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OPA827: midsupply, VCM, VOUT

Part Number: OPA827

Hi officer,

I am just writing to enquire about 1 thing on the datasheet of opa827. Please see the highlighted part in the picture above. What is 'midsuppy', can I interpret it at the middle voltage level of +VS and -VS, in this case 0V?

And may I ask the meaning of 'VCM = VOUT = midsupply'?

Is this the initial test condition?

Is there any test circuit?

thanks,

Jim.

  • Morning Jim,

    That is just one way to handle single supply or balanced bipolar supply conditions. So if you are say +/-15V, that Vcm is 0V.If you are single 18V, that Vcm is 9V. Just trying to condition the spec table to be assuming the output is centered on the supplies.

  • Hi Michael,

    Thanks for your reply.

    Let's say VS+ = 18V and VS- = -18V. -> Midsupply = 0V. 

    Why is Vout = Midsupply = 0V? Is that Vout got when there is no input?

    thanks,

    Jim.

  • Hi Jim,

    Yes, with +/-18 V supplies half way between that total 36 V span is 0 V. This condition is mid-supply, or the mid-point between +18 V and -18 V.

    Assuming the OPA827 is set up in a closed-loop gain with the non-inverting input at mid supply (0 V), the output voltage would ideally be 0 V too. However, due to the Op amp internal, no-ideal characteristics that contribute to voltage-offset, the output will be slightly off of 0 V by Voso = Vosi (1+Rf/Ri).

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • Hi Thomas,

    thanks for your help!

    BR,

    Jim.