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Original question:

BQ27421-G1: What is the initial accuracy of the SOC reported by the BQ27421-G1 Fuel Gauge

BQ27421-G1: What is the importance of max DOD% shown in the GPCCHEM Report

Vidyasagar Kunala
Prodigy 200 points
Part Number: BQ27421-G1
Other Parts Discussed in Thread: GPCCHEM

Hi,

I have recently performed relax-charge-relax-discharge cycle with my 450mAh LiCoO2 battery (4.2V max voltage) using BQ27421-G1A EVM and uploaded the log on GPCCHEM. 

Report given best chem ID matching with my battery as 3136 with a max deviation of 1.65%. Apart from that report also given below values

Generic Chem ID Device/ Voltage/ Chemistry max DOD error, %
3142 bq27421-G1D: 4.4V LiCoO2 12.71
354 bq27411-G1C: 4.35V LiCoO2 14.65
128 bq27421-G1A: 4.2V LiCoO2 15.83
312 bq27421-G1B: 4.3V LiCoO2 18.91

I have some queries based on the report

1. What is the significance of max DOD error% ?

2. What will be the inaccuracy in the SOC reported by the BQ27421-G1A gauge with my 450mAh battery in the filed ?

3. Why max DOD error% is less with G1D & G1C compared to G1A when my battery is supporting max voltage of 4.2V ?

4. What is the importance of Temperature values in the log file to GPCCHEM tool. Will it impact max DOD error% ?

Let me your feedback.

Thanks & Regards

Vidyasagar


Device / Family #1 Generic Chem ID Device/ Voltage/ Chemistry max DOD error, %3142 bq27421-G1D: 4.4V LiCoO2 12.71354 bq27411-G1C: 4.35V LiCoO2 14.65128 bq27421-G1A: 4.2V LiCoO2 15.83312 bq27421-G1B: 4.3V LiCoO2 18.9
1

  • 0
    TI__Mastermind 24870 points
    1. max DOD error helps you determine if the ID is an appropriate fit. Refer to the GPCCHEM documentation for more details. If this is less than 3%, you can use that ID.

    2. You really have to evaluate this on an EVM

    3. It depends on the shape of the OCV curve that the tool calculates. The recommendation is to go with GPCCHEM.

    4. Temperature helps us do compensation.
  • 0 in reply to Kang Kang
    Prodigy 200 points

    Hi Kang,

    Regarding question 2, can you elaborate how can I test SOC accuracy on the EVM with my 450mAh battery.

    Regarding question 3, I'm saying that my battery supports a max voltage of 4.2V & BQ27421-G1A also supports the same. Whereas BQ27421-G1D & G1C supports max battery voltages of 4.4V and 4.35V. My question is how max DOD error% is less with G1D & G1C compared to G1A ? 

    Can you tell me what is the exact difference in the chemistry supported by G1A, G1B, G1C & G1D devices so that I can ask my battery vendor accordingly.

    Thanks

    Vidyasagar

     

  • 0 in reply to Vidyasagar Kunala
    TI__Mastermind 42535 points
    A standard charge relax dsg relax cycle at a C/2 rate is usually the method to test accuracy.
    You have selected certain ROM based gauges which are less expensive compared to our other programmable gauges
    In each of these versions, the chem ID is fixed. As batteries are developed with higher max chg V, newer device versions with chem ID that support the higher chg voltage were released. The DS on each of the versions should tell you what max V is supported by each device.