Hello all,
I have a BQ40Z60 EVM and the schematic seems to have reverse polarity protection (implemented with Q4 and Q6) for the AC charger input voltage. I would like to add AC charger overvoltage protection to this, because my application needs to survive up to 50 volts on the AC charger input. Can I use Q6 for this? Becaue the BQ40z60 pulls the gate of Q6 low when the AC input voltage exceeds the configured maximum, I figured that I could use this to protect the BQ40Z60 and the charger stage from AC input overvoltage.
For Q6 to work as overvoltage protection, the mosfet needs to be flipped aroud (D and S swapped), otherwise the body diode would continue to conduct, even if the BQ40Z60 turns the MOSFET off.
I have some more questions:
- Why is Q6 being driven by the BQ40Z60 on the EVM, if it's only job seems to be reverse polarity protection?
- can I add another MOSFET in series with Q6 in a back to back configuration (drains connected together) to add overvoltage AND reverse polarity protection?
- Is the ACFET output fast enough to function as overvoltage protection? If the ACFET output doesn't go low fast enough, the damage might already be done...