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THS4131 Vocm pin

Jay Heefner
Prodigy 20 points
Other Parts Discussed in Thread: THS4131

I have a design where I am using the THS4131 as a fully differential amplifier and in the process of getting it to production, the Vocm pin was left open. After reading the datasheet, it seems as though I should have tied it to circuit ground. I was wondering what the implications of leaving this pin open were. Does it just create a small offset on the outputs (not a problem for me), or can it affect other things like the noise performance of the part (could be a big problem)? I have not noticed anything strange or unexpected in the boards that have been produced this way, but I am wondering if I am just lucky.

Thank you,

Jay Heefner

  • 0
    TI__Expert 4950 points

    Jay,

     

    If you look in the THS4131 datasheet, figure 29, you can see that the Vocm pin is internally connected to either supply, so connecting it to gnd (ibelieve you are using it as a mid supply) is not necessary.  It is normally recommended to bypass the pin with a 0.1uF capacitor in order to limit the common-mode noise for that pin.  But since this is common-mode noise, as opposed to differential noise, it should not affect any of your performance.