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ADC12DL040: ADC Amplifier Exhibiting Incorrect Behavior

William Kalfus
Prodigy 30 points
Part Number: ADC12DL040

I am designing a system that incorporates the ADC12DL040 ADC. Page 27 of the datasheet gives the following example schematic for converting a single-ended signal into a 1V +/- 0.5V differential signal as required by the inputs to the ADC: 

With the following table for the values of the unspecified resistors: 

My signal input ranges from 0-0.5V, so I used the resistor values in the second row. I am trying to simulate the amp in LTspice with the following schematic: 

However, simulating a 0-0.5V linear DC sweep produces the following output, rather than two 1V +/- 0.5V signals: 

Any idea where the circuit is going wrong? Thanks!

  • 0
    TI__Mastermind 44680 points

    Hi William

    We are looking into the issue.

    Someone will respond with more information as soon as possible.

    Best regards,

    Jim B

  • 0
    TI__Genius 12780 points

    Hi William,

    I used Tina ()  to simulate the circuit. Here is the file I used  AnalogInput_0to0.5V.TSC.

    Looking at the circuit, you can see that I tied the DC voltage that is feeding into the non-inverting input of OP4 into the non-inverting input of OP3. This way, both inputs will share the DC offset (common-mode) of 1V and are 180 degrees out of phase (90 and -90). Also, you will notice that the amplitude of the output at both VIN+ and VIN- is 1V. This meets the requirements in the data sheet (Seen below) of 1V +/-0.5V.

    Is this what you were looking for?

    Regards,

    Dan

  • 0 in reply to dBrock
    Prodigy 30 points

    This does resolve what I was looking for. Your resistor values are also different from what the datasheet recommends, as expected. Hopefully the datasheet can be updated to fix this issue.