Other Parts Discussed in Thread: BQ40Z50, BQSTUDIO
Hi,
We use the BQ40Z50-R1 with the BQ294702 secondary voltage protection IC in a 3S3P Li-Ion battery pack.The schematic is the same as the recommended one in paragraph 9.2 of the BQ40Z50 datasheet except we don't have any LEDs or push buttons.
Our customer has returned a battery which seems dead. Actually the voltage at the pack output is 0V and the battery do not charge when connected to a charger.
Connection to the battery with BqStudio shows that the FUSE bit of the Operation Status A register is set. The fuse pin is driven high (around 6.3V) and the "chemical" fuse is blown.
We concluded that the BQ40Z50 has detected a permanent fail and blown the fuse but when we check the data flash memory, all the black box and PF status data remain to their intitial value of zero and thus we are unable to determine which failure has caused the fuse to blow. We also see one COV safety event and one ASCD safety event in the lifetime but no overvoltage or overcurrent event in the black box or PF status.
You will find attached a screen capture of the BQ40Z50 registers and a data flash export.
We don't understand why the chemical fuse has blown without having any permanent fail log in the black box and/or in the PF status. Is it normal? Do you have any explanations?
Regards,
Stephane