BQ27426: Regarding bqStudio configuration

Hello,

This question has been assigned within the team and will be reviewed and followed up with a application engineer when possible. In the meantime please attach any associated .log/.gg files associated with the projects

Thank you,
Alan 

This is because bqStudio applies min/max thresholds to CC gain and all other parameters if you want to manually change them. If the calibration function calculates values outside this range then bqStudio will not enforce these thresholds.

Are you using a very large sense resistor?

You can read the 4 bytes for CC gain directly from data memory using advanced comm, which gives you the 4 bytes that correspond to the CC gain floating point value which was generated by calibration. And you can then write these 4 bytes back to a gauge in advanced comm (using the data memory write access sequence described in the TRM). This circumvents the min/max limitations.

Hi Dominik, 

Ann account can't reply you. Please check our test. 

1. How to read/write using Advanced Comm?

I referred to Table 6-1 Extended Commands and Section 7.4.5.2.1 Coulomb Counter Sense Resistor (CC) Offset, Gain, Delta in the TRM, and followed the steps below in the Advanced Comm interface to try reading CC Offset, CC Gain, and CC Delta.

a. Start Register = 61, Bytes to Write = 00 → Write
b. Start Register = 3E, Bytes to Write = 69 00 → Write (Subclass 105)
c. Start Register = 3F, Bytes to Write = 00 → Write (Block offset 0)
d. Start Register = 40, Bytes to Write = empty → Read, Number of Bytes to Read = 32

The following data was read back:
00 00 0B D6 7D 1A F7 4D 91 30 51 20 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

How should this data be interpreted?
Are there any issues with the steps above?

2. Are you using a very large sense resistor?

This is a follow-up question.

During calibration, a DC loader was used to apply a 1 A current.
After calibration, the CC Gain was approximately 0.2194, and CC Delta was 261754.4063.

After applying the calibrated gauge table to our product with a 1S3P battery configuration, we found that the current reported by the gauge was approximately 3× higher than the actual measured current.
Therefore, during calibration, the applied current was divided by 3 (i.e., 333 mA), which resulted in a much smaller CC Gain value.

This behavior also seems unusual to us.
Do you have any suggestions on this?

cc Terry Hu Ann Hu 

CC Gain is at offset 4. The data from your example is 7D 1A F7 4D. This is the 4-byte hexadecimal representation of a Xemics format floating point number and equals 0.0756670013.
The gauge automatically calculates CC Delta so you can ignore this. All you have to do is set CC Gain.

You can convert between Xemics float and hex with this spreadsheet: 5504.Float.xlsm

Writing values is a bit more complicated as you have to calculate a check-sum. You can either follow the example in the TRM https://www.ti.com/lit/ug/sluubb0/sluubb0.pdf, 4.1 Data Memory Parameter Update Example or use a whole block update as described in https://www.ti.com/lit/SLUA801

Calibration is independent of number of parallel cells. The gauge simply measures the voltage drop over the sense resistor and bqStudio calculates a CC Gain factor which converts the 16-bit integer result from the CC ADC to current in mA.

There must be a calibration setup problem on your side where the current is off by a factor of 3.

• "The original gauge table provied by TI FAE(ChemID 2141)"
• "The calibration gauge table(1A calibration, no scaling)"
• "Comparison between the original and calibration tables"

Only calibration-related fields were updated; the chemistry data remains unchanged. 

Original_TI_FAE_ChemID2141.csvCalibrated_CC_1A_NoScaling_ChemID2141.csv

cc Terry Hu Ann Hu 

A CC Gain of 0.054 seems low. What sense resistor are you using?

VatChgTerm depends on the measured voltage when the gauge detects charge terminations. It looks reasonable but I'd have to see the voltage measurement when the current drops below the current given by Taper Rate.