Hello, I'm facing a strange BQ24616 behavior when trying to charge li-ion cell pack.
The setup:
- 6 series li-ion cells with build-in protection - new, precharged to ~3.7V.
- BQ77PL900 AFE for ballancing (with external ballancing FETS) - tested with EV2300 (CHG and DSG FETS are working, IC is working)
- BQ24616 with a basic circuit - ISET1=1.5A, ISET2=65mA (will be cutted to 125mA - OK), ACSET=3A, VCRHG=24.6V (4.1x6), System Load < 100mA
- External power - 28V regulated lab power unit
All cells are in place, BQ77PL900 is active. When turning on the external power or toggling CE there is no activity on PH, HIDRV, LODRV, however:
- nPG is low which means that BQ24616 passes power test, VCC=28.2V
- STAT1 and STAT2 are off (hi-z)
- VFB=1.86V, VBAT=21.9V
- VREF=3.3V, REGN=6V
- TS = 2.02V
- LODRV=0v, HIDRV=21v
- ISET1=300mV, ISET2=65mV, ACSET=610mV - as expected
- nBATDRV is also working: when AC on nBATDRV=28V, when AC off - nBATDRV=16V
What tests were done:
- Tried to short AC sense resistor - no change (after toggling CE)
- Tried to short TTC cap - no change (after toggling CE)
- Tried to short CHG and DSG FETS of BQ77PL900 - no change
- Tried to discharge cells - VBAT dropped from 21.9V to 20.8V - no change (after toggling CE)
- Tested charger PCB against shorts and line breaks - no problems detected
Then I've replaced each cell with a 180 Ohm resistor:
The BQ24616 started to work: HIDRV was toggling fast, PH was toggling also, on VBAT there was a ramp repeating each ~160ms (can't attach osc pictures now). STAT1 and STAT2 were OFF. Tried to short PTC to gnd and after CE toggle the BQ4616 stopped working as expected.
So I gently assume that BQ24616 logic and charger circuit are working and components are pretty alive.
But what stops BQ24616 when I try to charge a pack in place?