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BQ27Z561-R2: For Enhanced Resolution Gauging for Low Current Applications Using Scaling

user1567465
Intellectual 260 points
Part Number: BQ27Z561-R2

Tool/software:

Dear sir,

 We set the parameters according to SLUA792 when the sensor resistance is changed by a calibration ration of 20x (from 1m Ohm to 20m Ohm).
 SLUA792 states "Parameters with units of mA, mW or mAh should be multiplied by the calibration ratio accordingly.".
 For the BQ27Z561-R2, the following parameters are considered candidates. (refer to sluuc54c)


  No.  Address / Class / Subclass / Name
   1. 0x4645 / Settings / BTP / Init Discharge Set
   2. 0x4647 / Settings / BTP / Init Charge Set

   3. 0x46CD / Advanced Charge Algorithm / Pre-Charging / Current
   4. 0x46CF / Advanced Charge Algorithm / Maintenance Charging / Current
   5. 0x4713 / Advanced Charge Algorithm / Termination Config / Charge Term Taper Current

   6. 0x4721 / Gas Gauging / Current Thresholds / Dsg Current Threshold
   7. 0x4723 / Gas Gauging / Current Thresholds / Chg Current Threshold
   8. 0x4725 / Gas Gauging / Current Thresholds / Quit Current

   9. 0x4663 / Gas Gauging / Max Load / Max Load Current
 10. 0x4666 / Gas Gauging / Design / Design Capacity mAh
 11. 0x4668 / Gas Gauging / Design / Design Capacity cWh

 12. 0x4186 / Gas Gauging / State / Qmax Cell 1
 13. 0x418F / Gas Gauging / State / Current at EoC
 14. 0x4191 / Gas Gauging / State / Avg I Last Run
 15. 0x4193 / Gas Gauging / State / Avg P Last Run
 16. 0x419B / Gas Gauging / State / Max Avg I Last Run
 17. 0x419D / Gas Gauging / State / Max Avg P Last Run

 18. 0x465B / Power / Sleep / Sleep Current
--------------------------------------------------------------------------------------------------------------------------------------
 19. 0x46AF / Advanced Charge Algorithm / Low Temp Charging / Current Low
 20. 0x46B1 / Advanced Charge Algorithm / Low Temp Charging / Current Med
 21. 0x46B3 / Advanced Charge Algorithm / Low Temp Charging / Current High

 22. 0x46B5 / Advanced Charge Algorithm / Standard Temp Low Charging / Current Low
 23. 0x46B7 / Advanced Charge Algorithm / Standard Temp Low Charging / Current Med
 24. 0x46B9 / Advanced Charge Algorithm / Standard Temp Low Charging / Current High

 25. 0x46BB / Advanced Charge Algorithm / Standard Temp High Charging / Current Low
 26. 0x46BD / Advanced Charge Algorithm / Standard Temp High Charging / Current Med
 27. 0x46BF / Advanced Charge Algorithm / Standard Temp High Charging / Current High

 28. 0x46C1 / Advanced Charge Algorithm / High Temp Charging / Current Low
 29. 0x46C3 / Advanced Charge Algorithm / High Temp Charging / Current Med
 30. 0x46C5 / Advanced Charge Algorithm / High Temp Charging / Current High

 31. 0x46C7 / Advanced Charge Algorithm / Rec Temp Charging / Current Low
 32. 0x46C9 / Advanced Charge Algorithm / Rec Temp Charging / Current Med
 33. 0x46CB / Advanced Charge Algorithm / Rec Temp Charging / Current High
--------------------------------------------------------------------------------------------------------------------------------------
 34. 0x4691 / Gas Gauging / IT Cfg / User Rate-mA
 35. 0x4693 / Gas Gauging / IT Cfg / User Rate-cW
 36. 0x4695 / Gas Gauging / IT Cfg / Reserve Cap-mAh
 37. 0x4697 / Gas Gauging / IT Cfg / Reserve Cap-cWh

 38. 0x4660 / Power / Sleep / Deep Sleep Current

 39. 0x4206 / Lifetimes / Current / Max Charge Current
 40. 0x4208 / Lifetimes / Current / Max Discharge Current
 41. 0x420A / Lifetimes / Current / Max Avg Dsg Current
 42. 0x420C / Lifetimes / Current / Max Avg Dsg Power

 Parameters No.1 to No.18 are changed to those setting value of 20 times.

 The settings of parameters No.19 to No.33 are not changed.
 Because, for example No.23. 0x46B7 / Advanced Charge Algorithm / Standard Temp Low Charging / Current Med's default value is 4004 mA.
 This value by 20 times will exceed the set range (from 0 to 32767).

 Parameters No.34 to No.42 are not changed as their default values are 0.

 Are those settings correct?
 Are there any parameters that do not need to be changed?
 And, are there any other parameters that need to changed?

Best Regards,

  • 0
    TI__Mastermind 24901 points

    Hello, 

    When changing the sense resistor, I recommend re performing the current calibration process. When you perform the current calibration process the gauge should update the appropriate parameters to reflect the new sense resistor. 

    Regards, 

    Jonny. 

  • 0 in reply to Jonny
    Intellectual 260 points

    Dear Jonny

     Thank you for your reply.
     Which of the above No.1 to No.42 are appropriate parameters?
     And, are there any other appropriate parameters?

    Best Regards,

  • 0 in reply to user1567465
    TI__Mastermind 24901 points

    Hello, 

    The values that should change are the CC Gain and the Capacity Gain.

    Regards, 

    Jonny. 

  • 0 in reply to Jonny
    Intellectual 260 points

    Dear Jonny

     Thank you for your answer.
     We confirmed that the CC gain and the Capacity Gain changed when we performed the current calibration process.

     Next step, we will perform the lerning cycles process.
     We use 400mAh of 1cell Li-pol battery.
     And, we use 20mOhm of the RSENSE resistor in order to measure with very small active current (200uA).
     Accordingly, we change that the parameter (No.10 0x4666 / Gas Gauging / Design / Design Capacity mAh) from 400mAh to 20 times that, 8000mAh.
     Which parameters from above No.1 to No.42 need to changed to 20 times the original design value simulaly No.10?
     And, are there any other parameters other than No.1 to No.42 that need to be changed to 20 times?

    Best Regards,

  • 0 in reply to user1567465
    TI__Intellectual 2020 points

    Hello,

    We are looking into this and will get back to you soon.

    Regards,

    Siddharth

  • 0 in reply to Siddharth Venkatesan
    TI__Mastermind 24901 points

    Hello, 

    The design capacity is not a parameter you should change for this, please do not change the design capacity to a value other than what is specified by your cell datasheet. The following Application Note goes over everything that needs to be changed when you use a higher value sense resistor to achieve better resolution. Please see this Application note. 

    Regards, 

    Jonny.