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BQ34Z100-G1 minimum shunt resistance

Svetoslav Pirev
Prodigy 155 points
Other Parts Discussed in Thread: BQ34Z100-G1, BQSTUDIO

Hello everyone,

I would like to ask how much could be the minimum BQ34Z100-G1 shunt resistance  ?

BQ34Z100-G1 datasheet says:

8.3.5 Fuel Gauging

....

The bq34z100-G1 monitors charge and discharge activity by sensing the voltage across a small-value resistor (5 mΩ to 20 mΩ typ.) between the SRP and SRN pins and in-series with the cell. By integrating charge passing through the battery, the cell’s SOC is adjusted
during battery charge or discharge..


I have an automotive design where shunt resistance is 100 microohms and battery capacity is 100 Ah (lead-acid battery).

Could I use BQ34Z100-G1 for this application ?

Thank you

  • 0
    TI__Guru 73830 points

    You can use a smaller sense resistor, but note that the input offset is about 10uV so the current detection at lower current levels will be limited.

  • 0 in reply to ThomasCosby
    Prodigy 155 points
    Thank you Tom,

    I didn't touch the design a long time and today I'm trying to program bq34z100-g1 with CC Gain = 100microohms, CC Delta = 100microohms but unfortunately bqStudio don't want to accept these values. The status message is: Value is beyond maximum value defined for parameter.
    Does some one know how to enter 0.0001 ohms into these fields ??

    Thank you
  • 0 in reply to Svetoslav Pirev
    Prodigy 155 points
    Another question arrive, if I'm using 12V Pb AGM battery with 100 Ah capacity and Design Scale of 4 then
    Design Capacity = 25,000 mAh
    Design Energy = 25,000 mAh * 12V = 300,000 mWh
    Design Scale = 4

    But Design Energy field min/max is from 0 to 32767 mWh. How to scale to fit in this range ??

    I'm trying to program different chemistry and I'm expecting that after the programming
    Design Capacity and Design Energy should be changed but they are not. BQ34Z100-G1 keep
    my old programming values. For an example, chemistry ID 0x0803 is Enersys Cyclone_D
    2500 mA/h battery, after programming Design Capacity should be 2500 mA/h, am I right ??
  • 0 in reply to Svetoslav Pirev
    TI__Guru 73830 points

    All parameters in the device are based on the cell level, so the Design Energy will be 25000mA x 2V = 50000mA. You will need to use a higher Design Scale to bring it under the 32767 limit.


    The ChemID does not contain capacity information. These will be calculated when you run the optimization cycle.

  • 0 in reply to ThomasCosby
    Prodigy 155 points

    Thank you Tom.

    I would like to share how I resolve the problem with CC Gain and CC Delta. According to BQ34Z100-G1 data sheet CC Gain could be from 0.1mOhms to 40mOhms.  The smaller value that I could enter in bqStudio's CC Gain field is 0.125mOhms. If I try 0.1mOhms bqStudio doesn't accept it. What I did is to use the bqStudio's Calibration Window, I ran discharge current of about 20A then I calibrated the gauge saying that current is -20,000mA, switch back to Data window and read what the gauge wrote in CC Gain. If it is higher than 0.1mOhms, then switch back to Calibration Window and enter a smaller current, let say -19,000mA, calibrate again and read back CC Gain from Data window until the gauge write 0.1mOhms.  During the calibration BQ34Z100-G1 properly adjust CC Delta field.

    Then I created a GoldenImage file.

  • 0 in reply to Svetoslav Pirev
    TI__Guru 73830 points
    Svetoslav,
    Thank you for the hint.
    Tom