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BQ34Z100-R2: Voltage and temperature calibration issues

Part Number: BQ34Z100-R2
Other Parts Discussed in Thread: BQ76952, BQSTUDIO

Tool/software:

Hi,

I'm working on a project that involves the BQ34Z100-R2 and I have run into an issue while calibrating the voltage and the external temperature.

Voltage:

I'm supplying 50V through a power supply and following the steps outlined in Texas Instruments' 'Voltage Calibration' video on YouTube.

However, after entering the correct applied voltage and running the calibration, the voltage reading shows 65535V, which is incorrect.

Also, the Voltage Divider value is updated as follows: (default was 5000)

For your information, the following snapshot shows our Pack Configuration setup and we are using 15-cell battery pack. Also, I have programmed the ChemID that matches our cell.

Temperature:

As you can see in the image above, the bit[0] of the Pack Configuration is set to 1 to specify external temperature source. Also, an external temp sensor is connected to TS pin and I'm calibrating the temperature as follows:

And the following shows the calibration result, which is not the value entered into the "Applied Temperature" field.

What am I doing wrong here to get the voltage and temperature calibrated?

Thank you,

Kyungjae Lee

  • Hi,

    Can anyone help me get through this point please?

    Thank you,

    Kyungjae Lee

  • Hi Kyungjae Lee,

    Voltage:

    Can you lower the voltage on your power supply to 5V, use the internal voltage divider, set voltage divider to default, and number of cells in series to 1.

    Then try to calibrate the device, the gauge should then report voltage correctly.

    Temperature:

    What type of thermistor are you using?

    Does the connection follow the same scheme on the EVM?

    Regards,

    Diego

  • Hi Diego,

    Thank you for the guide.

    As for the voltage, unfortunately, I wasn't able to follow your guide as the Fuel Gauge on our custom board is powered up by an AFE(BQ76952) which shuts down before the applied voltage reaches 5V.

    According to the EVM documentation, it looks like 5V is the maximum allowed voltage for the single cell mode and I can't achieve this with our custom board design at the moment.

    Would there be any other way to successfully calibrate the voltage?

    As for the temperature, I'll get back to you when I have the answer for your question.

    Thank you very much!

    Kyungjae Lee

  • Hi Kyungjae,

    Ok not a problem, let's try this, use the external voltage divider and configure it correctly so that it is XXXXmV:1000mV ratio. Then apply a voltage that satisfies the AFE and calibrate the gauge using the power supply. The gauge should then read the correct voltage. 

    Then update the number of cells in series to the correct number and divide your voltage divider parameter by the number of cells in series. Your gauge should then again read the correct voltage.

    Regards,

    Diego

  • Hi Diego,

    Thanks again! I thinking I'm making some progress but the end result is not quite accurate.

    Here's the steps I followed:

    1. Set the applied voltage (power supply) to 45V

    2. Use the external voltage divider (set the PackConfiguration[VOLSEL] bit)

    3. Use the voltage divider 45000

    4. Calibrate the gauge using the power supply -> The gauge read correct voltage, 45000mV

    5. Update the number of cells in series to 15 -> The gauge reading changes to 65535mV

    6. Changed the voltage divider to 3000 (i.e., 45000/15) -> The gauge reading changed to 34620mV

    Unfortunately, this is not the applied voltage 45000mV.

    Is there any other factors that I need to consider to achieve the correct calibration?

    Thank you,

    Kyungjae Lee

  • Hi Kyungjae,

    Your process looks correct,

    What are your resistor values for your voltage divider?

    45000, corresponds to a 45000mV to 1000mV ratio

    is any voltage scaling being done?

    Regards,

    Diego

  • Hi Diego,

    No there is no voltage scaling being done (Volt Scale = 1), and the resistor values of our voltage divider are 1M Ohm and 17.4K Ohm. For your reference, the nominal voltage of our battery pack is 53V.

    Hope this helps!

    Thank you,

    Kyungjae Lee

  • Hi Kyungjae Lee,

    Thanks for clarifying, the value you should enter into BQstudio is 58471mV.

    Please use this in step 3 of your process above and see if this corrects the error.

    Regards,

    Diego

  • Hi Diego,

    It did the trick.

    I went back to step 3, entered 58471 into the Voltage Divider field, ran the calibration, changed the number of cells in series to 15, updated the Voltage Divider value to 58471/15, and then the battery voltage changed to 44970mV, which is pretty close to the applied voltage 45000mV.

    What was the logic behind choosing the value 58471? I thought I could start from any value that satisfies the XXXXmV:1000mV ratio.

    Thank you,

    Kyungjae Lee

  • Hi Kyungjae Lee,

    using this equation, and solve for Vs

    Vout = Vs*R2 / (R1+R2) 

    1V = Vs *17.4K/(1M+17.4K)

    Vs = 58.471V

    Therefor your voltage divider is 58.471 to 1V.

    58471mV as the voltage divider parameter.

    Hope that makes sense!

    the website you used can do this for you!

    Regards,

    Diego

  • Hi Diego,

    Thanks for the explanation, that resolves my question about the voltage calibration!

    As for the questions you asked earlier about our external thermistors, the type of thermistor we are using is NTC thermistors and the following snapshot shows how our thermistor connector is connected to the device:

    as compared to the EVM scheme

    would this be sufficient to further our discussion?

    Thank you,

    Kyungjae Lee

  • Hi Kyungjae Lee,

    What type of thermistor are you using? It should be the Semitec 103AT thermistor, this is what the default thermistor coefficients are set up for.

    Have you calibrated temperature?

    Do you have the gauge registers configured for external thermistor use?

    Regards,

    Diego

  • Hi Diego,

    My apology for the delayed response.

    Yes, I did try calibrating the temperature, but the calibration result was not quite right as I shared in our earlier conversation. And yes I did configure the register to use external thermistor.

    The thermistors we are using is not exactly the Semitec 103AT, but they seem to have similar specs. The following is the spec of the thermistors we are using:

    • R24 = 10Kohm ± 1%
    • B25/50 = 3950K ± 1%
    • B25/85 = 3977K ± 1%

    The only difference I found between them was the B value. Would you regard this as a potential cause?

    I lifted the following from the datasheet of the Semitec 103AT.

    Thank you,

    Kyungjae Lee

  • We are currently looking into this, we will get back to you soon.

    Regards,

    Adrian

  • Thank you Adrian,

    I also wanted to ask if the following thermistor would be compatible:

    103AT-5-1P

    Thank you,

    Kyungjae Lee

  • Hi Kyungjae Lee,

    Can you share your thermistor part number.

    Can you also share your .srec.

    Regards,

    Diego

  • Hi Diego,

    The part number is MT-9S103FD1365T-0290. And, I'm new to .srec file format. Could you be a little more specific?

    Thank you,

    Kyungjae Lee

  • Hello Kyungjae,

    That thermistor looks fine for this gauge. The srec file can be pulled from the gauge using the "Golden Image" tab in BQStudio.

    Regards,

    Adrian

  • Hi Adrian,

    Please find the .srec file in the link below:

    https://drive.google.com/file/d/19rueFU0Em1ogtvl3ZsT1bH9b0G92Zxwz/view?usp=sharing

    Also, the bqStudio doesn't seem to have "bq34z100-r2" device registered. Can you please add this device to the supported device list if it matters?

    Thank you,

    Kyungjae Lee

  • Hi Kyungjae Lee,

    Thanks for the .srec, please allow me some time to look into this.

    100_2_02 refers to BQ34z100-R2.

    Regards,

    Diego

  • Hi Kyungjae Lee,

    I was able to calibrate your gauge using the calibration tab in BQstudio.

    Were you ever able to get this thermistor calibrated?

    Regards,

    Diego

  • Hi Diego,

    I appreciate your patience. It turns out that the root cause was on our hardware design around the thermistor connection. I was able to workaround it and get the temperature calibrated.

    So I would say, problem resolved.

    Thanks for your support!

    Best regards,

    Kyungjae Lee