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BQ40z50 Pack Pin

David Thompson2
Intellectual 685 points
Other Parts Discussed in Thread: BQ40Z50

Hi,

Is the PACK connection to the BQ40z50 used for anything other than getting the device out of shutdown mode? I'm wondering if I can put a FET in-line with the pack connection to the BQ (between BQ & P+, not between P+ and the DSG/CHG FETs). If I can do this, I can use a processor to control when the pack wakes up, rather than have it automatically wake as soon as voltage appears on P+.

Obviously a FET would drop 0.7-1.5V so the pack voltage measurement would be inaccurate but that wouldn't be an issue for my application, provided I can be sure the PACK measurement is not used for anything other than wakeup.

Thanks

  • 0
    TI__Guru 73830 points
    The Pack pin voltage is also used as the reference for the DSG FET charge pump, so I would be mess with it. I would let the gauge wake-up when voltage is applied. If the concern is keeping the FETs off, then you can use the PRES/ pin to control them. Pull it high and they will turn off. Pull is low and the gauge will control the FETs.
  • 0 in reply to ThomasCosby
    Intellectual 685 points
    Thanks for the reply. That's not what I was hoping for, but at least it means I don't have to faff with the complicated solution I had in mind.
    I was preferring that the whole pack be in shutdown mode when it's not in use, as that consumes about 50uA less than just having the FETs off in sleep mode and would give the pack a substantially longer shelf-life. However, my other reason was that I wanted to use the P+ connection of the pack for another purpose while the gauge was in shutdown which would require a voltage to be applied to the P+ pin. It seems that I can't do that because as soon as I put a voltage on P+ it will wake everything up... (there is too much overlap between the voltage I need to put on it and the minimum charging voltage)

    I'll have to go with plan B (whatever that is...)

    Thanks