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BQ27531-G1: ChemID characterization

Part Number: BQ27531-G1
Other Parts Discussed in Thread: GPCCHEM, BQEVSW, BQSTUDIO

We use the TI battery gauge bq27531 in one product line. We have succesfully completed the ChemID characterization with our test bench and the GPCTool for the first batch of battery cells. However, we need to use another battery cell now which apparently differs in its electrochemical properties. The GPCTool does not find a good match. It ends up with a deviation of just around 2,5 - 3,5% from run to run. (For the first batch of batteries, repeated use of GPCTool led to deviations of 'only' 1,5-2,2%)

Best chemical ID : 2079 Best chemical ID max. deviation, % : 3.35
  
Summary of all IDs with max. DOD deviation below 3%  
  
Chem ID max DOD error, % Max R deviation, ratio
0 0 0
  
Warning: Deviation is above recommended level. New chem ID needs to be released for this cell. Please contact your TI representative to send the cell to Dallas for characterization

 

So, the question is: Do we need a new chem ID characterized by your engineers in Dallas? What are the conditions for that?

Best regards, Nils Larsen

  • Hello Nils,

    Can you post the cell manufacturer model info? Please check that the cell did not have any protection circuit when data was collected. I sent you a friend request so that you can message me directly if you do not want to post details on the forum.

  • Thank you. The protection circuit was in fact connected, but I compensate the voltages before submitting to the GPCCHEM tool. I'll send you the datasheet as a private message.

    My procedure for compensating the protection circuit is as follows:
    I ran a pre-experiment adjusting the current in the relevant charging/discarging range in 17 steps from -500 mA to +600mA, comparing the bare cell voltage (measured with a Fluke 175 multimeter) with the voltage at the terminals of bq27531. A very good fit ist possible if I compensate using a resistance of 103mOhm. So the submitted voltages are the bare cell voltages +/- 1 mV, at least if Fluke 175 as a reference is good enough?

  • Hello Nils,

    The characterization process will require multiple new cells with the protector removed and takes months. I would recommend getting logs with bare cells to double check that everything was accounted for correctly.

  • Ok. We will surely do the double checking first. Could you anyway forward me the details of the characterization process: Are we talking about 2, 3 or more months? What will it cost us? Will we have to upgrade the firmware of the bq27531-chip to use the (new?) ChemID? And if yes, how will we get that firmware upgrade (what filetype).

  • Hello Nils,

    There is a queue for cell characterization and depending on the current load it can take anywhere from approximately 2 to 6 months. All characterized batteries will be listed in the Chemistry database and made available in bqStudio/bqEVSW. The firmware will not change but the new ChemID will need to be programmed into the firmware and a new golden image will need to be created.