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BQ27426: How can I input the battery temperature into the FuelGauge by means of an external input?

Wang Dong
Intellectual 600 points
Part Number: BQ27426

Hello.

The BIN pin of our device FuelGauge is grounded.

The battery temperature needs to be input externally via I2C and OpConfig[TEMPS] is configured to 10b, is this the right operation?

Is it correct to write the temperature (Celsius converted to 0.1k) via Temperature() after configuring to 10b?

The current phenomenon: OpConfig [TEMPS] is configured to b10 and the cycle writes the K value of the battery temperature, FCC, RM and SOC are all 0

How can I input the battery temperature into FuelGauge by means of external input?

  • 0
    TI__Guru 57697 points

    Hello Wang,

    The procedure you described is correct. You can read the temperature back to verify if the gauge accepted it or not.

    However there are other requirements that need to be met. See datasheet for more information. Here is a snippet for quick reference.

  • 0 in reply to Shirish
    Intellectual 600 points

    Thank you for your support.

    After the temperature is written, the readback is executed, and the temperature written is the same, so there is no problem with the write temperature operation. (The original question has a sticker chart)

    The BIN pin on the device is connected to GND, also add 10K resistor.

    What other reasons would cause RM, FCC, SOC to become 0 after the temperature is written? Do I need to do some state judgment before writing temperature?

    Also after configuring OpConfig[TEMPS] to 10b, is the temperature the last value during the interval between two temperature writes?

  • 0 in reply to Wang Dong
    TI__Guru 61006 points

    The gauge will re-simulate a discharge if temperature changes by more than 5deg.C. If this temperature causes a significant increase in cell resistance (which is a function of temperature) and the load select is so that the gauge uses a significant discharge current, then the discharge simulation may calculate a loaded voltage that drops below Terminate Voltage immediately, thus causing 0mAh FCC and RM.

  • 0 in reply to Dominik Hartl11
    Intellectual 600 points

    Thank you for your support.

    After configuring OpConfig[TEMPS] to 10b：

    1. What is the default value of temperature if no temperature is written externally to Fuelgauge?

    2. At what point does the temperature have to be written, after the FS file is loaded successfully?

    3. What is the interval between temperature writes?

    4. After the temperature is written to fuelgauge, will the temperature value be saved? Before writing again, will the temperature value be the same as the previous value?

  • 0 in reply to Wang Dong
    TI__Guru 57697 points

    Hello Wang,

    The temperature value must be written as soon as possible after writing the FS file. There is no fixed interval for temperature writes. Until the next temperature value is written, the temperature will stay at the previous value.

  • 0 in reply to Shirish
    Intellectual 600 points

    Thank you for your support.

    Can you provide a flow chart or example code for temperature writing?

  • 0 in reply to Wang Dong
    Intellectual 600 points

    Hello Shirish，

    The external temperature can already be written to the FuelGauge.

    There are still the following questions that you need to help confirm.

    1、What is the effect of writing to readonly registers?

    2、What is the problem of writing multiple read-only registers (Fcc\Rm\Current\Voltage etc.) to FuelGauge IC according to 1Sec cycle?


    3、Will it cause Fcc\Rm\Soc to be 0 if FuelGauge IC is heavily loaded?

  • 0 in reply to Wang Dong
    TI__Guru 61006 points

    #1: There is no effect.

    #2: The gauge may experience a watchdog timer reset in some cases, if you exceed more than 2 standard commands per second.

    #3: This is unlikely.

  • 0 in reply to Dominik Hartl11
    Intellectual 600 points

    Thank you for your support.

    What is the specific scenario of #2?

  • +1 in reply to Wang Dong
    TI__Guru 61006 points

    If the gauge is busy (e.g. running a long discharge simulation), and the host uC issues commands frequently (which will interrupt the discharge simulation), the discharge simulation may run too long in total (simulation time + interruptions) and the watchdog timer can expire.

  • +1 in reply to Dominik Hartl11
    Intellectual 600 points

    Thank you for your support.

    Is there a description of this in TI's documentation? What are the corresponding documents and chapters?

    There is a description in the Technical Reference document as shown in the figure below, is there any other basis other than this?

  • 0 in reply to Wang Dong
    TI__Guru 61006 points

    It's in the TRM and also the datasheet: 

  • 0 in reply to Dominik Hartl11
    Intellectual 600 points

    Thanks for your reply！

  • 0 in reply to Shirish
    Intellectual 600 points

    There is one more question that I need you to answer.

    If OpConfig[TEMPS] =10b.

    1、What is the default temperature of fuelgauge before host writes temperature?

    2, host has not written the temperature to Fuelgauge, fuelgauge to get the temperature value to retain the default value? Or will it actively change to Fuelgauge's internal sensor?

  • 0 in reply to Wang Dong
    TI__Guru 61006 points

    #1: The default value is 20deg.C (before it takes a measurement)

    #2: The gauge will start measuring internal temperature so if you didn't change the configuration before it updated temperature (from 20deg.C default), then it will use what it measured on-chip.