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BQ2002T VBAT threshold error

David Mittmann
Prodigy 130 points

I have a circuit just like http://www.ti.com/lit/ug/sluu007b/sluu007b.pdf using 4 cells.  Pin voltages are DC as follows:

1=2.5V, 2=0V, 3=2.1V, 4=0V, 5=1.61V, 6=5V, 7=0V, 8=4.3V

Can anyone think of a reason why the CC pin 8 is in high impedance when the VBat pin 3 is above 2.1V?

I must be missing something here.  The batteries start off fully charged so they are above 2V and do not  cross the 2V level. Is the 2.1V in the tolerance range of the chip?

Thanks

  • 0
    Prodigy 130 points

    I think I figured out what the problem is. The inputs of Vbat and Vts need to be stable and within range before VCC goes up.  If I delay VCC the chip behaves according to the datasheet.  I confirmed this by bread boarding the chip and supplying independent voltages to each pin using bench top voltage supplies.  If VCC goes high with VBat and VTS still changing it can get into a weird state and stay there forever without timing out.  The state can have CC pin high, or low.  But when I disconnect the supply to VCC and let all other pins turn on, then connect VCC everything works correctly. Alternatively I just put a large RC filter on VCC to have a long rise time for VCC then the chip also works.