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BQ25890: BQ25890 Maxcharge, HVDCP, ilim battery charge current question.

Jared Mizrahi
Prodigy 125 points
Part Number: BQ25890

Dear Support,

I have a question pertaining to the BQ25890 and the ilim hardware pin. I have a current design where the microprocessor is not required to be on to charge the device. Under this scenario I was relying on the hardware ilim resistor to limit the battery current. By default and watchdog reset, the BQs charge current default is set to use 2 Amps to charge the battery. This is a little too high for my application. I had sized the ilim resistor to prevent charge current from being too high for my particular battery assuming a typical 5V USB input. With maxcharge and HVDCP enabled by default, will I have a potential problem if a high voltage charger is used prior to the microprocessor being turned on for the first time, or after a power on reset due to a battery swap?


For example. With an ilim set to a maximum input current at .9A on a 5V input power there is 4.5W of charging power. Assuming perfect efficiency and the battery has just left pre-charge state, this is still below my battery’s charge limit. However, If maxcharge or HVDCP are negotiated, the power may go up to 10.8W.

Am I correct in assuming that this higher power converted to charge the battery may be an issue, if the processor has not yet lowered the fast charge current registers?


-Jam

  • 0
    TI__Genius 10240 points
    Your concern is valid since the ilim does not have the input voltage information. You already commented that the processor could reduce the charger current setting and you need the processor to adjust the the charger register. Another option is to use bq25890H, which is HVDCP or MaxCharge detection disabled by default REG01[1]=0. It requires processor to enable the detection. Please also check REG01, REG0A[3], REG0D[7], REG14[0:1], V(OTG_BAT) and TQON_RST for the difference of bq25890H over bq25890.
  • 0 in reply to ezhao
    Prodigy 125 points
    Hi ezhao,

    The field in REG01[1]=0 disables the 12V maxcharge and HVDCP, but does not mention the 9V setting. However, by adjusting the ilim R value, I think I can use the BQ25890H version with minimal circuit changes. This should lower the charge current going into the battery to a safe level. Thank you for this suggestion.

    Additionally, It seems there are a few BQ24XXX series ICs that have very similar pinouts, but do not support higher voltage charging. These ICs seem like they could work as well.

    -Jam