Tool/software:
Hello: When stacking two BQ76940 IC's we seem to be in a situation that whenever we turn on into a capacitive load, or crowbar is put on the output we fail the upper BQ76940 IC.
We are thinking this is due to a hard ring on the BMS IC cell inputs. We have attempted to mitigate this with extra diodes, larger filter capacitors and larger filter resistors. The behavior is much more pronounced when using high ESR cells (think cheap 18650's for testing, around .2 ohms) when we use with our production cells that are around .05 ohms, the ring is less, but a crowbar will still kill the upper IC.
We can only reproduce this when connecting to a capacitive load, or crowbar. We see a ring in the 2-4 us range on the cell inputs that can go negative a few volts or over range. We suspect the voltage is what is killing the IC's, we don't see any other path for current. It's mostly a system issue we think, and the lower the ESR of the cell the more robust the BMS IC is in this situation. The ring seems to be most pronounced on the upper BMS IC as well. Any comments or feedback would be greatly appreciated.