BQ2002F as a single 9V battery charger building block

Luis Olvera

Other Parts Discussed in Thread: BQ2002F, BQ2002C

Dear TI support staff,

I'm designing a single Ni-MH 9V battery charger and after searching and comparing PNs I came across the BQ2002F which seems to fit the design specs and budget. However I'm not sure if I can use it to charge a Ni-MH 9V battery. I'm not sure how to set RB1 and RB2 for my application.

Thanks and regards,

Luis.

over 11 years ago

0 Charles Mauney over 11 years ago

TI__Mastermind 31120 points

The data sheet has the formula for setting the divider. Typically one uses 1.7V to 1.8V per cell for the maximum voltage. The charger will never get to this voltage and will stay in constant current mode until termination is reached (ie do not want to get to max setting). If you have 7 cells (may be listed as 1.2x8cells = 9.6V), then the max voltage should be set to 8cells x 1.75V/cell = 14 V. You probably need at least a 16V power supply to charge this.

0 Alan Rouse1 over 11 years ago

Prodigy 60 points

The simplest way to derive RB1 and RB2 is to set RB2 = 100K and RB1 = (N-1) * 100K where N is the number of cells. Since each cell is nominally 1.25V your 9V battery pack probable contains 7 cells, so RB1 = 700K. The nearest preferred value is 680K.

0 Charles Mauney over 11 years ago in reply to Alan Rouse1

TI__Mastermind 31120 points

Thank you Alan. Alan got this formula from page 2 of the data sheet.

the note says to have a divider impedance between 200k and 1M so RB2 =100k may be on the high side (use 350k/50k).

Power management

Power management forum

BQ2002F as a single 9V battery charger building block