Input voltage raíl to rail OpAmp higher than the power supply.

Eyyy guys!

I am wondering about the next issue. I want to use an opamp in the inverter configuration with a G=-0.5. This OpAmp is suplied with +-5v. And the input range voltage is:0-10v. Should it work without any problems? Or should I powered the OpAmp with +-12v to avoid stability problems?

Notice that I have been doing some simulations with ltspice and it looks working fine. But I am wondering about real life....

PS: the OpAmp which I want to use is the AD 8512. The input range voltage goes from -2v to 2v5 when is supplied with +-5v. However in my case I am having a gain of -0.5. So the maximum input voltage should be 5v. I think that it should not work...but I need some opinion

Thanks in advance

Guidelines for op amps state that input V should not exceed supply rails.

A resistive divider might be sufficient to reduce your 0-10V input range down to a suitable level.

The book of words says that with +/-5v supplies, the common mode input voltage range is -2.0v to +2.5v, its not stated anywhere in the specifications that it is a true rail to rail input op amp.

However.... FET op amps usually always have a common mode inputs right up to and slightly beyond the +ve supply, but suffer from phase reversal down near the negative supply rail.
This one has phase reversal protection.

So I would say you are o/k up to the positive rail, even though Analog Devices say not. It does not mention having any input clamping device or input protection.

If your +10 volt maximum comes from inside the same piece of equipment, its probably fine as the inverting input will not be driven up beyond +5v.

If that +10v comes from an external remote source, I would be placing a shottky diode between the inverting input and +5v rail to protect the op amp input.

Not sure why AD say the input common mode does not extend right up to the +ve supply rail. Maybe it does, but some aspect of performance degrades.

Hi,

An inverting Opamp solution with gain -0.5 will have both inputs to be 0V. So there will be no problem.
Don't mix the resistor voltages with the Opamp voltages.
Draw the schematic and see what voltages there are.

If you are in doubt show us your circuit.

Klaus