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BQ27Z561EVM-011: Ra Table Update

Rowshon Munny
Intellectual 390 points
Part Number: BQ27Z561EVM-011
Other Parts Discussed in Thread: BQSTUDIO, BQ27Z561

Hi,

I am trying to see 1s Li-Ion battery characteristics using the BQ27z561EVM. The impedance profile update is showing in the Ra table within the bqStudio. From SLAU364b I am seeing the table updates according to the following figure with DOD change. Questions are:

1. What are the other parameters influencing this Ra table change? 

2. How fast the Ra table values possible to change? In terms of software and EVM module.

Thanks for your time!

  • 0
    TI__Guru 52115 points

    I would suggest you take a look at Section 4.4.6 of BQ27z561 TRM.

    Andy

  • 0 in reply to Andy Liu (BMS)
    Intellectual 390 points

    Hi,

    Thanks for your response. So, I followed the 4.4.6 in the document. Could you please help me understand:

    1. What does default Ra Max Delta= 15% mean? 

    Does it mean, suppose at any grid point the resistance value was 181 ohm then only allowable change we can see at that grid point if the resistance increases 27.15 mohm max (181 ohm * 0.15)? So, increasing the % will allow me to see more change in resistance at any particular grid?

    2. Do we need to think about the 0-255 range while configuring the % change of Ra Max Delta? If so then what is 15% in terms of the 0-255 value. 

    3. At some point in testing RaScale is reset to 1000. I saw section 4.4.7.3 of the criteria this may happen. But how can I fix it?  

    Thanks a lot for your time!

  • 0 in reply to Rowshon Munny
    TI__Mastermind 24870 points

    Hello,

    These are variables used by impedance track for resistance learning. It does not relate to RaScale. That term is used for fast scaling.

  • 0 in reply to Kang Kang
    Intellectual 390 points

    Hello Kang,

    Yes, I went through the reference manual. But can you please answer the questions I asked. I'm not seeing any explanation in the manual!! 

    Thanks!

  • 0 in reply to Rowshon Munny
    TI__Guru 51296 points

    #1: Your understanding is almost correct. The reference isn't the resistance at the present grid point but the DesignResistance 

    #2: A value of 15 means a maximum change of 15%

    #3: RaScale is just for information. Close to end of discharge, the gauge will run discharge simulations frequently (not just at grid points). If there's a mismatch between measured voltage and calculated loaded voltage (using the internal ChemID: OCV and R) then the gauge will scale cell resistance to minimize any errors in remaining capacity estimations that could lead to a sudden drop in SOC). This scaling factor is reported as RaScale (1000 means a factor 1.0). This is all automatic and doesn't need to be modified.