 1s. If it enters the LDO mode, when the load current is higher than 25mA, the detection system enters the BUCK DC / DC mode. The discharge working mode also includes over-current protection, short-circuit protection, over-temperature protection and synchronous rectifier.

[0024] BUCK DC / DC mode:

[0025] The chip achieves the purpose of voltage reduction by switching on / off the internal P-MOS main switch tube and N-MOS synchronous rectifier tube and external inductor and output capacitor.

[0026] Under normal conditions, the chip works in PWM mode, in which the operating frequency remains constant. Since there is a current-type feedback compensation circuit inside the chip, the chip does not require external compensation components; the chip also uses a feedforward circuit to improve the voltage transient response performance of the circuit. At the falling edge of the sawtooth wave generated by the internal waveform generator, the P-MOS tube is turned on; when the PWM comparator flips or the overvoltage protection condition occurs or the current limit condition occurs, the P-MOS tube will be turned off and the N-MOS tube will be turned on. When the P-MOS tube is turned on again or the reverse current is detected, the N-MOS tube will be turned off. If the reverse current is detected and the maximum inductor current is less than 500mA, the chip will enter the PFM mode, thereby reducing the operating current at light load.

[0027] Overcurrent protection:

[0028] When the chip works in DC / DC mode, its internal over-current protection circuit always monitors the current passing through the P-MOS tube. When this current is greater than the current limit value (ILIM), the P-MOS tube will be turned off to prevent the inductor current from further increasing; in the next pulse, if the P-MOS tube current is already less than the current limit value (ILIM), the chip will return to normal operation from the over-current protection state. However, once an over-current condition occurs again, the P-MOS tube will be immediately turned off and re-enter the over-current protection state.

[0029] Short circuit protection:

[0030] When the OUT terminal is short-circuited to ground, the chip will enter the hiccup mode and start once every 100ms to detect whether the short-circuit fault is removed, thereby greatly reducing the input current of the battery terminal and effectively reducing the heating of the circuit. After the short-circuit fault is removed, the circuit will immediately enter the normal DC / DC working mode.

[0031] Overheat protection:

[0032] When the internal temperature of the chip circuit exceeds the overtemperature protection threshold (TOTP), the circuit will turn off the P-MOS and N-MOS tubes and prohibit the output voltage; when the chip operating temperature drops to the overtemperature protection recovery threshold (TOTP-TOTP-HYS), the circuit will return to normal working state and the P-MOS will automatically turn on in the next cycle.

[0033] Synchronous rectifier:

[0034] An N-MOS synchronous rectifier is provided inside the chip, so that no additional Schottky rectifier diode is required externally. At the same time, the conduction voltage drop of the N-MOS tube is lower than that of the usual Schottky rectifier diode, thereby improving the efficiency of the circuit.

[0035] LDO working mode:

[0036] When the load current is lower than 3mA, the system enters LDO mode. The chip realizes the output of 1.5V dry battery by switching on / off with an internal P-MOS tube and external output capacitor. There is a compensation circuit inside, so that the chip does not need external compensation components. The power consumption of the chip is only 6uA when unloaded to achieve high efficiency. An N-MOS synchronous rectifier is provided inside the chip, so that no additional Schottky rectifier diode is required externally. At the same time, the conduction voltage drop of the N-MOS tube is lower than that of the usual Schottky rectifier diode, thereby improving the efficiency of the circuit.

[0037] Charging working mode:

[0038] When the OUT voltage (VOUT) is greater than the battery voltage by 100mV (VOUT>VBAT+100mV), the chip starts a charging cycle.

[0039] If the BAT terminal voltage is less than the trickle charge threshold voltage (VTRIKL), the battery will enter the trickle charge state, in which the battery charging current is 1 / 10 of the set charging current (ICHG), and the battery is safely pre-processed. If the trickle charge can raise the battery voltage above VTRIKL, the battery will enter the pre-charge state, in which the battery charging current is 1 / 10 of the set charging current, so that the battery voltage is raised to a safe level for full current charging. When the trickle charge is completed, the charger will enter the constant current charging mode and provide the battery with the set charging current. When the BAT terminal voltage approaches the charging voltage value (VVC), the chip enters the constant voltage charging mode and the charging current begins to decrease. When the charging current drops to 1 / 10 of the set charging current, the circuit gives a charging end signal at the VLED terminal, indicating that the battery is fully charged. At this point, it can be considered that a charging cycle is over.

[0040] Set the charging current:

[0041] The charging current is set using a resistor connected between the ISET pin and ground. The battery charging current is 1000 times the output current of the ISET pin (typical value, internally modifiable). The charging current output from the BAT pin can be determined at any time by monitoring the ISET pin voltage, as follows:

[0042]

[0043] Charging end:

[0044] When the BAT terminal voltage reaches the constant voltage float charge voltage (VCV) and the charging current drops to 1 / 10 of the set charging current, it can be considered that a charging cycle is completed.

[0045] Overheat protection:

[0046] In charging mode, when the internal temperature of the chip circuit exceeds the overheat protection threshold (OTP1), the circuit will slowly reduce the charging current and reduce the power consumption of the circuit to protect the circuit from damage; when the chip operating temperature drops to the overheat protection threshold (OTP1), the circuit will return to the normal charging current.

[0047] NTC:

[0048] The chip integrates NTC function and can detect battery temperature. When the chip is working, NTC PIN outputs 20uA current and detects the voltage of NTC PIN to judge the current battery temperature.

[0049] In the charging state: when the NTC PIN detects a voltage of 1.32V, it means the battery is at a low temperature of 0 degrees, and the battery charging is stopped; when the NTC PIN detects a voltage of 0.56V, it means the battery is at a medium temperature of 45 degrees, and the battery charging is stopped;

[0050] In the discharge state: when the NTC PIN detects a voltage of 1.52V, it means the battery is at a low temperature of -15 degrees, and the discharge is stopped; when the NTC PIN detects a voltage of 0.38V, it means the battery is at a high temperature of 60 degrees, and the discharge is stopped;

[0051] LED light status:

[0052] The chip provides an open-drain structure output LED terminal, which is connected to a high level externally through an indicator light (LED), and the LED lamp has a constant current of 3mA. The circuit controls the output of the LED terminal (high impedance, low level, square wave) according to different charging states, and indicates the corresponding charging state through an external LED, as shown in the following table.

[0053]

Claims

1. A lithium battery to dry battery charge and discharge management chip, characterized in that: When the BAT voltage is above 3.5V, the output dry battery voltage is kept constant at 1.5V. When the BAT voltage is lower than 3.5V, the output dry battery voltage is linearly related to the lithium battery voltage.

2. The lithium battery to dry cell charge and discharge management chip according to claim 1, characterized in that: The charging current in the charging mode is set by a resistor connected between the ISET pin and ground. The battery charging current is 1000 times the output current of the ISET pin. The charging current output from the BAT pin can be determined at any time by monitoring the ISET pin voltage, as shown below:

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