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BQ25896 IINDPM problem

Greg Smith80
Prodigy 30 points
Other Parts Discussed in Thread: BQ25896

I've got a system running with the BQ25896, with a 180 ohm resistor on ILIM pin (max input 2.16 amps.)

I'm finding that the Reg 13 IINDPM bit is getting set at unexpected times.

For example:

- set fast charge current ICHG to 1.536 amps

- system load is about 300 mA

- battery charges fine. Internal A2D confirms 1.5 amps going to battery

- voltage on ILIM pin is 0.7v, indicating input current is about 1.9 amps as expected, and under the ILIM limit

- regardless of what I set the IINLIM reg to, I'm getting the IINDPM bit go high somewhere around 1.7 amps

- even when the IINDPM bit is high, it still charges at 1.5 amps as expected. DPM doesn't doesn't reduce it

If I lower the charge current to 1.25 amps, its all happy.

I've tried setting IINLIM to lots of different values, including 63 (max.) Low values change the behavior it but not values greater than about 1.7 amps.

I've tried ICO_EN enabled/disabled, AUTO_DDPM_EN enabled/disabled, relative/absolute DPM, nothing helps.

I'm using the data sheet  "July 2015 - revised September 2015" which does have a number of typographical errors in it. Maybe a later version clarified/fixed something?

Thanks.

 

  • 0
    TI__Guru**** 167196 points
    I assume you have REG08 bit 6 EN_LIM bit high and PSEL pin tied low. If so, then the maximum input current allowed is the 2.16A set by the ILIM resistor. IINMAX = KILIM/RILIM where KLIM = 320 to 390 Aohm. With RLIM = 180ohm, INMAX is the range of 1.78A to 2.16A. The IC you have must have KILIM on the low side and with your loading, you are entering early IINPDM as reported by the IINDPM bit. The integrated 7-bit ADC is likely not precise enough to report the slight decrease in charge current. Do you have another method to measure charge current?
  • 0 in reply to Jeff F
    Prodigy 30 points
    Thanks, OK this makes sense. I didn't take into account the tolerance on KLIM for my resistor calc.
    I can measure the charge current, but I know what I need to do to fix anyway (adjust the resistor to 2 amps for the worst case.)