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DAC60096: Doubling DAC output with OpAmp

Mal Hubert
Prodigy 10 points
Part Number: DAC60096

I want to use an LM358N Dual OpAmp to double the range of each (pair) of outputs of the DAC60096.

I have the DAC outputting -10V to +10V driving using the SPI bus no problem.

I am trying to use an OpAmp to do the non-inverting voltage double, but getting nothing out (Vout to AGND). Here is my setup. I would appreciate some thoughts on where I have gone wrong, because I'm sure it's wrong !

I had an OpAmp on its own doubling a 5V to 10V, but it won't double the DAC output.

  • 0
    TI__Mastermind 28058 points

    Hi Mai, 

    When you connect the DAC output to the op amp, do you still see the 0-10V output on the DAC output when you change the code via SPI?

    And just to double check, are you using the DAC output in the negative range at all? Even potentially on startup? I don't see a negative supply on the op amp so this could damage the op amp if you are every connecting the input to a negative voltage. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Prodigy 10 points

    Yes I do see the correct output from the DAC. It does output in the negative range as well. I don't initially want to use the negative range, but thanks for the note, I will need that negative supply as well if I do.

    Is AGND correct to connect to the OpAmp in this case ? This is the bit I'm not sure about.

    I can get the OpAmp on it's own to double the input voltage, but not from the DAC, it's the act of integrating the 2 which is not working, hence I'm suspicious of what GND I should be using.

  • 0 in reply to Mal Hubert
    Prodigy 10 points

    R1 and R2 are actually both 1K

  • 0 in reply to Mal Hubert
    TI__Mastermind 28058 points

    Hi Mal, 

    When the DAC output is connected to the op amp, are you ever using the negative range? This could be damaging the op amp because you don't have a negative supply. It is correct to connect AGND to the op amp, but when you do this you should never configure the DAC for a negative output. 

    When you have the two devices connected do you see the correct DAC output voltage? I mean when you measure the highlighted node while the two are connected:

    Best,

    Katlynne Jones