Hello,
I am looking for some direction in diagnosing a custom PCB using the BQ25731.
The issue I am having is upon switching startup to charge the attached battery the input voltage spikes drastically above the supply voltage for a significant amount of time. See the below VBUS trace (Yellow) with respect to the Q4 MOSFET (Blue).
VBUS spikes from 5V to 9.4V over 5ms. I have seen spikes up to 23V from a 5V input from multiple sources.
My hardware configuration:
- The BQ25731 is setup in its 400kHz using a 4.7uH inductor and all of the recommended compensation component values.
- The BQ25731 has a 14.6V nominal 4S battery that it is charging.
- I have 134uF of effective capacitance on the VBUS side of the BQ25731 accounting for DC bias of the caps I have chosen.
- I have 156uF of effective capacitance on the VBAT side of the BQ25731 also accounting for the DC bias of the chosen caps.
My register/firmware configuration
- All POR default settings.
I seem to get the max voltage spike of 23V consistently when switching starts by toggling the CHRG_INHIBIT register with the 5V already plugged in.
I can provide schematics/design files if we can move this to a non public thread.
Thanks,
Nate
