Tool/software:
Hi all,
In our application we've used the BQ35100 as the Fuel Gauge in a accumulator mode. When our application is actively measuring, we're making a total of three measurements at different intervals. The most significant energy cost is between the first and the second measurement. During validation of BQ's reported charge consumption we've noticed that the Fuel Guage reports about 105 µAh below our reference measurement. This is consistent even when the charges measured differen in peak-to-peak distance, the time taken, and the overall charge consumed. We're sampling AccumulatedCapacity to determine how much energy has been used.
To provide some more context about the configuration of the Fuel Gauge in our application:
- Calibration has been performed and reported current measurements match with our reference measurement.
- Board Offset, CC Offset, vOffset, ccGain, ccDelta (see chapter 3 of SLUUBH1C) have all been calibrated.
- The measured Voltage is in line with our reference measurement.
For the measuring set-up, the following applies:
- Our reference measurement device samples with as close the same frequency as the BQ35100 (50 kHz for our reference measurement device, about 65 kHz for the BQ35100 according to support forum posts).
- The time-stamps of when we sample the Fuel Gauge are matched with the reference measurements to ensure the same charge is measured.
- The reference measurement device has better accuracy when compared to our Fuel Gauge application (0.5 nA resulution for the reference device compared to 137 µA for the Fuel Gauge set-up).
- The charge we want to measure is always above 100 mA.
The data we want to measure, has the following properties:
- Duration varying between 4 to 8 seconds.
- Peaks which very briefly can exceed our measurement range (less than 100 ms).
As mentioned, the issue we've got is that the the Fuel Gauge consistenly reports about 105 µAh less charge consumed than our reference device measures. This negative offset is regardless of duration, peaks, or total charge. It's an absolute value instead of being relative. We'd like to hear suggestions from the community about where we can look for this strange offset.
