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BQ24707A: ACOK Function

Alex Fields
Prodigy 90 points
Part Number: BQ24707A

Hi, I am very confused with the ACOK function of the BQ24707A. Please let me know if I have this correct:

a voltage above 0.6V on the ACDET pin wakes up the ACOK comparator as noted on the datasheet, but a voltage of 2.4V is needed on the ACDET pin to enable a charge.

Now, they say pick a resistor divider such that the voltage on the VCC pin is higher than the max battery voltage, but lower than the input voltage of the charger. Should you pick this resistor divider such that its threshold is 0.6V, or 2.4? Why are there 2 thresholds? E.g. we picked a threshold of 15.6V, and had a 300k to 12k resistor divider, so ACDET > 0.6V when VCC > 15.6, but this doesn;t seem to enable charge. Should we have picked a voltage divider such that ACDET > 2.4V when VCC > 15.6? Then what is the use case of the 0.6V?

Thanks,

Alex

  • 0
    TI__Expert 5330 points

    Hi Alex,

    Yes, please adjust the resistor divider so that the 15.6V point divides down to 2.4V.  (replacing 12K resistor with 51K or 56K should give you approximately the trip point you are looking for.)

    Crossing the 0.6V threshold allows some internal circuitry to be powered and turned on, including the actual ACOK comparator.  But only crossing the 2.4V threshold will cause the ACOK comparator to trip, which will transition the ACOK pin to high and will turn on the ACFET/RBFET to pass the adapter power through to SYS and the charging circuit. 

    Regards,

    Steve