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BQ25700A: BATDRV behavior in BATOVP

Tamio Yokokura
Expert 3560 points
Part Number: BQ25700A

Hi, Charger support team

My customer changes REG0x15:MaxChargeVoltage to 8400mV from 8800mV when Gas Gauge in battery pack detected the full charge condition.

Of course, REG0x14:ChargeCurrent is changed to 0mA.

According to the datasheet of BQ25700A, battery pack is discharged with 20mA via SRP pin and SRN pin when BATOVP is detected.

Other operation is not explained.

My customer say that BATDRV seems to oscillate when the system current is flowed in BATOVP.

Have you heard the phenomenon like this?

Regards,

Tamio

.

  • 0
    TI__Guru 56650 points
    First, if VBAT is 8400mV and ChargeVoltage register value is 8800mV, we should not see the BATOVP.
    When the input source is available, the BATFET operates at ideal diode mode. If a load transient makes the VSYS below VBAT, it could make BATDRV on. Please check VSYS and VBAT.
  • 0 in reply to Wang5577
    TI__Expert 3560 points

    Hi, Wang,

    I duplicated the same abnormal oscillation of BATDRV as our customer using BQ25700A/10 EVM.

    The below is waveform.

    The condition when I duplicated is as follows;

    • Charge Voltage=8000mV
    • Charge Current=0mA
    • Battery Voltage=8.8V to 7.5V step=10mV, by Vi-polar Power Supply
    • System Current=3A to 0A, Freq=3kHz, Duty=20%, SlewRate=2.5A/usec, by Electronic Load

                                  

    You can also duplicate using EVM under the condition.

    • CELL_BATPRESZ configuration=2-cells : JP2=SHORT, JP3/JP4=OPEN
    • VBAT=8800mV
    • VIN=20V/3.0A
    • ChargeVoltage=Default (8400mV) at POR
    • ChargeCurrent=Default (0mA) at POR

    If you can't see the abnormal oscillation of BATDRV, please change VBAT voltage to the upper.

    The charge voltage of battery pack which our customer uses is 8800mV.

    When the adapter is removed and inserted after the battery pack was fully charged, the abnormal oscillation occurr.

    If the adapter is connected to PC system via the docking station, the PD controller detects the over current due to the abnormal oscillation and the power switch is turned off.

    As the result, PC system is blinked the display monitor.

    As far as the battery pack of the high charge voltage is used, there are possibility to cause the same issue at all customer.

    Please confirm this phenomenon using your EVM, and explain the reason why the abnormal oscillation occurred.

    Regards,

    Tamio

  • 0 in reply to Tamio Yokokura
    TI__Guru 56650 points
    For a normal application, the charge voltage register value should be higher than the battery voltage.
    In here, the battery voltage could be higher than VSYS regulation voltage. The BATFET has an idea diode operation: if VBAT>VSYS even with a small voltage number, the BATFET would be turned on. What is the interval timing for 10mV/step?
  • 0 in reply to Wang5577
    TI__Expert 3560 points
    Wang,

    I am sorry to respond so late.
    Firstly, the interval time is 15msec. But the abnormal oscillation is not affected by the interval time.

    The charging voltage of their application is higher than battery voltage, too.
    But, EC set REG0x15(ChargeVoltage) to 0mV when the gas gauge IC in battery pack is set to FC=1.
    As the result, the charge voltage is set to 8400mv. The abnormal oscillation was observed.
    Basically, I think that this is the system issue. I suggest that EC never set REG0x15 to 0mV or 8400mV when the FullCharge was detected.
    Perhaps, this issue will be fixed by changing EC.

    Thanks,
    Tamio
  • 0 in reply to Tamio Yokokura
    TI__Guru 56650 points
    Tamio,

    Thank you for detail explanation. I agree "this is the system issue. I suggest that EC never set REG0x15 to 0mV or 8400mV when the FullCharge was detected."