ina114ap instrumentation amplifier

harsahib singh

Other Parts Discussed in Thread: INA114

I am working on ina114ap but i am facing problem in changing the gain ,no matter what Rg resistance value i use it constantly shows 2.9v for vin+ =5volt and vin-=0volt.

over 10 years ago

0 Pete%20Semig over 10 years ago

TI__Mastermind 25865 points

Hello harsahib,

It is likely that you're violating either the input common-mode voltage range or output voltage range of the device. Both of these ranges depend on a number of things, especially the supply voltage. Please read the following article series to understand these relationships.

www.edn.com/.../Instrumentation-amplifier-VCM-vs-VOUT-plots--Part-1
www.edn.com/.../Instrumentation-amplifier-VCM-vs--VOUT-plots--part-2
www.edn.com/.../Instrumentation-amplifier-VCM-vs--VOUT-plots--Part-3

0 harsahib singh over 10 years ago in reply to Pete%20Semig

Prodigy 45 points

Hi Pete,

First of all Thanks for your generous reply, I am describing the connections below please correct me where i am going wrong.

I am using 5v dc supply, and the connections are as follows : Vin+=5v,Vin-=-5v,V+=5v,V-=0V,Vref=0v and a 1k resistor across 1 and 8 terminals which according to datasheet provides G=50.I think all values are according to the datasheet,but still i am not able to figure out the problem.

0 Pete%20Semig over 10 years ago in reply to harsahib singh

TI__Mastermind 25865 points

Hello harsahib,

Sorry for the delay.

If I understand your connections correctly, you have a differential voltage of 10V and reference voltage of 0V. The equation for the output of the INA114 is:

Vout=Vdiff*Gain+Vref=((Vin+)-(Vin-))*Gain+Vref

With a gain of 50V/V the INA114 will try to output 500V (10V*50V/V=500V). Given a single 5V supply, this is not possible.

In addition, you are violating the input common-mode specification of the device as shown in the "Input common-mode range vs. Output Voltage" graph in the data sheet. I recommend reading the following series to understand this relationship:

http://www.edn.com/design/analog/4437848/2/Instrumentation-amplifier-VCM-vs-VOUT-plots--Part-1

http://www.edn.com/design/analog/4437922/Instrumentation-amplifier-VCM-vs--VOUT-plots--part-2

http://www.edn.com/design/analog/4438001/Instrumentation-amplifier-VCM-vs--VOUT-plots--Part-3

To understand how an instrumentation amplifier works, I would start by supplying it with dual supplies (+/-15V) and grounding the reference pin. Then set the gain to 1V/V by removing Rg. Then input a dc differential voltage (e.g. 1V) you should see 1V on the output. From there you can experiment by adding a reference voltage, changing the gain, etc.

I hope this helps.

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ina114ap instrumentation amplifier