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BQ25700AEVM-732: Battery isolation in BQ25700A reference design

Clancy McColl
Prodigy 10 points
Part Number: BQ25700AEVM-732

I am after some technical assistant with the following reference design,
https://www.ti.com/lit/ug/sluubg6/sluubg6.pdf?ts=1630994554534&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ25700A
I'm a little confused how the P-Channel mosfet can disconnect the system from the battery. I have simulated that and it seems like power can always flow from the battery through the body diode to the system, but in the data sheet it says it can disconnect the battery from the system. Just using the schematic in my design and trying to understand that part of the circuit. Document: SLUSCQ8A –MAY 2017–REVISED MAY 2018, section 8.3.1 on page23. The main thing I am trying to confirm is whether this reference design will shut off from the system when the batteries are depleted.

Cheers. 

  • 0
    TI__Genius 11385 points

    Hi Clancy,

    You are absolutely right. There is no way for the charger to shutoff the discharge path from battery to VSYS. Even if the BATFET is turned off, power can still flow from battery to the system through the body diode. Typically, user would have a battery gauge/monitor/protector on the battery side to shutoff the discharge path.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • +1
    Prodigy 10 points

    Yeah thanks for that, 

    Another couple question came up today,

    what's the intent for cmp_in and out? 

    And is the current measuring on the battery interface good to monitor the discharge of the battery to indicate how much charge is left in the battery?

    Cheers Clancy. 

  • 0 in reply to Clancy McColl
    TI__Genius 11385 points

    Hi Claney,

    CMPIN and CMPOUT is a set of independent comparator that user can use for their own application. 

    On battery state of charge, the gauge products/ICs should have dedicated status reporting. User does not typically have to do that themselves.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory