INA818: Device linearity differs from INA118

Sergio Reche Velasco

Part Number: INA818
Other Parts Discussed in Thread: INA118, TINA-TI, INA333, , ANALOG-ENGINEER-CALC

I am applying an instrumentation amplifier to a simple Wheatstone bridge with Vcm at 3V.
And single supply at 5V.
It turns out that in TINA-TI I get a perfectly linear output with the INA333 and INA118.
According to the INA118 datasheet, the INA818 is similar only by improving bandwidth and Vout range.
But I don't get the gain to be as linear as in the other INA.
Is it possible that the PSPICE model provided is wrong? What model should I use to simulate it?

Thank you very much.

over 5 years ago

0 Tamara M Alani over 5 years ago

TI__Genius 10850 points

Hi SrgiO,

Thank you for your post. I can help you. Can you share with me your TINA file? What is the expected input / output and gain?

-Tamara

0 Sergio Reche Velasco over 5 years ago in reply to Tamara M Alani

Intellectual 295 points

Thank you very much for your prompt response.
I attached the two circuits to measure increase / decrease in R4 and R11.
The original idea comes from TIDUB00-November 2015, in which using INA333 also works as with INA118.

Thanks again.
INA818_INA118_ReferenceDesign.TSC

0 Tamara M Alani over 5 years ago in reply to Sergio Reche Velasco

TI__Genius 10850 points

Hi SrgiO,

Ahh! I know what's wrong here. You are not operating the INA818 linearly. The INA118 and INA818 can not just be dropped in for one another without caution. The internal nodes of the INA818 differ from the INA118.

We have an online calculator called the Analog Engineer Calculator and within that is an INA Vout vs Vcm calculator where you can put in your supplies, gain, reference voltage and common-mode voltage to determine what is your allowable input / output range.

It looks like you set your common mode to 3V. The INA818 cannot allow this. If you set it to 2.5V, though, you will see better performance. Take a look at snippet of the calculator below. I will also attach the revised TINA file for you. INA818_INA118_ReferenceDesign-TA.TSC

-Tamara

0 Sergio Reche Velasco over 5 years ago in reply to Tamara M Alani

Intellectual 295 points

Wow!
Thank you very much, very effective!
Indeed, the problem seemed to be that from the beginning.

The fault is that I was using a version of INA-CMV-CALC that is different from the one included in ANALOG-ENGINEER-CALC and did not include the INA818. The one I downloaded is www.ti.com/.../sboc452 found at www.ti.com/.../INA-CMV-CALC. It may be necessary to update your page to match ANALOG-ENGINEER-CALC.

On the other hand I find that in the INA818 data sheet, www.ti.com/.../sbos894a.pdf on page 18, "Figure52. InputCommon-ModeVoltagevs OutputVoltage" also does not match the graph shown in ANALOG-ENGINEER-CALC. It is right?

I am very happy that you were able to give me a solution so quickly. I also love having the feeling of having learned something else.
Thank you!

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INA818: Device linearity differs from INA118