• Resolved

INA233: INA233 scaling constants

Part Number: INA233

Hi all,
I am trying to use an INA233EVM to measure the current and energy usage of a battery operated device.

I am able to read and write all registers, and from the data sheet I calculated the shut resistor value and the corresponding calibration register value for my application.
At this point I am reading reasonable voltage and current values, and I can also read values from the Power and Energy registers.

The problem is that I am not sure what scaling factors are used internally by the INA233 to compute these values in order to roll them back to Watts and Joules.

I followed the "Current Sensing Video series" and particularly the video 3.3 which shows the exact computations to do, but showing formulas that contain two constats (C and D).
For the values of these constants the video tell to refer to the specific device data sheet.

Unfortunately I coudn't find any useful data from the data sheet to convert the Power and Energy registers reading into SI units.

As an example I am reading:
With the Voltage scaling of 1.25mV/digit and a Current_LSB of 15.6uA this means V=4.97V and I=250uA
With these values the actual Power should be 1243uW
Instead the Power register shows a value of 3 and sometimes 4.

Of course this is due to the internal scaling, but what factor is used?
Can anyone help?

As a side note I saw that the energy register increments on average by 3.07 per sample, so it seems to be a simple "power" accumulator without scaling (or with a scaling factor of 1).

Best Regards.

  • Hello Mau,

    The information you are looking for is in section 7.5.2 of the datasheet, as highlighted below:

    So, for your example, the Power_LSB would be 25*15.6u=390u. Therefore, the power when it shows 3 is 3*390u=1170uW, and the power when it shows 4 would be 4*390u=1560uW.  These values match up nicely with your expected value.

    Best Regards,

    Mitch M, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Mitch M:

    Hi Mitch,
    Thank you very much!
    I expected a more visible "table of constants" or similar, and I missed the sentence.
    Great job!