common bad analysis of lithium battery protection board

May 22, 2019

Common bad analysis of protection board

First, no display, low output voltage, can not afford the load:

Such defects first eliminate the bad cell (the battery has no voltage or low voltage), if the battery is bad, the self-consumption of the protection board should be tested to see if the protection board consumes too much power and the voltage of the battery is low. If the cell voltage is normal, it is because the entire circuit of the protection board is unreachable (component soldering, false soldering, poor FUSE, internal circuit of the PCB board, via hole, MOS, IC damage, etc.). The specific analysis steps are as follows:

(1) Use the black meter of the multimeter to connect the negative pole of the battery. The red test lead is connected to the FUSE and R1 resistors at both ends, the Vdd, Dout, Cout end of the IC, and the P+ end (assuming the voltage of the battery is 3.8V). These test points should all be 3.8V. If not, there is a problem with this segment of the circuit.

1. There is a change in the voltage across FUSE: Test whether FUSE is turned on. If it is turned on, the internal circuit of the PCB board is unreachable. If it is not turned on, there is a problem with FUSE (bad material, overcurrent damage (MOS or IC control failure), There is a problem with the material (FUSE is burned before the MOS or IC action), then short the wire with FUSE and continue to analyze.

2. The voltage across the R1 resistor changes: Test the resistance value of R1. If the resistance value is abnormal, it may be a virtual solder, and the resistor itself is broken. If there is no abnormality in the resistance value, there may be a problem with the internal resistance of the IC.

3. There is a change in the voltage at the IC test terminal: the Vdd terminal is connected to the R1 resistor. Abnormal Dout and Cout are due to IC soldering or damage.

4. If there is no change in the previous voltage, the voltage between the test B- and P+ is abnormal, because the positive hole of the protection plate is not open.

(B), the multimeter red pen connected to the positive pole of the battery, after the activation of the MOS tube, the black test pen is connected to the MOS tube 2, 3 feet, 6, 7 feet, P-end.

1. MOS tube 2, 3 feet, 6 or 7 pin voltage changes, it means the MOS tube is abnormal.

2. If the MOS tube voltage does not change, the P-terminal voltage is abnormal, because the negative hole of the protection board is not open.

Second, short circuit without protection:

1. There is a problem with the VM end resistor: the IC2 pin can be connected with a multimeter and a stylus pen connected to the MOS tube pin connected to the VM end resistor to confirm the resistance value. Look at the resistance and the IC, MOS pins have no solder joints.

2. IC, MOS abnormality: Since the over-discharge protection and the over-current and short-circuit protection share a MOS tube, if the short-circuit abnormality is due to a problem with the MOS, the board should have no over-discharge protection function.

3. The above is a bad condition under normal conditions, and there may be a short circuit abnormality caused by poor IC and MOS configuration. As in the previous BK-901, the delay time of the IC of the model '312D' was too long, causing the MOS or other components to be damaged before the IC made the corresponding action control. Note: The easiest and straightforward way to determine if an IC or MOS has an abnormality is to replace a suspect component.

Third, short circuit protection has no self-recovery:

1. The IC used in the design does not have self-recovery functions, such as G2J, G2Z, etc.

2. The instrument is set to short-circuit recovery time is too short, or the load is not removed when short-circuit test. If the short-circuit test pen is short-circuited with the multimeter voltage file, the test pen is not removed from the test end (the multimeter is equivalent to a load of several megabytes).

3. Leakage between P+ and P-, such as rosin with impurities between the pads, yellow plastic with impurities or P+, P-capacitor breakdown, IC Vdd to Vss is broken down. (The resistance is only a few K to a few hundred K).

4. If there is no problem above, the IC may be broken down and the resistance between the IC pins can be tested.

Fourth, the internal resistance is large:

1. Since the internal resistance of MOS is relatively stable and there is a large internal resistance, the first thing to suspect is that the internal resistance of FUSE or PTC is relatively easy to change.

2. If the resistance of FUSE or PTC is normal, the protection board structure detects the resistance of the via between P+ and P-pad and the component surface, and the via may be slightly broken and the resistance is large.

3. If there is no problem with the above, it is necessary to doubt whether the MOS is abnormal: first determine whether there is any problem with the welding; secondly, the thickness of the kanban (whether it is easy to bend), because the bending may cause the pin to be welded abnormally; then the MOS tube Place it under the microscope to see if it breaks. Finally, use a multimeter to test the resistance of the MOS pin to see if it is broken down.

5. ID exception:

1. The ID resistor itself is abnormal due to the soldering, breaking or the resistance material is not closed: the two ends of the resistor can be re-welded. If the ID is normal after re-welding, the resistance is weak soldering. If it is broken, the resistor will be cracked after re-welding. open.

2. The ID via is not conductive: you can test both ends of the via with a multimeter.

3. There is a problem with the internal circuit: the solder resist can be scraped off to see if the internal circuit is disconnected or short-circuited.