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BQ40Z50-R1: mVh vs mAh modes

Jerry%20Leung
Intellectual 905 points
Part Number: BQ40Z50-R1

Hi Team,

I have a customer who is using the BQ40Z50-R1 and have an application question between using the mAh mode vs mVh mode they would like to get some insights on:

The product team came up a requirement to use the battery capacity to measure the power used in a certain operation, and use the information to constrain against the same operation in the future. I found there are two battery modes (CAPM (Bit 15): CAPACITY Mode) to configure, the mAh and the mVh. I would imagine the mAh mode is more direct because that is the unit used by the battery manufacturer. However, is the same amount of mAh can be drawn to complete the operation from the battery when it is 100% comparing to 50%? In terms of that concern, I think mVh may be closer to what I need. Am I correct?

I went ahead and tried to change to mVh. I noticed the SoH changed from 88% to 44%. Is there other setup I need to do when changing this configuration?

Thanks in advance for the help and best regards,

Jerry

  • 0
    TI__Mastermind 25955 points
    Hi Jerry,

    Changing from the default configuration of 0 for CAPM (Bit 15) that reports in ma or maH to 1 that reports in 10 mW or 10 mWh will have effects in other registers of the device. To find these, please search the TRM for CAPM. There will be an if statement that describes the effect on the other parameter based on whether CAPM = 0 or CAPM = 1.

    For example, if CAPM = 1, 0x04 AtRate() will report in 10 mW.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    TI__Intellectual 905 points
    Hi Bryan,

    Thanks for confirming the CAPM configuration change does affect other parameters. Could you help provide some insights to the following questions for our customer?

    1. When comparing the amount of capacity consumed starting from 100% and 50%, is mAh or mWh going to give me more consistent measurement?
    2. After changing the CAPM parameter from 0 to 1, why is the SoH changed from 88% to 44%?

    Thanks for the help and best regards,
    Jerry
  • 0 in reply to Jerry%20Leung
    TI__Mastermind 25955 points
    Hi Jerry,

    1. mAh will give a more consistent measurement because voltage and current are not measured at exactly the same time. By using mAh, you will only be using one of these two measurements.

    2. SoH = FCC / Design Capacity

    Has your device gone through a learning cycle? FCC will not be set before a learning cycle is complete.

    Please send your device gg.csv so we may analyze further. Device capacity not being set in cWh may be the root cause.

    Sincerely,
    Bryan Kahler