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TLC2652 inverting DC, large noise at V-

zhen zhang2
Intellectual 370 points
Other Parts Discussed in Thread: TLC2652, OPA170, OPA333, OPA188

Hi Everyone,

I am trying to use TLC2652 in inverting unity gain configuration to invert my DAC DC output.

I followed the below schematic for my design. additionally,  placed a 0.1uF cap crossed R2.

The issue is that I am getting a large noise a V- ( around 50mVpp), 

Therefore, The output is a very noisy. I am not sure where is this noise coming from, The input is very stable. (My input is 1V from DAC.)

i am suspecting that i am not configuring the op amp correctly. The data sheet suggested 2 caps at CxB and CxA Pin. I put 0.1uF cap from CxB/A to Vdd- each.

Please help to see What could i  be doing wrong?

Thanks a lot for your help,

Eddy

  • 0
    TI__Guru 62745 points
    Hi Eddy,

    Are you using the TLC2652 or the OPA170 in your application? The title mentions the TLC2652 but the schematic you've drawn shows the OPA170.

    The TLC2652 is an older chopper amplifier and you will see more evidence of the chopping than you would with a newer chopper amplifier such as the OPA333 or OPA188. The nominal chopping frequency for the TLC2652 is 450Hz. Is this around the frequency you see the noise at? Make sure you have a capacitor on each of the Cxa and Cxb pins to the V- supply. Be sure to use good quality X7R or preferably C0G / NP0 capacitors for best performance.
  • 0 in reply to Collin Wells
    Intellectual 370 points
    Hi Collin,

    I tried a different Op amp(OPA333). I do not see that problem anymore .

    Thanks,
    Eddy