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AIN0 in TM4C123GH6PZ loads when connected to output of TL084 Opamp

Hemant Kamat1
Intellectual 535 points
Other Parts Discussed in Thread: TL084, TM4C123GH6PZ

Hi,

I am using AIN0 and the ADC in the TM4C123GH6PZ to digitize a voltage between 0V and 3.3V. The analog input to the AIN0 comes from the output of a TL084 opamp circuit used in unity gain non-inverting buffer. There is a series 100 ohms resistance at the output of TL084 connecting to AIN0.

I noticed that after a short usage, the AIN0 pins loads the opamp output and the voltage input to the AIN0 almost halves.

Please advise on caution to exercise and prevent this.

Thanks for your time.

Regards,

Hemant

  • 0
    TI__Guru**** 244400 points

    Hello hemant

    Does the analog signal being measured have fast moving transient noises? If yes, then you would need a RC filter to remove the noise out of the signal. Since you have a 100 Ohms R already placed, might I suggest putting a C (100nF) mounted close to the AIN0 pin of TM4C123 device and then share the results.

    Regards

    Amit

  • 0 in reply to Amit Ashara
    Intellectual 535 points

    Hello Amit,

    Thanks for the response.

    I will get back to you once i have tried the solution.

    Regards,

    Hemant

  • 0 in reply to Hemant Kamat1
    Guru 47900 points

    As always - have you repeated this test upon multiple units - over some extended time-frame?

    Assumed is "normal" temperature and adequate powering (and decoupling) of both MCU & op-amp - is this the case?

    @Amit,

    Might a valuable test be this user's creation of an, "equivalent input circuit" to the MCU - and then connecting there - not to the MCU - and monitoring to see if the condition persists?  Such should narrow the list of "suspects."  If you agree - might you suggest optimum R & C values for the implementation of such an "equivalent input circuit?"  (equal to TM4C's ADC input)