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BQ21061EVM: Charging is not stopping at VBATREG.

Jainam Shah
Prodigy 50 points
Part Number: BQ21061EVM

Hello,

I am using this module to charge the 3.8V 385mAh battery. I have set the VBATREG at 4.35V. But the charger doesn't reduce the current at 4.35V. It continue charging till 4.5 V. 

I have setup the register as below. 

VBAT_CTRL = 0x4B  ( VBATREG = 4.35V)

ICHG_CTRL  = 0x9A  (ICHG = 192.5)

TERM_CTRL = 0x2A (21% of ICHG)

All other registers have the default values. After reading in datasheet I found that I have set the PMID voltage to 4.5V. And the recommended value is 200mV higher then the VBATREG. but by I2C I can only set it to 4.4V. Is there any hardware setting I can do to set the PMID to 4.37V. 

And Please let me know if is there any other changes require to fulfil the charging condition. 

Thank you. 

  • 0
    TI__Genius 13565 points

    Hi,

    This is unexpected behavior, as the battery voltage approaches VBATREG the charge current should reduce and approach zero. As it approaches 0 and falls below termination then charging should cease. For this to occur at 4.35V then the VBAT_CTRL register should be set to the 0x4B like necessary and PMID should be regulated at least 200mV above battery. Having PMID regulate to 4.4V should actually cause the device to enter DPPM as battery voltage increases, thus reducing charge current before it gets to VBATREG and not allow the device to reach termination. Despite not reaching termination, the battery should not charge above about 4.25V (charge current should reduce to 0, though technically not terminated).

    For a VBATREG of 4.35V, PMID should be set to regulate to at least 4.55V (4.6V being the closest available setting). Are you able to set it to 4.6 in I2C?

    What is the charge current when battery voltage is 4.35V and 4.5V? 

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 50 points

    Hi,

    For both Voltage level 4.35V and 4.5V charge current was 192mA. I have manually stopped charging as charge current was not reducing at any voltage level.

  • 0 in reply to Jainam Shah
    TI__Genius 13565 points

    Hi,

    This is very unexpected, it seems to indicate that the charger is not entering the constant voltage stage portion of the charge cycle. It also does not seem to indicate that VDPPM Status is active as would be expected if VBAT was 4.5V but PMID was regulating to 4.4V. Can you please provide the register values when BAT is 4.35V and also 4.5V?

    Additionally, can you please provide a waveforms of VBAT, IBAT, VIN, and VPMID at these two battery voltages as well?

    Best Regards,

    Juan Ospina