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want to charge a 3.7 V 2200mAh Li ion battery with a BQ24650

naga raja
Prodigy 80 points
Other Parts Discussed in Thread: BQ24650

Hi 

1)How can the VFB value be kept constant in a BQ24650.  

2)Changing the voltage divider resistors R1 and R2 also changes the VFB.

3)I want to charge a 3.7 V 2200mAh Li ion battery.

4)When R1 - 191K  R2 - 100K  VFB was 1.05 and VBAT was 3.05. So when I changed R1-191K and R2-75K so that to obtain VBAT - 3.7 but VFB got changed to 0.86 now! 

I used the formula

VBAT=VFB*(1+(R2/R1)).

What voltage divider resistor should i use to charge the battery now.kindly give suggestions

  • 0
    TI__Mastermind 31120 points

    Please check with the battery manufacturers data sheet about the regulation voltage of the battery.

    It is most likely 4.2V, but please verify.

    Set both feedback divider resistors to 100k.  When the converter charges the pack to 4.2V the divider value will be 2.1V which is where the internal op amp reference is set.  The converter will regulate at output voltage at this time and the current will taper off.