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ADS8505: ads8505 output variation problem

Hitesh Majethia
Prodigy 10 points
Part Number: ADS8505

Hi,

This is Hitesh, I am using ADS8505 for data aquistion purpose.

I have output votlage variation problem in my boards.

say if we give 2.5V DC as input. the output will varying from 2.491 to 2.507.

the above is fact after applying a averaging ( 10 times).

I am also attaching the pdf of the ADC schematic.

Please help to solve the above problem.

Thanks,

HiteshADC SCH.pdf

  • 0
    TI__Mastermind 24388 points
    Hitesh,

    We will look into this and get back with you soon.

    Art
  • 0 in reply to Art Kay
    TI__Genius 16890 points

    Hello Hitesh,

    Here are some troubleshooting steps to determine where the problem is coming from.

    Remove R35, R34 and disconnect the input from pin 1.

    Apply a stable 2.5V to the input.  Note this has to be a good supply, if it varies or has noise this test is invalid.  This setup is using the internal reference and along with the low noise, stable input will show if the problem is with the ADC or the external parts.  If the results from the ADC are stable then the ADC is ok and the problem is from the external circuit.

    Install R35 and adjust R69 so that 2.5V is at the reference pin.  If the output values now become unstable the problem is in this part of the circuit. 

    Connect the output of the op amp to the ADC input.  If the output values now become unstable the problem is in this part of the circuit. 

    Install R34.  If the output values now become unstable the problem is in this part of the circuit.

    Mike