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BQ27426: The mechanism of averagecurrent() calculation

Part Number: BQ27426
Other Parts Discussed in Thread: BQ27220, BQ40Z50, BQ4050, , BQSTUDIO

Hi team,

Background

The battery is in relax mode and start to charge

Issue

Found that the current value they read from the gauge register is not equal to the actual value. It delays about 3-4 seconds.

Question

Is that because the current value in the register is the average result?

I check the TRM, it is said that the averagecurrent() in normal mode is Qpasscharge(in 1s)/1s, but it didn't show how the averagecurrent calculate in relax mode?

Besides, is the below picture means "Current" value is the average result of pass 14s "averagecurrent()"?

  • Btw, I also want to check is bq27220 the CEDV version of system side BQ27426? Just like the relationship between BQ4050 and BQ40Z50. 

    Thanks and look for your reply!

  • Hello Kailun, 

    When the gauge is in sleep mode the registers get updated only once every 20 seconds, whereas when the gauge is in normal mode the registers get updated every 1 second. Please refer to sections 2.4.4 NORMAL Mode and 2.4.5 SLEEP Mode in bq27426 Technical Reference Manual

    If you are using BQStudio, the 3-4 second delay you are experiencing could be due to the fact that BQStudio logs data from the registers every 4 seconds by default. You can change this rate in BQStudio, but it is not recommended to change this below 1 second as the registers on the gauge only update every 1 second. Please see the image below from bq27426EVM-738 Single-Cell Impedance Track Technology

    To answer your follow up question, the relationship is not the same. The BQ27220 is a single cell gauge like the BQ27426, but there are differences such as CEDV versus Impedance Track, system side versus pack side, the max battery capacity, the hardware, and others.

    Regards, 

    Jonny T.