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INA103: Problem by measuring low currents with INA103

Leonard Henkel
Prodigy 10 points

Part Number: INA103

Tool/software:

Dear TI_Forum,

I’ve got a problem with a circuit using a INA103KU.

I want to use the INA to measure current from 0 to 50mA in both directions (current from INAs Input+ to Input- and the other way around). The supply for the INA is +-14V ,I am using the internal 60,6 Ohm gain resistor and a external 1Ohm 1W shunt resistor.

 

The measurement is working fine for current from 50mA to around 5mA in both directions.

But for current smaller 5mA I’ve only got correct values for current in one direction. In the other direction the values are incorrect (and slowly falling).

 

I hope I’ve provided enough information for you to understand my problem.

Did you have some experience with this kind of problems ? Can you help me with this ?

If you need further information, please contact me.

 

Thanks in advance !

  • 0
    TI__Guru* 77501 points

    Hi Henkel,

    Leonard Henkel said:
    But for current smaller 5mA I’ve only got correct values for current in one direction. In the other direction the values are incorrect (and slowly falling).

    Here is a linear relationship for your bidirectional current sense. I see the opposite is true, when current is close to +/-50mA per your description. I reduced Rsen to 1ohm, see the attached file. 

    INA103 0-50mA Isense 09232024.TSC

    If you have other questions, please let me know. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 10 points

    Hey Raymond,

    thanks for the quick reply.
    I`m testing the INA in a test circuite which looks like this.

    In the simulation everything looks just fine.
    But in the real world I get the result I described. When applying small current like 2,6 mA in one direction I get the right output of -260mV. But if I change the direction of the current I get something around 1 V at the output.

    Best regards,


    Leonard

  • 0 in reply to Leonard Henkel
    TI__Guru* 77501 points

    Hi Leonard,

    Leonard Henkel said:
    When applying small current like 2,6 mA in one direction I get the right output of -260mV. But if I change the direction of the current I get something around 1 V at the output.

    In this +2.6mA direction, the INA113's circuit is working. 

    At -2.6mA, the circuit works as well. 

    INA103 0-50mA Isense Bidirectional 09232024.TSC

    The common mode voltage in both scenario across INA103 is closed to GND, and you are using dual supply rails. If INA103's input common mode voltage is different, then you may have issues - but it is not shown in your schematic. 

    You need to provide me more information what is the common mode input voltage when the current changed the direction. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 10 points

    Hi Raymond,

    I solved my Problem. It was caused by using Jumper for switching the direction of the current. I was only using them for one direction.

    Anyway. Thanks for your efforts.

    Best,

    Leonard