AD8274 -- how is common-mode voltage defined?

Looking at the specs, in particular figures 8 and 10 on page 6, the common-mode voltage seems to be limited to 25V for +/-15V supplies.

My question is:  where is that 25V measured?  At the pins of the IC, or at the inverting and non-inverting input pins of the op-amp?  If the former (which seems reasonable, since the specs are given for the IC), then I cannot understand why if I use it in a gain=1/2 configuration, with +/-15V supplies, the circuit would fail with two identical input voltages of 30V  (the voltage at the input pins of the op-amp would be 10V, which is within the power supplies range).

Can you confirm?  (or clarify if there is something I'm misunderstanding?)

Thanks,

Carlos

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  • 0
    •  Analog Employees 
    on Sep 21, 2017 1:02 AM

    Hi Carlos, 

    I apologize for the confusion, I meant 30V as supply, not common-mode. If you will be using the AD8274 in a single supply, you can scale up the diamond plot. See below:

    So for a 30V supply, with a 28V input common-mode level, the output swing would be somewhere around 5 to 25V.

    We do have current sense amplifiers, which are designed to be used in these exact applications where high common-mode levels are expected. You could check out the AD8418 if it suits your purpose. 

    Thanks, 

    Kris

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  • 0
    •  Analog Employees 
    on Sep 21, 2017 1:02 AM

    Hi Carlos, 

    I apologize for the confusion, I meant 30V as supply, not common-mode. If you will be using the AD8274 in a single supply, you can scale up the diamond plot. See below:

    So for a 30V supply, with a 28V input common-mode level, the output swing would be somewhere around 5 to 25V.

    We do have current sense amplifiers, which are designed to be used in these exact applications where high common-mode levels are expected. You could check out the AD8418 if it suits your purpose. 

    Thanks, 

    Kris

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