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INA121: Using singles supply (12 V to generate output signal from ~ 2 V to 10 V DC - not working - wrong chip (except overkill?)

Wolfram Neff
Prodigy 20 points
Other Parts Discussed in Thread: INA121, OPA171

Hello, 

I have a very simple problem - I need to amplify a DC output of an Arduino Due to 10 V  (using the true 12 bit DAC output). 

I use an INA121 in single supply voltage (12 V), have the Ref and V- and the inverted input to ground and feed 2.5 V into the "+". 

Getting 1.5 V out.  Is this the correct circuit or do I need to give it a 6 V reference for the chip to think its really at +/- 6 V? 

...or is it really not a DC amplifier????

  • 0
    TI__Genius 12325 points

    Hello,

    The INA121 is absolutely a DC amplifier, however the device will not work properly with the negative supply, inverting input, and reference pin all tied to ground. The device was really designed for bipolar supplies(+/-12V). In your application though, an instrumentation amplifier may not be required. What is the DAC output voltage range? 0 to 2.5V? A single op amp with a rail-to-rail output, and input common mode range that includes the negative rail (such as the OPA171) should be able to accomplish this. 

  • 0 in reply to John Caldwell
    Prodigy 20 points

    Hello,

    thanks for the feedback - the DAC output is 0.55 to 2.75 V, so we don't even need to go to 0. I was loking for small long-term drift and thats why i picked the INA121, and the spec sheet mentiones it can be run form a single 4.5 V battery.....

    I am gong to try the OPA171 - is there a 2 channelversion? In 8 pin dip package?

    Thanks