Need help understanding a value in a datasheet

[mattisafur]

Hi everyone,

I'm making a crude high voltage diff probe using an INA217 instrumentation amp.
I'm having an issue understanding it's supply voltage from it's datasheet:

(Maximum)


(Recommended)


I can't figure out if they're meaning (+-)15V between it's supply rails or between each one and ground.

I've tried checking TI's pdf on reading opamp specs but couldn't find an explanation on supply voltages. I also tried checking forum posts for similar questions but found nothing.

does anyone know how to read suck supply voltages?

Best regards,
Matt.

[jpanhalt]

Each rail and ground.

EDIT: Do a thought experiment.  Assume you attach your voltmeter correctly and measure only between each rail.  You see +30V.  How would you know was as +15 and the other -15?  They could be, for example, +25 and -5 or +30 and 0.

[mattisafur]

Thank you!

How would you know was as +15 and the other -15?  They could be, for example, +25 and -5 or +30 and 0

That's a good point! I'll try thinking about scenarios like this one next time I won't understand some part of a datasheet.

[Terry Bites]

They are specifying minimum and absolute maximum for the supply rails eg 9 volts to 36 Volts total. Often referred to as supply span.
So they are saying -4.5 0 +4.5  to -18 0 +18. Its not a good idea to run at the absolute max supply.
Of course it doens't necessarily have to be centred around 0V, you could run from +5 and -9 if you like. Check your Vout vs Vcm plot to make sure the inst amp is inside its working range.

[rstofer]

A couple of things to be aware of:  First, notice the limit on input voltages, 0.5V below the lower rail and 0.5V above the upper rail.  Don't work outside these boundaries.  Those are the MAX limits, there may be other restrictions that won't destroy the device but it might not give the proper output.

Second, your datasheet screenshot doesn't show it but the datasheet should tell you how close to the rails the output can swing.  In the good old days, a system with +- 15V rails might work over a range of +-10V for inputs and outputs.

There will also be a limit on how close the inputs can swing toward the rails.

See around 10:00 here:

Here is a paper on 'phase reversal' where the output does weird stuff at various input levels:
https://www.analog.com/media/en/training-seminars/tutorials/MT-036.pdf

Dave has some good op amp videos as does w2aew

[Jay_Diddy_B]

Hi,

There is a typo on the INA217 datasheet:



The difference between V+ and V- should always be positive. That is V+ more positive than V-.

They show the difference as +/-, which is wrong.

regards,

Jay_Diddy_B