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BQ2973: battery first connection behaviour

TomokiP
Prodigy 20 points
Part Number: BQ2973


I am developing a board using BQ29733 battery protection IC in standard configuration (as in datasheet, with the only difference that I added a 5Mohm resistor between GS of each MOSFET).

When connecting battery for the first time, I would like to have the discharging circuit disabled until charger is connected to its terminals.

From our tests on a few boards, it seems like this behaviour is always obtained: however, from the datasheet it seems like a possibility since "the discharging circuit might not be enabled" (see below image).

Since we would like to rely on this feature, is this behaviour confirmed? What does this behaviour depend on?

Does the standard configuration need any modification in order to ALWAYS obtain such behaviour?

Thank you very much for the support.

Best regards,

Tomoki

  • 0
    TI__Expert 8526 points

    Hi Tomoki,

    When the battery is being connected (CELL+/CELL-), keep PACK+ (V+) and PACK- (V-) shorted together, and that should ensure the device remains in shutdown mode at initial connect.

    Best,

    Andria

  • 0 in reply to Andria McIntyre
    Prodigy 20 points

    Dear Andria,

    thank you for your reply. We would like to avoid shorting PACK+ and PACK- as the main board is not powered at initial connect.

    However, by triggering the undervoltage protection of the BQ9733 it seems to be possible to connect the battery without powering up the board from it. In order to do so, we would like to increase the time constant of the RC circuit at the at BAT and VSS pins (see image below).

    By making sure that the time constant is well above the UV detection delay time, do we achieve our desired behaviour (i.e. board not powering up at initial battery connect but instead powering up once charger is connected to battery pack)?

    Best regards,

  • +1 in reply to TomokiP
    TI__Expert 8526 points

    Hi Tomoki,

    As an addition to my earlier answer, I would like to say that the solution regarding shorting PACK+ (V+) and PACK- (V-) together is the only way to absolutely guarantee that the device will start with DSG off, but even without this, the device should start with DSG disabled during initial cell connect. 

    As for altering the RC time constant: That should work, but it may alter the noise filtering profile, so be mindful of that.

    Best,

    Andria

  • 0 in reply to Andria McIntyre
    Prodigy 20 points

    Everything clear!

    Thank you Andria for your kind support.

    Best regards,