LMV331 Input Voltage Range (V_CM)

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on Apr 17 2012 07:52 AM

I am looking to clarify the meaning of the parameter V_CM, Input Voltage Range, from page 3 on the LMV331 datasheet. This value is listed as -0.1V to 4.2V given a VCC of 5V, I am trying to verify if this relates to an absolute maximum for the inputs to the part or if it relates to the common mode input.

The input common mode voltage for an op-amp is (V_IN+ + V_IN-)/2, the name of the parameter implies an absolute range, but letters in the symbol, V_CM, implies this parameter relates to Voltage Common Mode.

With VCC=5V and one input being 4.5V and the other input being 2V will this violate the V_CM parameter for this component?

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Posted by Paul Grohe

on Apr 17 2012 10:53 AM

Verified Answer

Verified by Zachary Glickstein

Expert4295 points

HI Zachary,

The common mode limit is an absolute for each pin, not the average of the two pins. The formula is correct, but not applicable...

Comparators can have differential voltages of several volts, so one input does not get a "free-pass" because the other input is at a much lower voltage.

A VCM limit of 4.2V means do not go above 4.2V....

So, yes, if one input is at 4.5V, you are violating the VCM specification, regardless of what is on the other input.

You will need a R-R input device like the LMC7215 or TLV3401.

Regards,

Paul Grohe

Integrated Signal Chain Applications, SVA

Posted by Zachary Glickstein

on Apr 17 2012 16:51 PM

Prodigy50 points

Thanks, this ansewers my question.

Posted by Ron Michallick

on Apr 18 2012 11:42 AM

Verified Answer

Verified by Ron Michallick

Mastermind30440 points

Zachary,

The LMV331 only needs one input to be in the common mode range to have a valid output.
If both inputs are above the maximum common mode range or either input is below ground then the output is undefined.
Neither input should exceed VCC.

Your example voltages will provide a good output.

Regards,
Ron

Regards,
Ronald Michallick
Linear Applications

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