Introduction to the working principle of lithium battery protection board
Lithium battery protection board usually includes control IC, MOS switch and auxiliary device NTC, ID memory and so on. Among them, the control IC controls the MOS switch to be turned on under all normal conditions, so that the cell can communicate with the external circuit, and when the cell voltage or loop current exceeds the specified value, it immediately controls the MOS switch to turn off to protect the safety of the cell .
NTC: Negative temperature coefficient resistance (the higher the temperature, the smaller the resistance), which protects the mobile phone.
ID: Play the role of decoding (identification resistance) Resistance: Play the role of current limiting and sampling
Capacitor: it acts as an instant voltage stabilizing and filtering function
Fuse: blown or fuse, melted when short-circuited, irrecoverable
Ptc: The positive temperature coefficient device is usually referred to as PTC in the profession. PTC in battery products can prevent the occurrence of high-temperature discharge and unsafe large current of the battery. According to the battery voltage, current density characteristics and application environment, there are special requirements for PTC. It is a very important component in battery assembly products, and it bears an important mission for battery safety. Its performance and quality are also an important factor of battery pack performance and quality. When an overcurrent occurs in the circuit, the heat generated by the large current flowing through the polymer resettable fuse is sufficient to melt the polymer resin matrix and expand its volume, thus cutting off the chain-like conductive path formed by the conductive particles, resulting in the polymer resetting fuse After troubleshooting, the resin cools and crystallizes again, the volume shrinks, the conductive particles form a conductive path again, and the device returns to low impedance. Therefore, some people call it a recoverable fuse or Resettable fuse.
1. The function of lithium battery protection board:
Overcharge protection: When the cell voltage rises to a certain value (below 4.4V), the protection board will cut off the charging circuit.
Over-discharge protection: When the cell voltage drops to a certain value (above 2.2V), the protection board will cut off the discharge circuit.
Short circuit protection: When the positive and negative terminals of the battery are short-circuited, the circuit can be quickly cut off to protect the cells.
Overcurrent protection: When the battery output current exceeds a certain value (about 2A), the protection circuit will cut off the output circuit.
Other auxiliary functions: There are usually NTC, identification resistor and decoding chip on the protection board, the main function is to ensure that the battery can be charged and used normally with the host and the original charger.
2. The coordination function of the lithium battery protection board includes the following points:
(1) Overcharge detection voltage: In the normal state, Vdd gradually rises to the voltage between VDD and VSS when the CO terminal changes from high level to low level.
(2) Overcharge release voltage: In the charging state, Vdd gradually decreases to the voltage between VDD and VSS when the CO terminal changes from low level to high level.
(3) Overdischarge detection voltage: Under normal conditions, Vdd gradually decreases to the voltage between VDD and VSS when the DO terminal changes from high level to low level.
(4) Overdischarge release voltage: In the overdischarge state, Vdd gradually rises to the voltage between VDD and VSS when the DO terminal changes from low level to high level.
(5) Overcurrent 1 detection voltage: Under normal conditions, VM gradually rises to the voltage between VM and VSS when DO changes from high level to low level.
(6) Overcurrent 2 detection voltage: In the normal state, VM rises from OV at a speed of 1ms or more and 4ms or less to the voltage between VM and VSS when the DO terminal changes from high to low.
(7) Load short-circuit detection voltage: Under normal conditions, VM starts from OV and rises to the voltage between VM and VSS when the DO terminal changes from a high level to a low level at a speed of 1μS or more and 50μS or less.
(8) Charger detection voltage: In the over-discharge state, VM gradually decreases with OV to the voltage between VM and VSS when DO changes from low level to high level.
(9) Current consumption during normal operation: Under normal conditions, the current flowing through the VDD pin (IDD) is the current consumption during normal operation.
(10) Overdischarge current consumption: In the discharge state, the current (IDD) flowing through the VDD pin is the overcurrent discharge current consumption.