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BQ77908 Using identical circuit as EVM, removing power from BAT pin, load continues to draw current/operate

ANDREW PARKER
Prodigy 35 points
Other Parts Discussed in Thread: BQ77908A

Hello all!    I am using the BQ77908A multi-cell Li-ion protector IC.

Need help urgently with an issue regarding battery management circuit roughly identical to BQ77908AEVM circuit. With  CHGST held somewhat high using resistor divider, and while load (motor) is operating normally(discharging), removing power from BAT results in CHG/DSG FETS oscillating on/off, with an audible high pitch sound, and allowing load to continue to operate, though somewhat inefficiently.

Shouldn't removing power from BAT pin result in an 'all FETS off' fault condition or just cease to operate?

Does the BQ77908A somehow allow itself to operate with no power on BAT line due to internal feedback of some sort?

If this is not simply silicon errata, why would this happen and what ways are there to get around it?

I am trying to simply disable the entire chip from operating, while not allowing the attached load to operate either.

Any and all advice, tips, points in the right direction, etc would be GREATLY appreciated!

Thanks all and have a wonderful evening!                         DC

  • 0
    Prodigy 10 points

    Same problem! Come on TI, little help here??? Thanks!

     

                                                                                                   Reggie