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BQ27GDK000EVM: Calibration of Charge/Discharge Current

Steven Takata
Prodigy 180 points

Part Number: BQ27GDK000EVM

I am attempting to follow the instructions in sluu904A for the bq32z100EVM and slua334b for preparing optimized flash constants. I am using the GDK to charge and discharge my batteries but the current reported through the GDK interface does not match the current reported by the gas gauge.

I was able to successfully calibrate the bq32z100EVM after following the instructions here () and downloading the new BQStudio. 

I set a discharge current of 1250 mA and the gas gauge reports a ~750mA discharge. If I connect a DMM in series with the GDK, the same 1200 mA target discharge only reports ~250 mA by the gas gauge and matches with the DMM.

What can I do to either calibrate the GDK or increase the accuracy of the charge and discharge currents?

  • 0
    TI__Genius 14985 points
    Hi Steven,
    First, by bq32z100EVM do you actually mean the bq34z100EVM? I do not believe the bq27GDK000EVM is intended to work with bq34z100EVM so I'm curious how you got the GUI to display the GDK controls while connected to a bq34z100EVM.

    Do you mean that the actual discharge current drawn by the GDK reduced from 750mA to 250mA when you inserted a DMM in series, even though the GDK was configured to draw 1250mA of current?
    I would not expect an ammeter to impact the actual current drawn so something sounds odd.
    Nonetheless, this is rather an extreme error you are seeing. The GDK current is not required to be ultra-precise, since the accuracy of the gauge-reported current is more important.
  • 0 in reply to dMax
    Prodigy 180 points

    I did mean the bq34z100EVM as the gas gauge dev board I am using.

    From what I've read and according to the GDK user's guide, the EV2400 half of the GDK will happily pass signals from the connected EVM to the host PC.

    Yes, the output current was reduced by that much when my Fluke 287 was connected in series with the GDK.

    Here is a screenshot of the two disagreeing. This is without a meter in series.  When I did have the meter connected and during calibration the gauge matched the actual current quite closely.

    The GDK measures 1194 mA of a 1250 mA set point and the gauge measures 780 mA.

    Are J4 and J8 the correct place on the GDK to connect to Batt+ and Pack- respectively on the bq34z100EVM?

    How can I check the firmware version on the GDK microcontroller? (The EV2400 portion firmware is at the current 0.18 level). What is the current GDK firmware version?

  • 0 in reply to Steven Takata
    TI__Genius 14985 points

    Hi Steven,
    Can you please attach a picture showing all of your connections and setup? We just did a quick test and could get the gauge and GDK to report similar currents, although it did require calibrating the bq34z100EVM current.

  • 0 in reply to dMax
    Prodigy 180 points

    Here are photos of my setup.

    J4 on the GDK is connected to BATT+ on the EVM.

    J8 on the GDK is connected to PACK- on the EVM.

  • 0 in reply to Steven Takata
    TI__Genius 14985 points
    Hi Steven,
    Your connections appear correct.
    Is the molex connector between your battery and the bq34z100EVM using soldered connections or just inserted pins? The connection may not be so good if they are just inserted.
    Perhaps your ammeter is limiting the current or somehow influencing the measurement.
  • 0 in reply to dMax
    TI__Genius 14985 points
    Hi Steven,
    Have you resolved your issue?