Common bad analysis of battery protection board
1. No display, low output voltage, no load:
For such defects, first eliminate the bad battery (the battery has no voltage or the voltage is low). If the battery is bad, the self-consumption of the battery management system should be tested to see if the self-consumption of the protection board is too large and the battery voltage is low. If the cell voltage is normal, it is because the entire circuit of the protection board is blocked (components are soldered, false soldered, FUSE is poor, the internal circuit of the battery protection board is blocked, the via is blocked, MOS, IC is damaged, etc.). The specific analysis steps are as follows:
(1) Connect the black test lead of a multimeter to the negative pole of the battery cell, and connect the red test lead to the FUSE, R1 resistor terminals, the Vdd, Dout, and Cout terminals of the IC, and the P+ terminal (assuming the battery cell voltage is 3.8V), and analyze it section by section. These test points should all be 3.8V. If not, there is a problem with this section of the circuit.
1. There is a change in the voltage across the FUSE: test whether the FUSE is turned on, if it is turned on, the internal circuit of the PCB board is not turned on; if it is not turned on, there is a problem with the FUSE (poor incoming material, overcurrent damage (MOS or IC control failure), There is a problem with the material (the FUSE is burned out before the MOS or IC is activated), then use a wire to short the FUSE, and continue to analyze later.
2. There is a change in the voltage across the R1 resistor: test the resistance value of R1. If the resistance value is abnormal, it may be a virtual weld and the resistor itself is broken. If the resistance value is not abnormal, there may be a problem with the internal resistance of the IC.
3. There is a change in the voltage of the IC test terminal: the Vdd terminal is connected to the R1 resistor. Dout, Cout end abnormal, it is due to the IC weak welding or damage.
4. If there is no change in the previous voltage and the voltage between test B- and P+ is abnormal, it is because the positive via of the protection plate is blocked.
(2) Connect the red test lead of the multimeter to the positive electrode of the battery. After activating the MOS tube, the black test lead is connected to the MOS tube 2, 3, 6, 7 and P- terminal in turn.
1. There is a change in the voltage of MOS tube 2, 3, 6 and 7 pins, which indicates that the MOS tube is abnormal.
2. If there is no change in the voltage of the MOS tube and the voltage at the P- terminal is abnormal, it is because the negative through hole of the protection plate is blocked.
2. No short circuit protection:
1. There is a problem with the resistance of the VM terminal: use a multimeter to connect one test pen to the IC2 pin, and one test pen to the MOS pin connected to the VM terminal resistor to confirm the resistance value. Check whether the resistance and IC, MOS pins are soldered.
2. IC and MOS abnormality: Since the over-discharge protection and over-current and short-circuit protection share the same MOS tube, if the short-circuit abnormality is due to a MOS problem, the board should have no over-discharge protection function.
3. The above are defects under normal conditions, and short-circuit abnormalities caused by poor IC and MOS configurations may also occur. For example, in the BK-901 that appeared in the previous period, the delay time in the IC with the model of ‘312D’ was too long, which caused the MOS or other components to be damaged before the IC took the corresponding action control. Note: The easiest and direct way to determine whether an IC or MOS is abnormal is to replace the suspected components.
3. Short-circuit protection without self-recovery:
1. The IC used in the design has no self-recovery function, such as G2J, G2Z, etc.
2. The short-circuit recovery time of the instrument is too short, or the load is not removed during the short-circuit test. For example, the test leads are not removed from the test end after the short-circuit test leads are short-circuited with the multimeter voltage file (the multimeter is equivalent to a load of several megabytes).
3. Leakage between P+ and P-, such as impurity rosin between the pads, impurity yellow glue or P+, P- capacitance breakdown, IC Vdd to Vss breakdown. (The resistance value is only a few K to several hundred K).
4. If none of the above is a problem, the IC may be broken down, and the resistance between the pins of the IC can be tested.
4. Large internal resistance:
1. Since the internal resistance of MOS is relatively stable and large internal resistance appears, the first thing to suspect should be the components that are relatively easy to change such as FUSE or PTC.
2. If the resistance of FUSE or PTC is normal, check the resistance of the via hole between the P+ and P- pads and the component surface depending on the structure of the protection board. The via may have micro-breaks and the resistance is relatively large.
3. If there are no problems with the above, it is necessary to suspect whether the MOS is abnormal: first determine whether there is a problem with the welding; secondly, the thickness of the billboard (whether it is easy to bend), because the bending may cause abnormal soldering of the pins; then the MOS tube Put it under a microscope to observe whether it is broken; finally, use a multimeter to test the resistance of the MOS pin to see if it is broken down.
Fifth, the ID is abnormal:
1. The ID resistance itself is abnormal due to virtual welding, breakage or failure of the resistance material: both ends of the resistance can be re-welded. If the ID is normal after re-welding, the resistance is virtual welding. If it is broken, the resistance will be split after re-welding. open.
2. The ID via is not conductive: use a multimeter to test both ends of the via.
3. There is a problem with the internal circuit: you can scrape the solder mask to see if the internal circuit is disconnected or short-circuited.