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BQ25890: potential charging issue and interrupt flood after 'termination-done' is received

Laurentiu Palcu
Prodigy 20 points
Other Parts Discussed in Thread: BQ25890

Hi,

I'm having 2 potential issues with BQ25890 charger chip and I'd like to understand what's going on. Maybe I'm doing something wrong...

Here's my setup:

  • BQ25890EVM board;
  • Li-Ion cell, connected on J4;
  • electronic load (EL), emulating the system, connected on J3;
  • USB wall charger (5V - 2A), connected on J5 (both S2 microswitches ON);
  • ampere-meter in series with the battery; 

The issues I'm seeing:

  1. if the EL is not turned on and the USB charger is inserted, I'm seeing a current of about 100mA going to the battery (battery is almost full, so it's fine). However, turning on the EL I'm seeing the following charging currents for different EL current draws: 200mA(EL) -> 100mA(bat), 500mA(EL) -> 20mA(bat), 800mA(EL) -> -200mA(bat). So, with the charger inserted and a consumer that draws 800mA, your battery actually discharges? STAT pin is low though! Is this normal? The wall adapter is supposed to be able to provide 2A of current, yet only 600mA are drawn from the wall adapter, the rest is from battery. Am I missing something?
  2. when 'termination-done' comes, I'm starting to see a flood of interrupts with CHRG_STAT toggling from 0x2 (fast-charging) to 0x3 (termination-done). If I set CHG_CONFIG=0, the interrupts stop since the charger is disabled. However, if VBAT falls below VRECHG threshold, the charging is not started automatically. So, how do we start a new charging cycle?

Thanks.

  • 0
    TI__Guru**** 166996 points
    Please short out the ammeter and see if operation improves, especially the issues in item 2. Ammeters in series with autorange enabled cannot be used. Even with autorange disabled, the extra series resistance can cause issues.

    What is the off state of the EL, high impedance or low impedance? Is the current going into or out of the battery? If the input current limt is too low to support the system load, then the IC supplements the system load from the battery.
  • 0 in reply to Jeff F
    Prodigy 20 points

    Hi Jeff,

    You were right about the ammeter. Indeed, after removing it from the circuit, I got just one interrupt for 'termination-done'. So this solved issue 2.

    Regarding issue 1, I just read the documentation again and found out that I had ILIM pin activated (EN_ILIM = 1). So, ILIM pin was limiting the input current. I deactivated it and the behavior was as expected.

    I have another question though. Currently there's no interrupt fired when going back to "fast-charging" mode, after VBAT falls bellow VRECHG? Unless the host monitors also the STAT pin (which might not be the case for all hosts). Was this intended? Or am I missing, again, something from the documentation? 

    Thanks.

  • 0 in reply to Laurentiu Palcu
    TI__Expert 5565 points

    The device does not send an interrupt when entering fast-charge mode. If you have the full datasheet for this device, you will find the conditions where INT is toggled listed on the bottom of page 26 (section 9.2.9.3).

    STAT will only tell you when charging has started (for example, when VBAT falls below VRECHG), but it will not indicate when you go from pre-charge to fast-charge.