Other Parts Discussed in Thread: BQ24630,
On a working design we're changing from a LiFePO4 pack to a Li-Ion pack and was told to swap the BQ24630 for a BQ24610. I also changed the VFB R ratio to set the charge voltage to 16.4V (with a 18V Vin). I understand that I'm pushing the 1.5V - 2V headroom. I believe these are the only changes needed since the only equation that changes is the VFB voltage (and the pack voltage). Please confirm. But the results baffle me - instead of ~2.1V on VFB I have 6.5V (with a 15V nominal pack) using a 909K/133K divider. Just to make sure, I had both resistors and the BQ24610 replaced, but got the same results. I see no solder bridges or other issues on the board. I find it hard to believe this issue is caused by my skimping on the headroom.
So I dropped the R divider to 110k/16.2K to see if it was a leakage problem and now VFB does track the pack voltage correctly! The chip says it's now charging (via the Charge LED), but the pack voltage does not increase and no current is being drawn from the 18V supply so no charging is happening. The charge current is set for 1.5A.
If I unplug the pack, many strange things happen. The ACDrv signal has a waveform on it so the system keeps resetting due to transient loss of power. There's also a waveform on BatDrv. Any observations or suggestions?
