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INA271: OUTPUT VOLTAGE / AMPS IS DIFFERENT IN EACH BOARD .. HAVING THE SAME CIRCUIT AND COMPONENTS ... ( WITH SAME 1A CURRENT FLOW)

Part Number: INA271
Other Parts Discussed in Thread: INA282

Hi,

Am using INA271 Current sensing amplifier in by dual phase synchronous buck design ..My shunt resistor value is 2 milli ohms ..

am getting different output voltages corresponds to the input current .. each and every boards output sensing voltage for 1A current is different .. so i cannot fix a particular value in my code ..

am confused what to do..

current sensing : High side - 48v DC

shunt resistor   : R002 copper shunt .

supply voltage  : 10v dc

output voltage /amps current is different for every board .. please help solving the issue ..

parts used per board : 2 nos 

Best regards,

Vasantharaja

  • Hello Vasantharaja,

    If your shunt resistor is 2 milli-Ohms and the current is 1A, then the sense voltage is 2mV, which is most likely the problem. The INA271 is specified to have an input offset voltage (Vos) of +/-0.5mV typical and +/-2.5mV maximum. Even if each of your boards contains INA271 devices with an offset of +0.5mV, then you will see 25% error immediately. Most likely, the INA271 devices have offsets around +-0.5mV and thus you can see total errors of 10%, 15%, 30%, or even 100% among your boards since you are sensing a voltage that is essentially the same as the offset of the device.

    To solve this issue, you could increase the size of your shunt resistor, so the offset error is reduced, or you could select a device with a much lower offset such as the INA282 (Vos typical = +/-20uV; Vos maximum = +/-70uV).

    Sincerely,
    Peter Iliya
    Current Sensing Applications
  • Hello Peter,

    so many thanks for your prompt support ... 

    what will be the  suggested shunt resistor value for the INA271 ( FOR CURRENT FROM 0 - 30A).. 

    i try changing them to .020 ohms so that i can get 1*.020 = 20 mV  ( or other wise i have to increase it further ) ?

    wheather the part suggested by INA282 WORKS With 2mv (r002. - resistance @ 1A for sure) ?

    thanks in advance..

  • Vasanth,

    Please correct me here, but is your high-side/common-mode voltage +48V or -48V? Just so I'm clear.

    Anyway, I would recommend a shunt resistor of 16.2 mOhm. I calculated this with the following:
    Vs = 10V
    Current = 0 to 30A
    Max Vout = {Vs - 0.2V}, over ambient temp = -40c to +125C
    Gain = 20V/V

    Thus, max sense voltage (Vsense_max) = 9.8V/(20V/V) = 490mV.

    Max shunt resistor = 490mV/30A = 16.333 Ohms --> choose 16.2 mOhm standard value.

    With this shunt resistance you will most accurately be able to measure from 1.234A to 30A. This is because you get best accuracy when Vsense>20mV. You can read about this here:
    e2e.ti.com/.../3592.measuring-vsense-20mv-with-the-ina270-and-ina271

    Sincerely,
    Peter Iliya
    Current Sensing Applications