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How to successfully calibrate Pack Voltage?

SW5307
Intellectual 825 points
Other Parts Discussed in Thread: BQEVSW, BQ76PL102, BQWIZARD, BQ78PL116

The purpose of Pack Voltage Calibration is to calibrate a gain factor, the DF:AFE_Pack_Gain, if the gas gauge is to read more accurately the voltage from PACK pin. AFE Pack Gain may not need to be calibrated depending on the application.  Unless Pack Voltage is used for display by the application then it will only be used for charger detection and it does not need to be accurate for function. The default DF:AFE_Pack_Gain of 672.91 uV/cnt is a good value for most cases.

 

However, if customers do need to calibrate Pack Voltage, In bq20zxx family bqEVSW, there is a button in the "calibration" screen for "Pack Voltage Calibration". Unfortunately, it does not offer a clear procedure to ensure a successful Pack Voltage calibration. After clicking on the button, it prompts:

 

"FETs will be turned on!  The voltage calibrated in Voltage Calibration will be used. Press Cancel if Voltage Calibration has not been performed on this pack."

 

Customer may see various problems if just following the above prompt: in accurate pack voltage reading even after the calibration, or even negative AFE_Pack_Gain (if the battery voltage is low)!!

 

What is missing here is that the user must set DF:Voltage_Signal (in the Calibration subclass) to the actual battery stack voltage before proceeding to do Pack Voltage Calibration.

 

We are working to fix this problem in future bqEVSW release.

  • 0
    Prodigy 140 points

    Hello，SW

    Sorry to bother you.I have some problems when I use bq78pl114EVM in voltage calibration.And I use 4-cells. According to User‘s Guide,I  calibrate voltage .I have updated the firmware to 5000 and began to calibrate voltage.But the voltage reading is 4200mV ,and the actual voltage of Lithium battery is about 3800mV.There are differences between them ,I dont konw why.Bsides, I also use firmware 4452 to calibrate voltage ,and each of the voltage reading is about 3700mV,it is smaller than the actual voltage,and the error between them is too big(about 70mV each cells ) .So would you analysis the reason of this ?

    Thanks

    Randy

  • 0 in reply to yuxiao gong
    Prodigy 170 points
    I'm working with a board equipped with BQ78PL116 and BQ76PL102 in a 10S4P configuration. I replaced the BQ78PL116 as a result of damage. However, in the replacing it was not be possible to solder the central thermal pad. I have tried all the functionality of the BMS, and goes correctly. But, in the cell's voltage measurement there is a mismatch of about 200mV between the values of bqWizard and Multimeter/Oscilloscope only at the cells V1 and V2 . All the others bqWizard's voltage reading (V2..V8) are perfectly matching the values of the Multimeter. Is it possible that this problem is caused from the BQ78PL116's thermal pad left unsoldered, and so without a fixed reference voltage? Does the [V1,V2] ADC voltage converters has some ground reference attached to the thermal pad?