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Unpowered BQ77PL900 Cell drain?

Sebastien Bourdage
Intellectual 330 points

Other Parts Discussed in Thread: BQ77PL900

Hello,

Would unpowering the BQ77PL900 (switch that cuts off BAT and rest of the system) while leaving the cells (VC1 through VC11) connected cause any harm to the BQ77PL900 or significant drain through the cells?

Thanks,

-Seb

  • 0
    TI__Guru 54715 points

    The situation described is anticipated as a transient event during cell connection and should not destroy the device.  Note that absolute maximum is expressed in volts to GND rather than between VCx and BAT.  However the recommended operating conditions indicate the VC1 - VC10 should be between 0 and BAT.

    The electrical parameters are based on normal operation with BAT in the range shown in the tables.  VCx input current is not shown in the tables, it is likely to increase if BAT is not applied since there may be abnormal bias paths.

    The recommended method to reduce supply current while keeping the device in its recommended bias condition would be to place the part in shutdown mode.  Note that ISHUTDOWN is much less than ICC. This would be achieved with a command sequence in host mode.  In standalone mode shutdown comes from UV, one of the safest ways to achieve this may be to disconnect the top used VCx pin and pull it gently to the VCx+1 pin with a switch.  This should keep all inputs within recommended and abs max limits.

  • 0 in reply to WM5295
    Intellectual 330 points

    Ok thanks. I'll give that a try.