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BQ76920: - Cell 1 become ~0V and, cell 2: ~5.1V and other cells are nornal.

Part Number: BQ76920

Hi, I am using BQ76920 for 20S BMS. This chip will handle 5 upper cells. Here is the schematic of it:

I measured the voltage on C56 and C29 already (~1.6V) even the input voltage (A15, A16) are 3.44V (li-ion 18650 battery). I've booted the device by connect the pin TS1 to 3.44V via 10k resistor manually.

Is the chip damaged?

Thanks for your help!

  • Hi Dam,
    It sounds like the chip is damaged. You can measure the voltage across R32, R33, and R34 to confirm current is going into the node. Then you have to be sure it is going into the IC rather than the capacitors. Capacitors can short or leak, but if both C56 and C29 are 1.6V it sounds like VC1 and VC0 are shorted together. Of course check for a solder bridge or contamination between the pins.

    Since you mention it is a 20S implementation, check to see if it may be a random connection issue.  If the battery- mates first, the capacitors on the lower devices may be holding GNDD at a low voltage, when A15 and/or A16 mate this may put a high voltage on VC0 and VC1, these pins have the lowest abs max limits of the inputs.