Instrumantation amplifier datasheet reading help

dark said:

Hello Forum,

I need to interface LT1101 LTC IA for a circuit. I power the IA with 12V single powersupply. However after reading the datasheet I couldnt get a clue as to what CMV can the IA input pins could handel . The amplifier datasheet is here ; Linear Technology - LT1101 - Precision, Micropower, Single Supply Instrumentation Amplifier (Fixed Gain = 10 or 100)


Thanks in Advance
-D

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dark said:

Hi,

Thanks for the replies . I know these specs , but as I power only from 12VDC and 0V as said in my first reply. I cannot makeout a spec for this ,all the details given are related to either 5V or +/-15V . But what about if we use a 12V powersupply?

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ericgibbs said:

hi,
If you extrapolate the limits for the 5V supply and the dual, it gives a value of approx +Vss-2v and 0V + 0.7v
Look at the 3rd image graph I posted for a dual
So I would expect for a 12V supply a CMV range of approx +10V and +0.7V.
Can you post a circuit or some details of what you are trying to do.?

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dark said:

Hi,
Thanks that is helpful . I dont have a circuit yet but only analyzing the possiblity. I am getting a diferential signal from a force sensor which shows a common mode signal of 5.5V and more.


The above image further explanes it . Does minimum CMV vs O/P voltage means that it can sustain an 'x' output while having 'y' as CMV at its input?

I have a further concern datasheet quotes
"In single supply applications, both input and output voltages swing to within a few millivolts of ground" here shall we take a factor of 180mV to remain in the safe limits .

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ericgibbs said:

hi,
I have marked the graph for CMV versus output voltage at G=100 and G1=10
With a CMV of approx 5.5V and a 12V supply you are well within the CMV range and the amplifier should work OK.
With respect to the output swing, its dependent upon the output load.
If the lower output limit is required to work to a 0V level, then a dual supply is required.

Whats the output of the amplifier connected to.?

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