MP2759A: STAT Fast pulsing

Battery Management
1

Hi,
We have designed a 4S2P battery charger using the MP2759A charger IC combined with a TI BQ77915 Monitor IC.
Number of Cells: 4
Cell voltage: 4.2v (16.8V pack voltage)
Charge Current: Set for approx. 2.8A
The charger starts to charge at 2.8A but then the current drops to 20mA {nominal load) and the STAT pin pulses at 8Hz as shown below. Includes schematic.

BatteryChargerSchPlusScope
BatteryChargerSchPlusScope2044×1782 434 KB

If I connect the load, which is minimal around 30mA the battery charge is stable util the battery voltage increases to a point where the pulsing starts again and the battery no longer gets a charge current even though the battery is not fully charged.

What could cause the STAT pin to pulse.
Note: If I remove the NTC, the charger IC STAT pin blinks at 2Hz error rate.

Any help would be appreciated.
Thank you
Regards
Carl

2

Well who knows? Can you get rid of the BQ chip that might be disconnecting on its own for its own reasons? Maybe the MP part isn’t to blame

3

Thank you for your reply JShannon.
I did think about that, but after I posted.
I bypassed the FET’s and it looks to be functioning correctly. Just wasn’t sure when it was doing a fast pulsing on the STAT pin.

4

Hi Carl, I am currently facing the same issue as you. The STAT LED is blinking at 8 Hz.
Could you let me know which FET you are bypassing?

Any advice would be appreciated. Thank you