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BQ25895: Status Register REG0B never changes

Andrew Wode
Prodigy 30 points
Part Number: BQ25895
Other Parts Discussed in Thread: BQSTUDIO, EV2400

Tool/software:

Regardless of whether a battery is connected or not, the status register always returns 0xB6.

Also curiously, when the battery is not connected, the Battery Voltage reads 4.20V.

Any hints on where to look next?

Thanks in advance!

  • 0
    TI__Guru** 105870 points

    Hello Andrew,

    Are you reading with the EV2400 and BQStudio? Are you testing with our EVM or a custom PCB?

    If you have an adapter connected and no battery, the status reported and battery voltage seem to be correct, the charger will keep retrying each time the BAT voltage drops, small amount of charge will be in the capacitance on BAT.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 30 points

    Hi Wyatt, thanks for your response. 

    I'm reading the registers with I2C on a custom PCB. Of course, I'm using serial to print the register values and the USB cable provides both comms and power. So this, combined with your answer, seems to explain it.

    I just want to confirm though, that you're saying that "Fast Charging", 10 on [4:5] is correct? I would have expected Not Charging, 00. 

    Similarly, throughout the charge cycle, regardless of initial and termination battery voltage, the register never changes to e.g., 11 (Charge Termination Done).

    Have I misunderstood something here?

  • 0 in reply to Andrew Wode
    TI__Guru** 105870 points

    Hello Andrew,

    STAT should be pulsing and the register should be changing between not charging, charge terminated, and fast charging.

    Have you confirmed VBAT with a oscilloscope to see if it's truly 4.2V? Many times it is related to the I2C driver not reading the data correctly as well.

    Sincerely,

    Wyatt Keller