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INA233: INA233

Sadashiva Kamath
Expert 1135 points
Part Number: INA233

We're evaluating using INA233 in our design.


Design Parameters:

a) Max. expected current = 98.3mA. So, Current_LSB = 3.00 E-06

b) VBUS voltage = 5V +/- 10%

c) High-Side Shunt Resistor = 100mOhm, 0.1%

d) So, CAL = 17066 => Hex = 42AA

Question:
1) Is Resnse resistor & CAL values are fine? Any suggestions on Rsense resistor value?

2) X = 1/ m * (Y * 10-R - b). Y = a 2-byte, two's complement integer received from the device. Do we need to convert two's complement integer that is received from the device while sustituting values in X = 1/ m * (Y * 10-R - b)? Can you elaborate on this?

  • 0
    TI__Mastermind 26730 points
    Hello Sadashiva,

    Thanks for coming to the forum and asking your questions. We hope to solve them well.

    To address your first question, there seems to be an error in you CAL value. If I calculate CAL according to Equation 1 of datasheet, then I get 17066.66, which I would round to 17067 (0x42AB).

    Aside from this, this calibration value could be fine, but you could sacrifice some power dissipation and increase your shunt resistor so it could read shunt voltage up to device’s full-scale +-81.9175mV. Right now, VSHUNT = 9.83mV at your highest expected current. Increasing your shunt resistor would bring down error on the smallest current you need to sense and increase signal to noise ratio, but overall these are just general guidelines. I am unaware on what your system is really for.

    For question 2, the operation of using these coefficients in the PMBus is a part of the PMBus Power Management Protocol www.pmbus.org/.../CurrentSpecifications. This could give you plenty of detail, but essentially you are correct that you need to convert the Y byte data into a decimal integer before actually calculating out equation 3 in datasheet. Please know that this communication protocol is optional and you could read the registers through the I2C protocol and more simply multiply these values by the LSB to obtain real-world values.

    Hope this helps and please post back if you need more information.

    Sincerely,
    Peter Iliya
    Current Sensing Applications
  • 0 in reply to Peter Iliya
    Expert 1135 points

    Thanks Peter for details.

    I got CAL value as 42AA in my earlier calculation. As you mentioned, 42AB is the correct one. I used MS excel for calculation. MS Excel truncated 17066.66 as 17066. It was the reason for CAL value of 42AA :)