I'm working with the bq24650 in order to charge a 12V 9AH Lead Acid battery. I have designed my circuit according to the SLVA237A app note and the part datasheet. Some design points are as follows:
- Vinput = 15.6V
- VMPPSET = 13.33V
- R17 = 364 kOhm and R19 = 36 kOhm (R17 and R19 are based off app note)
- Vblk = 14.7V
- Rsr = 0.04Ohm
- 1A charge current
- Vrech = 13.8V
Note: this design does support temperature compensation.
I'm attaching an oscope measurement taken during the charge cycle. The blue is the charge current, the yellow line is Vcc, and purple is SRN.
I've drained a battery down to about 10.6V and have connected it to the charger. The charger will apply about 970mA of current, but this amount will decrease slowly over the course of the charge. Note I am measuring this current across the sense resistor. The current starts to decrease once the battery is around 11.8-12.2V, not at the expected Vblk amount, where the current should rapidly decrease. I've spoken to several TI employees on this already, but none could give me an explanation so far, so I'm hoping to get help here.
Thanks for your help.
