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bq27741-G1 Questions

Other Parts Discussed in Thread: BQ27741EVM, BQSTUDIO

I have some questions that I was not able to resolve by looking at the documentation available.  They are as follows:

 

1. Using I2C we are reading standard command data (flags and capacity remaining).  Our code uses the following sequence [start condition][slave address+write][command][stop condition] .. wait [read command][data Byte1][dataByte2][stop condition].  We monitored the I2C UBS in the TI development kit (bq27741EVM) and noticed it ONLY issues a stop command at the end.  Is this the recommended to not issue a stop command following the initial write or does it even matter?  It seems to work okay the way we implemented it.

 

2. We left the “chem_id” parameter setting at its default value of 0x1280 (as per bqStudio).  Using the bqStudio application the internal chem_id database shows our specific cell part number (UF103450P) as chem_id 0x0105.  Changing the chem_id would involve an extra step during the manufacturing process that we’d like to avoid unless absolutely required.  Will there be a huge accuracy change in using the ID for our cell versus the default value?

 

3. We understand that to maximize battery capacity accuracy the fuel gauge requires a “learning cycle”.  What exactly does that entitle?  Full charge/discharge cycle?  Charge or Discharge cycle?  Also, is there a quick way to get say 5% accuracy?  We are trying to minimize manufacturing steps.

 

Thanks

  • 1. Both work. Please make sure that your host follows the bus free timing requirements from the datasheet.
    2. This can only be answered if you provide a charge/relax/discharge/relax log with current, voltage and temperature. Battery type number is not necessarily a guarantee for matching chemistry. Follow http://www.ti.com/tool/GPCCHEM to identify the actual chemistry for your battery.
    What is your requirement for SOC accuracy?
    3. A learning cycle is a well defined charge/discharge step that you only have to perform once to obtain the real chemical capacity and impedance of your cell. Assuming other cells are from a similar batch, you don't have to do this for each cell. If you don't do this then the accuracy will be compromised until the gauge learns the cell characteristics (during regular use). See www.ti.com/.../slua597.pdf for details.