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bq34z100 some basic getting started questions

Joe Perino
Intellectual 640 points
Other Parts Discussed in Thread: BQ34Z100, BQEVSW

Hello,

 

We are looking at using the bq34z100 fuel gauge in a high-capacity 16s design.  I have some basic questions to clarify some issues with regards to configuring the flash, and working with the evaluation board.

Is it possible to modify the evaluation board to work with a 64V battery?

The capacity of the battery is 30Ah.  For a nominal 50V this makes the design energy 1,500,000 mWh.  I need some clarification on the x10 mode and the design energy scale factor.  The battery will be operated in CC mode.

If we select x10 mode, then is it true that EVERY setting in the flash for which the units are mAh should be scaled by a factor of 10?  And in conjunction with doing that, the current calibration should be "fooled" by, say, entering 200mA when a 2A load is applied for the current calibration?

Then, if the design energy scale factor is set to 10, does that mean that the design energy is really scaled by 100 because current is already scaled by 10?  Since the value for the register can be any number between 0-255, can I use a larger energy scale factor if necessary?  Otherwise, I cannot enter a value large enough for our design.  And does all of that really matter if we are using a constant-current load model?

 

Thanks,

Joe Perino

Nova Battery Systems

 

  • 0
    TI__Expert 6470 points

    Hi Joe,

    1. Yes, just follow the formula for divider resister calculation in the datasheet and solder the resistor onto the test pins of the EVM. When you get up near the 65.5V limit, the resistor value may become a bit critical. The "trick" is to find the value that always lets you calibrate it by having a calibration factor under 65536. Why? because the register in the gauge is only 16 bits wide.

    2. Forget about power and energy in this case. Use Load Mode=0 for constant current. Then, set all parameters with units of mW or mWh to zero.

    3. The x10 "mode" does nothing but remind the host to scale it. You can use any scale factor you like. In this case, unless the max current is over 32.7A, you can use the defaults and not do any scaling. If you have currents above 32.7A, then you should scale accordingly, maybe 2X. This involves cutting all mA and mAh settings in half and calibrating with twice the current that you specify in the calibration screen. Then, the host has to know that the reported current and mAh are really twice what is read.

    Regards,

    Doug

  • 0 in reply to Joe Perino
    Intellectual 640 points

    We have designed a very high capacity pack around the 34z100.  The design uses a very low value of sense resistance (1.5mOhm).  We built up a prototype board, and find that when configuring the data flash, CC GAIN will accept a 1.5mOhm sense resistance, but CC DELTA will not accept a value below 4.759mOhm.  Can we use a <5mOhm sense resistor for our high-current application with this device?  What issues/problems may arise with the calibration because of the CC Delta limitation?

    Thanks,

    Joe Perino

    Nova Battery Systems

  • 0 in reply to Joe Perino
    TI__Guru 73830 points

    Joseph,

    You can use a smaller sense resistor. If the bqEVSW is limiting your entry selection, then you can export a gg file, change the parameter and import it back into the device.


    Regards

    Tom