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ISO122JP problem

Haim Lib
Intellectual 360 points


Hi

I am trying to use ISO122JP with supply of Vs1 = +/- 15V and Vs2 = +/- 15V . Input signal range from 0 to 10V . Problem the big output error . For 8V input signal  I am getting 13 V output . ????????????

  • 0
    TI__Guru* 93105 points

    Hi Hiam,

    The ISO122JP should be able to provide an 8 V output with an 8 V input providing:

    • The device is connected correctly, with correct component selections. Can you share your circuit schematic?
    • The device is a genuine TI ISO122JP. Did you obtain the device via the TI distribution channels?
    • The device wasn't ESD damaged during handling.

    An output voltage level of 13 V could indicate the output amplifier section is up against its positive output swing limit. Does the output level move off 13 V when the input voltage is reduced?

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Intellectual 360 points

     

    Thank you for support

    1. Attached  schematic
    2. Output voltage level between 5V and 13V depend on Input
    3. Component came from Digikey
    4. ESD damage ( I don't know)

     

     

     

     

     

     

     

  • 0 in reply to Haim Lib
    TI__Guru* 93105 points

    Hi Hiam,

    Your implementation of the ISO122J is straightforward and I don't find any problems with its portion of the circuit schematic. The problem you are chasing is one as if the circuit is operating with a gain greater than 1 V/V, producing a higher output voltage than expected for a given input voltage.

    When you observe this unexpectedly high output voltage are you monitoring the output of the ISO122J, test point P141, or the AMP OUT point? If the output voltage at P141 is too high, then the ISO122J is suspect and you should try a different device in its place. If the output voltage is okay at P141 and too high at AMP OUT, then something is not working correctly in the OP77 circuit. Its gain should be 1 V/V within its pass-band.

    Re-check your supply voltages on ISO122J power supply pins and also the OP77. You might want to do so with a DSO. That way you can observe the input signal at the ISO122J input, output, power supply lines, and OP77 output. Make sure you are not seeing any oscillation, or anything else unexpected.

    Regards, Thomas

    PA - Linear Applications Engineering