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BQ24725 - Can I choose to power the system from the battery - even when the AC adaptor is present?

David Kemp
Prodigy 120 points
Other Parts Discussed in Thread: BQ24725

Hi guys,

I'm looking into the BQ24725 battery charger and was wondering if I could choose to power the system from the battery even when the AC Adaptor is present. (not while charging) 

From what I gather this is not directly possible from accessing control registers via the SMBUS. I see that we can disable the charging function - but the system will still be powered from the AC adapter as long as it is present. Is this correct?

If this is correct, can I assume that the only way to accomplish this task is by controlling the voltage on the ACDET pin? For example (Figure 2 BQ24725), could I add  FET/RESISTER (in series) parallel to R2 such that when the FET is on,  the voltage at ACDET is reduced and the battery is chosen to power the system instead of the AC (by fooling the chip into thinking the AC adaptor voltage is invalid). Is this a practical solution?

Are there a similar TI chargers that have this functionality?

 

Thanks 

  • 0
    TI__Guru 56650 points

    On bq24725 datasheet page 17th, the "Learn Enable" control bit can "choose to power the system from the battery even when the AC Adaptor is present. (not while charging) ".

  • 0 in reply to Wang5577
    Prodigy 120 points

    Is there no downside to using the LEARN function to accomplish this?

    According to the datasheet the LEARN function is intended to do the following: 'LEARN function allows the battery to discharge in order to calibrate the battery gas gauge over a complete discharge/charge cycle.'

    alternative. Is this the way TI recommends?validI suppose the learn function can always be interrupted at will, so maybe this is a

  • 0 in reply to Wang5577
    Prodigy 120 points

    Is there no downside to using the LEARN function to accomplish this?

    According to the datasheet the LEARN function is intended to do the following: 'LEARN function allows the battery to discharge in order to calibrate the battery gas gauge over a complete discharge/charge cycle.'

    I suppose the learn function can always be interrupted at will, so maybe this is a  valid alternative. Is this the way TI recommends?

  • 0 in reply to David Kemp
    TI__Guru 56650 points

    I didn't find any downside of the LEARN function. The datasheet gives an application example: LEARN function allows the battery to discharge in order to calibrate the battery gas gauge over a complete discharge/charge cycle.

    I would recommend this LEARN function.