Good Morning,
I have a customer with the following question:
"Our protection circuit board is using a bq29412 to sense cell voltages as a secondary protection device. The output of that chip drives a FET, which in turn pulls the PFIN input on the bq20z95 to ground. The PFIN input is normally pulled to 2.5V using the built in regulator from the bq20z95 chipset.
XPFIN in the Permanent Fail Cfg is set low, so the PFIN failure does not activate the SAFE output of the bq20z95, if I am understanding the technical reference correctly. There is a chemical fuse in line with the output which, in the case of a PFIN detection, is pulled low through the same FET as the PFIN input pin, causing the fuse to open.
When I reviewed the PF Status data from flash settings on the battery, it showed the highest cell voltage at 4159mV. The bq29412 circuitry is configured to drive the PFIN FET if any cell reaches a maximum voltage of 4450mV for 1.67s. PF Detect Time is set for 5 seconds.
My question is, how long does it take between the time that the PFIN permanent fail is set and the PF Status data is read from the bq20z95?"