BQ34Z651: BQ34z651 - Not Calibrating Pack Voltage 0x5a register properly

Please give examples with actual data before and after calibration of:

* reported pack voltage

* Ref Voltage (subclass 104, offset 8)

* AFE Pack Gain (subclass 104, offset 12)

And the expected pack voltage.

Hi Dominik,

Here is what I am seeing and this is after calibration:

Reported Pack Voltage: 15687mV

Ref Voltage: 1224.20

AFE Pack Gain: 689.03

OCV Pack Voltage measured: 15719mV

Thank you in advance!

What were the values before calibration?

Ref Voltage = 1225.10
AFE Pack Gain = 689.03

I do not have the voltages.

So EVSW only changed the Ref Voltage? Please describe exactly how you are using EVSW to calibrate pack voltage.

Hi Dominik, 

We are measuring the pack+ voltage and then writing it into the voltage calibration box under calibrate selected and then we are clicking pack voltage calibrate. Sometimes it works and sometimes it fails.

Also, we are performing this in a tester we use the following document to perform this: SLUA379E.

This board was calibrated using the tester. 

Also, what should be the accuracy of register 0x5a vs the actual pack+ measurement? At times it is within 30mv and after a sec after a 2A load it can be 500mv or more then the actual reading of Pack+.

Thank you!

0x5A doesn't actually return the present pack voltage but the last result from the internal AFE calibration as applied to vpack. This is not updated every second but part of a round robin calibration schedule. Because the information when this measurement was taken isn't available, it can't be easily compared (unless you have a steady state with constant real pack voltage). This is also the reason why you observe the large difference when you apply the 2A load.

SLUA379E suggests that pack calibration isn't necessary. I recommend not performing pack calibration or if you do, do not verify this with command 0x5a because this command won't return the pack voltage that the gauge uses for it's algorithm but instead a snapshot of the last internal afe calibration.

Hi Dominik,

What would be a good register to read to compare to the pack output?

0x09 Voltage

0x5a Pack Voltage (This is not good for pack output)

0x5d Average Voltage

0x3c - 0x3f Cell Voltage 4 - 1