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BQ78350-R2-DEVICE-FW: Power consumption in sleep mode - Electronics Load affected by IPSCALE ?

Pietro Vignali
Intellectual 925 points

Part Number: BQ78350-R2-DEVICE-FW

Hello,

We are measured that the self consumption of a battery pack with a bq78350-R2 based BMS is approx around 150uA.

After programming the FuelGauging-CEDV Cfg-Electronics Load as 50 units (= 150uA) we have conducted some test with the pack left for several hours in sleep mode.
After several hours (> 24h) we have realized that the gauge is decreasing the remaining capacity at a rate of approx 1.7~1.6mAh.

How does the gauge is calculating this data ?

The other parameter involved, FuelGauging-CEDV Cfg-Self Discharge Rate, is set = 2, corresponding to 0.02%/day that we have measured over a long period, and the actual temperature is always below 25 degC.

I have a suspect: this pack has IPSCALE set = 0x1, to scale the currents by a factor of 10.


Is it maybe that this factor is used also to scale the calculation of the self consumption when the pack is inactive, and so instead of accountin 150uA, it is accounting 1.5mA ?

Thanks in advance

Pietro

  • 0
    TI__Guru* 81034 points

    Hi Pietro,

    I think you have the right idea. When using IPSCALE of 0x1, all data flash parameters for current or capacity need to be scaled by 10.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 925 points

    Thanks Matt, I will immediately make a try!

    Regards

    Pietro

  • 0 in reply to Matt Sunna
    Intellectual 925 points

    Hello Matt,

    I scaled the Electronics Load accordingly, from 50 down to 5, as suggested.
    I RESET the battery and left it on the shelf disconnect.

    At the beginning of the test the REMAINING CAPACITY was reporting 4200mAh

    After almost 24h, it is still 4200mAh, instead of being decreased by approx 0.150mAh * 24 = 3.6mAh.
    I was infact expecting to read at least 4197mAh.

    I will continue to keep the battery on the shelf for a more time over the weekend to see if it will report correctly after a long period of time, but this time I have the feeling that it is accounting just a real sel-consumption of 0.015mA (5 x 3 uA).

    Am I doing something wrong, or there is some hidden trick ?

    Thanks in advance
    Pietro

  • 0 in reply to Pietro Vignali
    TI__Guru* 81034 points

    Hi Pietro,

    Let me know what you see after the weekend and I will also look into this more to see if I am missing anything.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 925 points

    Hello Matt,

    After several hours of shelf-life in sleep mode I saw the effects and I confirm that the Electronics Load need to be scaled according to IPSCALE.

    The fact that I did not see results after some hours is becaiuse the Remaining Capacity has a precision that depends on IPSCALE as well, and so I can only read a change every 10mAh...

    Thanks so much

    Pietro