Typical defect analysis of lithium battery protection plate

July 26, 2020


Typical defect analysis of lithium battery protection plate

No flash, low output voltage, can not take the load

This kind of bad first rule out bad cell (cell originally no voltage or low voltage) if the lousy cell should be tested to see whether the protection plate power consumption is too large, leading to small voltage core.

If the battery cell voltage is average, it is because the whole circuit of the protection board is not connected (virtual welding of components, false welding, poor FUSE, PCB internal circuit is not connected, through-hole is not connected, MOS, IC damage, etc.).

A concrete analysis


The process is as follows:


(I) The black marker pen of the multimeter is connected to the negative pole of the cell. The red marker pen is connected to FUSE and R1 resistors in turn. The Vdd, Dout, and Cout end and P+ ends of the IC (assuming that the cell voltage is 3.8V) are analyzed segment by segment. These test points should all be 3.8V.
If not, there is a problem with the circuit.


1. The voltage at both ends of FUSE is changed: check whether FUSE is on if the circuit in PCB is blocked in the public guide;

If there is a problem with FUSE (poor incoming material, overcurrent damage (MOS or IC control failure), or physical problem (FUSE is burned before MOS or IC action), then FUSE with a wire and continue to analyze in the future.


2. The voltage at both ends of R1 resistance is changed: check the Resistance value of R1; if the resistance value is abnormal, it may be virtual welding. The opposition may crack itself.

If the resistance is not out of kilter, it may be the resistance inside the IC that is in trouble.


3. IC test terminal voltage has been changed: the Vdd terminal is connected with the R1 resistor.

If the END of Dout or Cout is out of order, it is because of IC virtual welding or damage.


4. If the first voltage is unchanged, check the abnormal voltage between B- and P+ because the front pole of the protection plate is blocked through the hole.


(II) The red watch pen of the multimeter is connected to the positive pole of the battery cell. After activating the MOS tube, the black watch pen is connected to the MOS tube with pins 2, 3, 6, and 7 in turn, spend.


MOS tube 2, 3 pins, 6, 7 pin voltage changes, indicating that the MOS tube abnormal.


2. If the MOS tube voltage is unchanged and the P-terminal energy is out of order, it is because the protection plate is blocked through the hole.


2. A short circuit is unprotected

1. Problems with the resistance at the VM end: an IC2 pin can be connected with a multimeter and a MOS pipe pin connected with the opposition at the VM end.
See whether the resistance and IC, MOS pin virtual welding.


2. IC and MOS malfunction: the over-discharge protection, overcurrent protection, and short-circuit protection share the same MOS tube. If the MOS problem causes the short-circuit malfunction, the board shall have no over-discharge protection function.


3. The above are the defects under normal conditions. The short-circuit disorder caused by poor IC and MOS equipment may also occur.

For example, if the BK-901 appears in the early stage, the IC internal delay time of the model "312D" is too long, causing MOS or other components to be damaged before the IC makes the corresponding action control.

Note: The easiest and most direct way to admit whether IC or MOS is out of order is to replace the component in question.


3. No self-recovery for short circuit protection

1. IC used in planning initially has no self-recovery function, such as G2J, G2Z, etc.


2. Instrument setting short circuit recovery time is too short, or the load is not removed during the quick circuit test. For example, the meter fails to remove the meter pen from the test end after short-circuiting using the multimeter voltage file (the multimeter is equivalent to a load of several megabytes).


3. Electric leakage between P+ and P-. For example, there is rosin with impurities between the pads, yellow gum with impurities or capacitance between P+ and P- is broken down, and ICVdd is broken down between Vss.

(Resistance ranges from a few K to a few hundred K).


4. Assuming that the above is no problem, maybe IC is broken, the resistance value between each pin of IC can be checked.


4. Large internal resistance

1. Since MOS internal resistance is relatively stable and abundant, FUSE or PTC are relatively simple components with modified internal resistance that should be the first suspect.


2. Assuming that FUSE or PTC resistance is reasonable, the pass-through resistance value between P+ and P-pad and the component surface is detected according to the protection plate's structure. Micro-breakage may occur in the pass-through, and the resistance value is relatively large.


3. Assuming that there is no problem with the above mentioned, it is necessary to doubt whether THE MOS is abnormal.

Secondly, the thickness of the kanban (whether it is bent), because bending may cause abnormal pin welding;

Put the MOS tube under the microscope to observe whether it is broken or not.

After all, the MOS pin resistance is checked with a multimeter to see if it has been broken down.


Five, ID abnormal

1, ID resistance itself due to virtual welding, cracking, or due to the resistance material not pass the abnormity: can weld both ends of the opposition from scratch, if ID healthy after rewelding is virtual resistance welding if cracking resistance will crack in the middle after rewelding.


2, ID through the hole without conduction: multimeter can be used to check both ends of the tunnel.


3. Internal circuit problems: the welding resistance paint can be scraped to see whether the internal circuit is disconnected or short circuit phenomenon.