Other Parts Discussed in Thread: BQSTUDIO, , EV2400, BQ27220, BQ35100
Hi,
We are currently doing a design using 2 primary batteries in series and we plan to use the bq34110 as a Coulomb Counter. Right now, I am looking at all the documentation and the I2C interface with the device seems simple enough. Where I'm having some issues is with 1) the TI tool "Gauging Parameter Calculator for CEDV gauges" (GPC), 2) the calibration procedure, and 3) some general use of the device.
1) GPC tool
1.1) We have ordered the bq34110 eval board BQ34110EVM-796 as well as the I2C interface adapter EV2400. What I was planning to do was create our own CEDV profile with the GPC tool, as there is no profile for our batteries in bqStudio. As such, there is no ChemId as well. Can I use the GPC tool with the wrong chemId? Can I use the GPC tool at all with primary batteries?
1.2) The GPC guide sluub45a says that 2 tests (at 2 different continuous discharge rates) should be performed at 3 different temperatures. As our product will only be used at room temperature, is it still mandatory to have a profile for 3 temperatures?
2) Calibration procedure
2.1) There is no document aimed precisely at the calibration procedure for the bq34110, so I've read here and there some application notes for other fuel gauges. What I understand is that the Board Offset calibration should be done on the PCB that will have the bq34110. However, in the bq27220 calibration guide (slua771), it says to "Ensure no current is flowing through the sense resistor during these steps". How should I proceed with that, as the microcontroller will necessarily have to run, along with the bq34110 and some other circuitry?
2.2) In the bq34110 Technical Reference Manual (sluubf7), at section 5.10 - Current Calibration, it talks about the CC Gain and CC Delta. I read on another thread that those parameters are used to translate the Rsense on the PCB. My first thoughts would be that this calibration can be done with the eval board and bqStudio, but that I should unsolder the 10 mOhms and put a 20 mOhms (what we want to use) for the calibration data to be correct, is that right?
2.3) Since we won't need an external voltage divider (VBAT_max will be ~3V), can the Voltage Calibration Procedure be omitted?
2.4) As I said, our product will mainly be used at room temperature. As we plan to use the internal temperature sensor of the device, can the Temperature Calibration be omitted?
3) General use
3.1) I calculated the LSB value of the CC ADC to be ~760 uA (Minimum readable current = (SRP_max - SRN_min) / Rsense / n_steps = (0.125 - (-0.125)) / 0.02 / (2^14 - 1) = 762.986 uA). However, our application will sometimes only have the bq34110 running as well as a crystal (rest of the circuit won't be powered), which will result in a current consumption under the minimum readable current. Can I use the AccumulatedTime() function to approximate manually the energy that was consumed during a time-off of the system? Is this timer active even if the bq34110 does not detect any current?
3.2) As this design will use primary batteries, the batteries will have to be changed sporadically. Will we need to somehow reset the coulomb counter, or will a good CEDV profile (with the GPC tool) help detect the "new" condition of the batteries?
Thank you for your time,
Fred
