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BQ51051B: Minimising quiescent power consumption?

Edward Colby
Prodigy 30 points
Part Number: BQ51051B
Other Parts Discussed in Thread: BQ51013B

Hi

In a design migration we've moved from the BQ51013B to BQ51051B. What has been disappointing is the quiescent current that the BQ51051 draws. Our application aims to get months of battery life from a 240mAh LiPo and the data sheet minimum quiescent of 12uA represents a massive amount of our power budget. This seems like a pretty fundamental design consideration for a battery powered system - surely you'd want the charger to consume as little power as possible when not charging the battery.

In the BQ51013B design we had a separate charge controller and this prevented the battery back powering the Qi chip. Not an elegant solution, but it did achieve very low quiescent draw.

Is there any reason to keep the BQ51015B connected to the battery when wireless power is not available? I guess ideally for us the chip would only take power from the Qi link and be disconnected from the battery when the link isn't present.

We're toying with the idea of putting a FET between the BQ51051B and battery, the FET switched from the RECT terminal of the chip. Would this work? We've discounted the idea of putting a simple diode between the BATT connection and battery - presumably the charge controller wouldn't like that, but would a FET be just as bad?

Perhaps we're mis-understanding how to use the chip properly. Any thoughts / insights would help.

Thanks

Ed 

  • 0
    TI__Mastermind 23410 points

    Hi Ed,

    Sorry to hear your frustration with the quiescent current on the BQ51051. Can you share what value you're measuring on the quiescent current? Is it preferred to not have to use a separate charge controller? We have a few chargers that pair with the BQ51013B that feature low Iq modes -- some in the nA range.

    A diode is not preferred as the voltage drop from the BQ51051B to the battery can't be accounted for in any way. A FET would be a workable solution. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 30 points

    Hi Anthony,

    Thanks for the insight.

    We were previously using a BQ51013B and separate charger, we swapped because we were short of board space in the new design. Removing everything else from the board bar the BQ51051B circuitry and passives we get 13uA draw from the battery - this seems in line with the data sheet.

    Understood re. diode and FET. We'll have a go at prototyping something around the FET whilst considering body diodes carefully.

    I suspect that the right thing to do is to seek out a charge controller in a small package, to try to claw back a little board area and to revert to the '13 design.

    Thanks again

    Ed