Tool/software:
Hi all,
We are having this design for a 50W 4S li-ion battery charger and we are experiencing an issue where plugging in the battery sometimes causes the system to fail short. In particular the U1 (BQ24610) and the low side MOSFET Q4 fail short. Together with this, the battery fuse F2 fails open. When this happens, you can see a spark flying off the fuse.
This doesn't happen always but only in maybe 10-30% of battery inserts. It never happens with a power supply and less prone to happen when the battery is discharged. The most severe issue is when the high power battery is fully charged.
Here is the circuit:
The current theory is that the system turns on the low side MOSFET Q4 while inserting the battery and this then saturates the inductor and this breaks the fuse F2 and then the induced voltage breaks the parts it is connected to.
I have captured the moment of inserting the battery and you can see that it in fact does turn on the low side MOSFET on the following image where the blue trace is the battery and red trace is the gate of Q4. The timebase is 500us/div.
We are currently experimenting with a high inrush current fuse but it is not clear yet if this can fix the issue. Another thing we are looking at is to use a MOSFET with a higher gate threshold.
Can anyone shed any light on this and propose a potential solution?
Kind regards
