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From reading some threads here I understand that the Common Mode Voltage of a Current Sensor Amplifier when measuring high-side is the average of the positive and negative input pin.

In my application I would like to measure the current in both directions. If I - as a bad example - say I select a INAx180 and look at the common mode voltage it says:

Recommended VCM:         -0.2V to +26V
Absolute Maximum VCM: GND-0.3V to +26V

Am I correct to assume that I could measure a current where the positive voltage input (IN+) is greater than the negative voltage input (IN-) but would be unable to measure a current in the other direction (if it exceeds the -0.2V difference)?

Tom L.
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    Tom, it seems I've misread the data sheet: @AndyAka is correct and I can only upvote his own answer below, and Just point our that if you need a bidirectional current monitor, perhaps it is better to use the INAx81 which gives accessibility to the reference pin of the differential amplifier in order to set its value to half of the power supply voltage. – Daniele Tampieri Jul 10 '23 at 12:41
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    Thank you for clarifying, Daniele. – Tom L. Jul 10 '23 at 20:17

1 Answers1

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In my application I would like to measure the current in both directions.

It can't fulfil that functionality. The data sheet says this: -

enter image description here

This means that for high-side sensing, the inverting input has to be no greater than the non-inverting input and, unfortunately, with a "reverse" current flow would contravene the data sheet.

Common Mode Voltage on Current Sense Amplifier (direction of current)

It's got nothing to do with input common mode voltage; it's a simple case of the amplifier not being able to produce a negative voltage on its output should the input pins be "role reversed".

Andy aka
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  • Thank you for responding. Apparently I was looking and interpreting the VCM wrong. Is there any place in the electrical specification where I would see that information except for the text? I understand that if the current got "negative" it would need to output a negative voltage and not having a negative voltage supply this would be an issue. I saw that there are bidirectional current sense amplifiers (e.g. the INA241x) where the reference input is set to some mid value (zero current point?). Considering the other specifications are ok, those should work I guess? – Tom L. Jul 10 '23 at 11:35
  • @TomL. it looks like the INA241x will work because the internal op-amp biases the output to mid-rail. As to where you might see it, for an op-amp veteran, it's clear from the picture on page 1. – Andy aka Jul 10 '23 at 11:40
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    That's what I feared :-) Once oyu have the experience it's crystal clear. If you don't .. well .. I understand the implications now but it took a while to come that far. – Tom L. Jul 10 '23 at 20:16