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PGA280

Matthew Odinotski
Prodigy 120 points
Other Parts Discussed in Thread: PGA280, PGA281, TINA-TI

I have a board with a PGA280.  The Analog supply is connected to +/-12V, VSop = 5V, DVdd = 3.3V.

I'm currently using the power on Reset values for all the settings (1/8V, 1:1, etc).

InN1 is connected to GND

InP1 is connected to a signal source (100hz, -5V to 5V sinewave)

Vocm = 2.048V

What I don't understand is why the outputs: Vop = (100hz sinewave from 2.1v to 2.775V) and Von = (inverted sineware from 2v to 1.32V).

Shouldn't these signals be centered around Vocm (or 2.048V)? and the sinewave crossing over the Vocm level?

What am I missing here?

thanks in advance for your help

Matthew

  • 0
    TI__Guru 63225 points

    Hello Matthew,

    Would you please post a scope shot of the input and output waveforms for us to take a look at?

    Also, are any of the error indicators displaying an error?

  • 0 in reply to Collin Wells
    TI__Mastermind 27715 points

    Hello Matthew,

    Based on your description, you should be seeing an output voltage centered around your Vocm input of 2.048V. However, without a circuit schematic or input/output waveforms available I cannot confirm this.

    One step I recommend is downloading the TINA-TI reference simulation circuit for the PGA281 from the following link: http://www.ti.com/lit/tsc/sbom817

    The PGA281 contains the same analog core as the PGA280 and can be used for debugging analog behavior. Modify this reference circuit in TINA-TI (our free SPICE simulator) using your circuit configuration and see if you can duplicate the issue. 

    Best regards,

    Ian Williams
    Linear Applications Engineer
    Precision Analog - Op Amps

  • 0 in reply to Collin Wells
    Prodigy 120 points

    Hi Collin,

    No error indicators.  After struggling with this for a few days, I just decided to replace the chip on the board, and everything started working.  Maybe I stressed out the chip while testing the front end of the pga.

    Thanks for your help

    Matthew

  • 0 in reply to Ian Williams
    Prodigy 120 points

    Hi Ian,

    I had the chip replaced this afternoon, and it seems to have resolved the issue.  I was  working on the front end circuit, and maybe I stressed out the pga.  I'll let you know if it happens again.

    thanks for the suggestions

    Matthew

  • 0 in reply to Matthew Odinotski
    TI__Mastermind 27715 points

    Hi Matthew,

    Thank you for the update. Please let us know if you experience any more unexpected behavior while evaluating the PGA280.

    Best regards,

    Ian Williams