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Original question:

BQ27220: FCC_LIMIT bit register address

BQ27220: Qualified discharge?

Vignesh Rajagopal
Prodigy 240 points
Part Number: BQ27220
Other Parts Discussed in Thread: BQSTUDIO, EV2400

Hi all,

Debugging the BQ27220 fuel gauge on our product and I ran a quick test to try and capture charge/discharge cycles. I ran an overnight test with the device discharging and monitoring the VDQ bit, per this snippet from the reference manual:

When I came back to the setup this morning, I found through the UART logs that the VDQ bit had not been set. The battery had hit 0% and shutdown, but VDQ remained at 0 the whole time. The only bit I saw change in the OperationStatus() register was the EDV2 bit, which should get set when below the EDV2 voltage threshold, i.e. 3.501. Note however that based on my logs, this bit actually got set at around 3.616V based on the fuel gauge's voltage reading.

When does a qualified discharge begin?

Thanks,

Vignesh

  • 0
    TI__Guru** 105760 points

    Hello Vignesh,

    Can you share the log file here so we can review it? Can you also export your .gg file so we can look at your settings?

    I believe there was an issue with the photo upload as well.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 240 points

    Hi Wyatt,

    Thank you for your response. The photo was just a screenshot from the reference manual; I have attached it here for reference. 

    Is there a way to securely share the log file with you in order to avoid posting it on a public forum? The log file is from our processor, and it simply polls different characteristics from the fuel gauge every 5s.

    I'm not sure what the .gg file is or how to export it. From my understanding, it's only something that can be generated from the EVK, but I may be mistaken. Please advise on how I can provide this file to you.

    Thanks,

    Vignesh

  • 0 in reply to Vignesh Rajagopal
    TI__Guru** 105760 points

    Hello Vignesh,

    You can friend me on E2E and send them over private message.

    The .gg file you can pull using the EV2400 and bqStudio, you will need to connect the communication lines to the EV2400 but you don't need a EVM.

    If you have done a full cycle the VDQ should be set when you start to discharge, did you do a full charge before discharging?

    The condition for DCR are explained in the TRM:

    Discharge Count Register (DCR) —

    The DCR counts up during discharge, independent of RM. The DCR counts discharge activity, battery load estimation, and self-discharge increment. The bq27220 device initializes the DCR at the beginning of a discharge to FCC – RM when RM is within the programmed value in Near Full. The DCR initial value of FCC – RM is reduced by FCC/128 if [SC] = 1 in CEDV Gauging Configuration and is not reduced if [SC] = 0. The DCR stops counting when the battery voltage reaches the EDV2 threshold on discharge.

    You may need to adjust your Near Full value to get a valid discharge.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 240 points

    Thanks Wyatt. I'll be sending over the logs now.

    If I'm understanding correctly, we would need to connect the I2C clk/data lines of our device to the EV2400, correct? And then we would be able to pull the .gg file? I'll have to check whether this is feasible from a hardware/rework perspective; is there any other way to obtain this file, perhaps over I2C from the processor?

    Yes, I did do a full cycle charge before starting to discharge. We have already set our Near Full value to 40mAh for our 600mAh battery. What other values are relevant for the BQ27220 to detect a valid full charge?

    Thanks,

    Vignesh

  • 0 in reply to Vignesh Rajagopal
    TI__Mastermind 24870 points

    Hello Vignseh,

    Yes. The EVM user's guide also describes this process.

    You will need to refer to the primary charge termination conditions in the TRM for valid full charge.