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INA226: Calibration Register

Qi Liu
Expert 6345 points
Part Number: INA226


Hi, support team

My customer has the questions as follow:

What is the calculation process of Calibration Register value?
The value I calculated according to datasheet is inconsistent with the theoretical value.

The calculation process of our former engineer with 1mΩ sampling resistance is as follow:

If I change it to 2mΩ now, could you tell me what to do with steps 3 to 4?


Thanks so much.

Best regards,
Yuki

  • 0
    TI__Expert 4720 points

    Hello Yuki,

    Qi Liu said:
    The value I calculated according to datasheet is inconsistent with the theoretical value.

    How is the theoretical value calculated?

    There are a few issue's with the code. First the INA226 max Vshunt is  81.92 mV, so VSHUNT_MAX must be changed to .08192, this will give you a different Max current for your Rshunt. Also under number 5 the first equation should read Cal = trunc (.00512/(Current_LSB * Rshunt)). Rshunt is also equal to 20 mOhm, while you said the 

    I will go over everything again for your 2m ohm shunt resistor:

    VBUS = 9 V, VSHUNT_MAX = .08192 V, RSHUNT = .002 Ohm

    MaxPossible_I = VSHUNT_MAX/RSHUNT = 40.96 

    // if this maximum current is ok then great, if not select different Rshunt to satisfy your Max current, ie Rshunt = .08192/Max_Current

    Current_LSB = MaxPossible_I/(2^15) = .00125

    // or Current_LSB = MaxPossible_I/32768

    Cal = .00512/(Current_LSB * Rshunt) = 2048 (0x0800)

    If you have any other questions please reply

    Regards,

    Castrense