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BQ24079: precharge behavior with Vbatt<1V

Gary Box
Prodigy 135 points
Part Number: BQ24079

What is the expected behavior of the BQ24079 precharge current with the battery voltage below 1V? I'm seeing two scenarios over a population of 14 units. charge current is set to 100mA.  In about half, the precharge current falls to 0 at about Vbatt=750mv. In the other half, it rises from 10mA to 55 mA between Vbatt =2.4V and Vbatt= 750mV, then goes to 0 between Vbatt=750mV and Vbatt=200mV, then jumps to 60mA between Vbatt=200mV and Vbatt=0V. See below. Which of these scenarios is normal? The datasheet gives no precharge/ Vbatt information.

  • 0
    TI__Guru 67476 points
    Hello
    There is a problem with the attachment, could you post it again?

    If battery voltage is below 1.8V the current is limited to 7.5mA, short circuit detection.
    Between 1.8V and 3.0V the current is limited to pre-charge, 10% of the fast charge current set by ISET.
    Above 3.0V current at the fast charge rate set by ISET.
    When battery voltage reaches 4.2V current will begin to decrease, taper.

    Also check setting of EN1 and EN2,
  • 0 in reply to Bill Johns
    Prodigy 135 points

    One of the assemblies I have exhibits that behavior. Seven others exhibit close to the current limited short circuit detection value down to a battery voltage of about 750mV, then no current below that. Six exhibit the attached behavior. Are the 13 damaged?

    Vbatt Iprecharge
    0 61.5
    0.1 61.6
    0.2 61.14
    0.3 0
    0.4 0
    0.5 0
    0.6 0
    0.7 0
    0.8 0
    0.9 58.4
    1 56.4
    1.2 51.7
    1.4 45.9
    1.6 38.8
    1.8 32.2
    2 23.2
    2.2 14.2
    2.4 10
    2.6 10
    2.8

    10

     

  • 0 in reply to Gary Box
    TI__Guru 67476 points
    I checked and EVM board in the lab, set it up for 100mA fast charge current.

    Above 3.0V battery voltage charge current is 100ma
    ---Voltage on ISET Pin 2.225V
    Below 3.0V battery voltage charge current is 10mA
    ---Voltage on ISET Pin 236mv
    Below 1.8V battery voltage charge current is 7.5mA
    ---Voltage on ISET Pin 6.8mv

    The transition point is pretty accurate, 3.0V and 1.8V.