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BQ24250: BATFET off do not seem to work

M.A.M
Expert 8795 points
Part Number: BQ24250

Hi,

My customer try to turn off BATFET via I2C Register#2 Bit 1 "CE" so that they can measure system current from input. This does not seem to work. Is there some other trick to know? Their HW pin CE is tied to GND via 100K.

Thanks.

B.r M.A.M

  • 0
    TI__Guru**** 166006 points

    Hi M.A.M,

    The BQ24250 SYSOFF requires the bit to be set and then input power removed for the BATFET to turn off.  It is a true "shipmode" as compared to our other devices that allow you turn off the BATFET any time you want.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    TI__Expert 8795 points

    Jeff,

    So it means that the customer cannot measure system consumption, without battery charging ongoing in parallel.

    Please clarify, thanks.

    /M.A.M

  • 0 in reply to M.A.M
    TI__Guru**** 166006 points

    Hi M.A.M,

    Correct.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Expert 8795 points

    Jeff,

    We need to be 100% sure. The term SYSOFF that you mention is associated with Register #6 Bit 4  "SYSOFF"(section 9.6.6) , however the datasheet still in section 9.6.2 describe for Register #2 Bit 1 "CE" and the footnote below, that this BATFET off functionality exist.

    - Can you confirm that the datasheet is wrong regarding the ChargeEnable register bit functionality?

    Thanks again.

    B.r M.A.M

  • 0 in reply to M.A.M
    TI__Guru**** 166006 points

    Hi M.A.M,

    The /CE pin turns off BATFET current flow from SYS to BAT for battery charging.  It does not turn off current flow from BAT to SYS for supplement mode, for example if the SYS load is more than the input power source can provide.  Therefore the BATFET cannot be 100% turned off using /CE pin.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Expert 8795 points

    Jeff,

    I do not get it.. This is exactly what they want, stopping charging current from SYS to BAT.

    The only difference is that you talk about the /CE pin. They tied this to GND via 100K, but instead want to set the Register 2, Bit 1 called "/CE" to '1' by software.

    - Can they stop charging current flow from SYS to BAT under this condition?  or will the physical /CE pin override the register bit if the pin is tied to GND?

    B.r M.A.M

  • 0 in reply to M.A.M
    TI__Guru**** 166006 points

    Hi M.A.M.,

    /CE pin pulled high OR CE bit = logic low turns off charge, in other words, turning off charge (current flow from SYS to BAT) always takes precedent.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Expert 8795 points

    Jeff,

    Are you sure about the register bit polarity?

    Datasheet say for /CE bit:

    "0 –Charging is enabled 1 –Charging is disabled"

    Please clarify.

    Thanks.

    B.r M.A.M

  • 0 in reply to M.A.M
    TI__Guru**** 166006 points

    Hi M.A.M,

    You are correct.  This charger, unlike most of our other chargers, has /CE bit not CE bit.  So, to disable charge, /CE bit =1.

    Regards,

    Jeff