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BQ25180: ITERM set 5%*ICHG, the chip does not turn off battery charge when charge current reduce below ITERM

Mark Luo
Prodigy 20 points
Part Number: BQ25180

First, I plugin VIN(5v) to supply SYS(4.5v) power. ICHG is set 1000mA, the ITERM=50mA

Second, I plugin battery(4.189v), I measure the battery current, it is charging battery and the charging current is 10mA.

So the FET(Q3) does not turn off the charging process. I don't know what the chip will do when set the ITERM and the current below ITERM.

all registers values are follow

  • 0
    Prodigy 20 points

    From the datasheet, When IBAT < ITERM, it will: Charge Done, disconnect BATFET.

  • 0
    Prodigy 20 points

    I have disable VINDPM, DPPM and thermal regulation, 

  • 0 in reply to Mark Luo
    TI__Genius 13905 points

    Hi Mark,

    Typically when ITERM is set, and the device has entered CV mode, the current will drop as the battery voltage rises until current falls below ITERM. At which point charging ceases and the device. For your register set up (ICHG = 1A, ITERM = 5%) the expected behavior is termination once the current falls below 50 mA.

    Based on the register values you've provided the device appears to have terminated (REG0x00 = 0x61). You mention that even so the battery is drawing 10 mA. Can you please provide a waveform of VBAT during this time? Also, if possible, a waveform of ICHG would help in ensuring that there isn't any kind of current pulses that might be affecting termination deglitch.

    If possible, can you share the relevant schematic for your charger implementation to ensure all components are as expected?

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 20 points

    Hi , I use BQ25180EVM board, use cable to connect relate pins to our board.

    When connect 5V to EVM board's VIN, and use EVM board's SYS to power supply our board, do not connect battery, TS/MR float.

    register settings as follow picture shows, I measure VBAT, It's not stable, I don't know why VBAT cannot be stable at 4.2V.

    VBAT measure result as follows.

    Then I connect battery, there is a fuel gauge chip(max17260) between EVM board VBAT and battery cell, the schematic as follows show:

    when battery capacity not full, the result is correct:

    VBAT is stable

    but when battery nearly full charged, the charge current will below 50mA, and VBAT will not stable, and the charging state switches frequently, from charging done to cv charging or to cc charging.

    the test result I will reply at next reply

  • 0 in reply to Mark Luo
    Prodigy 20 points

    but when battery nearly full charged, the charge current will below 50mA, and VBAT will not stable, and the charging state switches frequently;

    detail:  switch cv charging to charging done again and again

  • +1 in reply to Mark Luo
    TI__Genius 13905 points

    Hi Mark,

    Mark Luo said:
    VBAT measure result as follows.

    This waveform is typical of a floating VBAT point. It indicates the repeated charging and discharging for the battery capacitor while a battery is not present to stabilize the voltage. The Battery Capacitor will charge up to VREG, terminate, then begin to discharge until it hits the recharge threshold. At that point it starts charging again and the cycle repeats.

    Mark Luo said:
    VBAT will not stable

    This is a pretty significant difference in voltage (275 mV). I believe that the high voltage at the pulse is the voltage of VBAT in regulation and the low pulse is the actual battery voltage. While charging the VBAT pin will be higher than actual battery voltage by (Charge Current x Resistance to Battery) cell. If this difference is particularly large close to termination that means that the VBAT pin will fall below recharge threshold once charging stops.

    Can you try reducing termination current or lowering resistance from BAT to the battery cell? If the current is allowed to fall to lower value it will result in a smaller difference between VREG and the battery cell.

    Can you also confirm the voltage at the actual battery cell when the device is in this oscillating state? If it is the same as the lower voltage level this may help confirm that is the behavior we are seeing.

    Best Regards,

    Juan Ospina

  • +1 in reply to Juan Ospina
    Prodigy 20 points

    Thank you very much, you are right. Maybe our battery voltage drop too much  when disconnect BATFET, because of the battery behavior and I don't want to decrease charge current, So I disable ITERM, I let charge battery always, and let battery terminate charging itself.