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# What is the Common mode voltage range of ADA4522-2 ?

Hi,

I would like to know the common mode voltage range of ADA4522-2. I am using this as a buffer. The supply voltage to the Op-Amp is ±5 V and my input would be near to 5V( assume 4.9V). What can be my possible output value.?

• Hi Emman,

Thanks for the information.

• Hi Ashok,

What datasheet are you referring to? Single supply operation means that one supply pin is connected to ground but it doesn't imply the input voltage range that it is capable to accept. You need to always check and refer to its datasheet regarding the input and output voltage range for you not to violate any conditions for that particular amplifier.

Best regards,

Emman

• Hi Emman and Harry,

Sorry to bring up this question again.

When i was going through the datasheet i saw something called Single supply Operation.. !! What does this actually mean?

If its showing 5V single supply operation, does it mean that I can apply ±5V across V+ and V- ?? Or its just 5V and ground across V+ and V-.

Ashok.

• Hi Emman,

Actually I understand that there are some limitations for the IVR as you said in your previous replies. I wanted to know about single supply operation whether its between ground or not. You have answered that.

Regards,

Ashok

Before 1975, most op amps ran on +/-15V, and the IVR was +/-12V, or +/-10V or whatever.

So if you ran it on ground and +30V, the IVR was 3V to 27V.  National invented the LM324,

which had a PNP input stage, so if you ran it on ground and +5V, the IVR was ground to 3.5V.

So the official definition of single supply is an op amp where the IVR includes the V- rail.

Having said that, all op amps will run on a single supply, but you have to watch out for the IVR.

Harry

• Hi Emman and Harry,

I was currently doing the testing of the constant current source when i came across a problem which i am not able to figure out why it is happening. Please help me out.

Problem:

In a buffer circuit the input voltage is measured across a 120k resistor. The opamp used is ADA4522-2.

Case 1:- When a single DMM is used to measure the input voltage, a particular value specific to the current flowing is obtained. When the same DMM is used to measure the output voltage a difference of 20mV from the input voltage is obtained.

Case 2 :-  When i use 2 multimeters simultaneously for the measuring the input voltage and the output voltage with their respective negative probes connected to ground, the difference in the multimeter readings has been drastically reduced to less than 0.1mV. In fact when both of them are placed simultaneously, the output voltage(which had a 20mV difference is getting automatically reduced to the same value as the input)

What may be the reason behind this? Why was the buffer giving a difference in input and output at the first case?

Regards,

Ashok

• For case 1, is the output voltage higher or lower??  (I'm guessing higher)

What is the input impedance of your meter?

Have you tried a different brand of meter?

What is the source impedance of the node you are measuring?

Harry

• Harry,

Yes, The output voltage is higher.

The input impedance of the meter is 1MOhms.

I tried with a different brand. In-fact the values both of them showing are almost same.. with some mV difference.

I am probing on the non-inverting input pin and Output pin of AD8639 opamp.

As per the datasheet of AD8639, the input resistance is given as 22.5Tohm and closed loop output impedance is given as 4.2Ohms.

Ashok.

• Hi Harry,

My system is functioning well.. I increased the input impedance of the multimeter and now i am getting the input and output values of the buffer very close to each other.

Regards,

Ashok

• Don't know what your schematic is, but if you have a current source driving a 120k resistor,

and you put a 1Meg DVM across the 120k, the current source has a high output impedance

and supplies a fixed current, so some of the current goes through the 1Meg and you get a

lower voltage across the 120k.

Harry