Shunrui Core Introduces You to Single-CellLi-ion Battery Protection ICProposal:
A low-power single-cell lithium-ion battery protection circuit has been designed. This circuit not only provides overcharge, over-discharge, and over-discharge current protection for lithium-ion batteries but also includes functions such as abnormal charging protection and prevention of charging at 0V. It is fabricated using a 1.0μm double-well CMOS process.
Function and Principle Analysis of Lithium Battery Protection IC
Normal Status: Both the charging control FET2 and the discharging control FET1 are flipped open when the battery voltage is above the over-discharge detection voltage and below the overcharge detection voltage, and the VM terminal voltage is above the charger detection voltage and below the overcurrent detection voltage.
This is when the spontaneous charging and discharging can be halted. This state is known as the normal state.
Overcharge Protection: During the charging process, when the battery voltage exceeds the overcharge detection voltage, and this condition persists beyond the overcharge detection delay time, the control circuit outputs a low level, shutting off the charging control FET2, and stopping the charging.
Overcurrent Protection: Overcurrent protection encompasses overcurrent protection, secondary overcurrent protection, and short-circuit protection. When the discharge current exceeds a certain level, the VM terminal voltage rises, surpassing the overcurrent detection voltage. If this condition persists beyond the overcurrent detection delay time, the control circuit outputs a low level, shutting off the discharge control FET1, and halting the discharge. During the discharge process, the VM terminal voltage is the voltage drop across the two FETs in the conductive state, i.e., VVM = I × 2RFET. Here, I is the current passing through the FET, i.e., the discharge current, and RFET is the FET's on-state resistance.
Overcharge Protection: If the current during charging exceeds a certain level, causing the VM terminal voltage to drop, and this condition persists beyond the overcharge detection delay time, the control circuit will shut off the charging control using FET2, halting charging. Once the VM terminal voltage recovers and rises above the set value, the charging control FET1 is activated, and the overcharge protection is lifted.
Battery Charging Halt at Zero Volts: When a battery is left unused for a long period, it will self-discharge, causing the battery voltage to drop to zero volts. Some lithium batteries are not suitable for recharging after being fully discharged due to their inherent characteristics. When the battery voltage falls below a certain set value, the gate of the charging control FET2 is held at a low potential, halting charging. Charging is only permitted when the battery's self-voltage is above the zero-volt charging halt voltage.
The lithium battery protection circuit is mainly composed of a reference source, a comparator, a logic control circuit, and some additional functional blocks. The comparator detects the reference voltage required for its operation, which is provided by a reference source circuit. This reference source must maintain high precision and low power consumption during normal operation to meet the chip's requirements and operate normally when the power supply voltage drops to as low as 2.2V.
