BQ24780S: Battery FET

Hugh Bisset1

Part Number: BQ24780S

Hi,

Please see diagram in datasheet below. The application I am working on does not need SYS to be supplied by the battery, when the power adapter is off even if the battery is still connected the product should be off. In that case can I remove Q3, R12, the 4.02K resistor on BATDRV pin, D1 and D2. This will mean that VCC will only ever get power from the adaptor and there is nothing connected to BATDRV and BATSCR.

Thanks

over 4 years ago

0 Hugh Bisset1 over 4 years ago

Prodigy 80 points

0 Steve Preissig over 4 years ago in reply to Hugh Bisset1

TI__Expert 5330 points

Hi Hugh,

You may remove the Q3 BATFET. If so, please leave R12 in place with BATSRC connected as normal at the inductor output. You may remove the 4.02 kOhm resistor from BATDRV and leave it floating.

As you say, you may remove the D1 and D2 diode-OR and power VCC off of the adapter input only since you do not need IC functionality without adapter attached.

Assuming you don't have a power source at SYS (other than the adapter), you can also remove the Q2 (reverse blocking FET.) The purpose of this FET is to keep BAT voltage from going across the body diode of the Q3 BATFET and propagating out to the connector. Since you don't have a BATFET, that can't happen.

Regards,

Steve

0 Hugh Bisset1 over 4 years ago in reply to Steve Preissig

Prodigy 80 points

Thank you Steve. This resolved my issue.

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BQ24780S: Battery FET