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INA381: INA381 Error Analysis, shunt resistor limit

Huite Jan Hak
Prodigy 20 points
Part Number: INA381

Hi,

The online  INA381 Error Analysis does not allow you to enter a shuntresistor > 100mOhm

I have the following setup LNA381A4:

Sensed Current Range: 0mA till 30mA

Shunt: 220mOhm

Supply Voltage 3.3V

Common Mode Voltage:0V

Operating Temperature: 20±5°C

It it possible to provide me with a Error Analysis chart for this situation?

Or could you provide a tool which allows me to calculate situations without the limit in the online tool?

HJ

 

  • 0
    TI__Mastermind 26515 points

    Huite,

    I do not have a calculator for you but we can go through the analysis.

    First please be aware this current sensor has an input bias current at each pin and is dependent on two things, VCM and Vsense.  From figure 20 of the datasheet you can see that it is lower with VCM ~0V.  Vsense will change current as their is an impedance between the input pins of about 2.5kΩ.  So as Vsense increases you will get a current between the two pins.

    Since the specification of VOS is specified to be 150µV at VCM = 0V and you are using it at 0V you do not need to included the CMRR calculation.  For PSRR the calculation is (5V-3.3V)*40µV/V = 68µV.  Temperature drift max is 1µV/°C  therefore we add 5µV.  Worst case VOS = 223µV.

    VOS will equal to about 1mA of error.  At low inputs this value is very high and at your max of 30mA it is about 3.3%.

    For gain error you have to add 1% along with your resistor error tolerance.

    Hope this helps.  We also have training video that can guide you through the calculations.

  • 0 in reply to Javier Contreras4
    Prodigy 20 points

    Javier,

    Thank you for the clarifcation, it helped and I have enough information for now.

    Huite Jan