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INA233EVM: Current from read_iout (8C reg) doesn't correspond to value calculated using Vshunt

Swetha George
Prodigy 20 points
Part Number: INA233EVM
Other Parts Discussed in Thread: INA233

Hi,

Firstly, I have an issue with calculating the value for current using the value from the 8C register. I am using i2c/PMBus (little endian format) commands to read and write to the registers. I multiply the decimal value of the hex in 8C with the current LSB as mentioned in the manual but the value I obtain doesn't match what I feed into the shunt resistor or the value obtained using Vshunt (D1 reg). Would somebody be able to help me with this?

E.g. 8C = 0x11 0x01 D1 = 0x56 0x03 and my Current LSB is 0.24414mA/bit. Using value in D1 I get current = 0.034 A, what would be the value using register 8C ?

Secondly when I powered up the device the registers for current and voltage show values close to FFFF despite resetting the calibration register and resetting the device. The current and voltage should be 0, is there a way to clear these registers?

Thanks,

Swetha G

  • 0
    TI__Mastermind 26660 points
    Hello Swetha,

    I hope to help you out with this. In order to get the current value reading in terms of milliamps, you have to multiply the decimal value of register 8Ch by the Current_LSB. For little endian this makes 8Ch = 0x0111 (I believe this is how you are writing it). 0x0111 = 273 dec and 273 dec * 0.24414mA/bit = 66.65 mA. So I can see why you are concerned.

    1. Are you using the INA233EVM and its GUI or are you interfacing with the INA233EVM using your own software? If you are using our GUI could you post what the GUI is reading out for VSHUNT, VIN, and IIN?

    2. What is your shunt resistor value? What is supposed to be your Vshunt and current?

    3. How are you connecting your Rshunt to the EVM? There could be extra wire resistance affecting your measurment.
    4. Can you take a voltage measurement at the inputs of the INA233

    Sincerely,

    Peter Iliya
    Current Sense Applications
  • 0 in reply to Peter Iliya
    Prodigy 20 points
    Hi, I was able to resolve the issue. The error was due to writing into the registers in the wrong format. Thanks for your help!