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INA193: current measurement circuit

Jason yu
Intellectual 430 points

Part Number: INA193
Other Parts Discussed in Thread: INA194

I would like to use ina193 to design a current measurement circuit, the current is the sensor output 4 ~ 20ma current, I would like to convert the 3.3v single-chip measurable range of voltage, the following is the circuit diagram, please help us to see whether the design is reasonable, what needs Improved place.

  • 0
    TI__Mastermind 32395 points
    Hello Jason,

    Here's my analysis. You will need to choose a INA193 with a gain of 20 so that with current ranging from 4-20mA, this will create sense voltages of 20mV to 140mV. These will be gained up to 560mV and 2.8V. This is your best option to achieve full-scale range on your output given a power supply of 3.3V. This will result in 7% error for your 4mA measurements since the Vos_max of the part is 2mV.

    Is there not common-mode voltage at the Vin+ pin? Basically is your pressure sensor acting as a current source? How fast will the pressure sensor output change? Also, I assume the output filter is for driving and ADC. You will want to make sure that the 193 will have enough BW to drive ADC and whatever sampling frequency the ADC is set to.

    Peter Iliya
    Current Sense Applications
  • 0
    TI__Mastermind 26335 points
    Hello Jason,

    Thank you for considering to use Texas Instruments in your design. The voltage for your supply is adequate, but I would recommend placing a .1uF bypass capacitor on it for added stability in case there are any transients on the supply. The 7 ohm sense resistor should only produce 0.028V-0.14V differential at the input which is well within the input differential tolerance and will produce an output within output swing limit. I presume that you are striving more for accuracy than for lowered power dissipation from the shunt resistor, since you could potentially use smaller sense resistors with a larger gain option. If you would like to reconsider that, page 3 of the ina193 datasheet lists all other devices with the same architecture but different gain values. Also you might consider using a 7.5 ohm resistor as this will still produce an output within tolerance and is a common .1% resistor value.

    Otherwise, with the design constraints you have listed above, this design seems reasonable.
  • 0 in reply to Patrick Simmons
    Intellectual 430 points

    Hi Patrick,

    Thanks for your answer,I used to consider using INA194 and 3 ohm sense resister ,the gain is 50.but when the current is 4ma,the Vsense is 12mV.According to the datasheet, whether the sense resister voltage below 20mV will affect the accuracy.and one more question i wanna ask,Is this RC filter necessary?

    bset regards，

  • 0 in reply to Peter Iliya
    Intellectual 430 points
    Hi Peter,
    thanks for your answer,the pressure sensor is 4~20ma output current，I think the VIN+ change by the current and senser resister.The response time of the sensor is less than 5ms. Is this RC filter necessary? I just want to use it to improve the stability of the output voltage.
    best regards,
  • 0 in reply to Jason yu
    TI__Mastermind 26335 points
    Hello Jason,

    The filter is not absolutely necessary for your design. However, if some higher frequency signals manage to couple onto your trace and you would like to ignore those, the RC filter provides a means to do so.
  • 0 in reply to Patrick Simmons
    Intellectual 430 points
    Hi,Patrick
    i wanna ask you one more question,can you tell me the Power consumption of INA194，the power supply is 3.3v.
    thanks
  • 0 in reply to Jason yu
    TI__Mastermind 32395 points
    Jason,

    Please see my answer here:
    e2e.ti.com/.../2392925

    Short answer is power = VCC*IQ = 3.3V*700uA = 2.31 milli-Watts

    Peter Iliya