INA333 Gain Selection problem

Ganesh Singh Jayaram

Other Parts Discussed in Thread: INA333

Hi,

I connected the Resistor (1K SMD 1%) between the 1st and 8th pin of the INA333. Ref pin is connected to ground and supply voltage is +5 Volt and Ground. I suppose to get 100 times gain. but i am getting 2 times and it is non linear . like when i give 10mV input. output is 20mV. when i/p is 200mV o/p is 420mV.when i/p is 1.2V the o/p is 3.4V and when i/p is 1.5V the output is 5V. i am not able get any of gain except G=2 even after i changed the resistor from 1K to 100E. can any body help me to solve the problem?. My project is Related to PT100 temperature sensing.

over 13 years ago

0 Thomas Gulba over 13 years ago

TI__Intellectual 2770 points

Hi Ganesh,

It would be easier to find the issue if you also would post the schematic here. But: Did you provide a proper input bias current return path (see page 12 of the datasheet)? Did you do a TINA simulation? If yes: Did it work?

Hope this helps.

Thomas

0 Ganesh Singh Jayaram over 13 years ago in reply to Thomas Gulba

Prodigy 50 points

5554.PT100 3 wire.pdf

hi,

Mr.Thomas Gulba please find the schematics in PDF format. yet i didn't try TINA simulation.

0 Thomas Gulba over 13 years ago in reply to Ganesh Singh Jayaram

TI__Intellectual 2770 points

Hi Ganesh,

I'm pretty sure that you are violating the allowed input common mode range for the INA333. Figure 20 to 23 in the datasheet show this input common mode range more in detail.

You will also see a very similar behavior like you have seen in your measurements if you simulate the circuit with TINA. I have done a very basic simulation for, but you can download this free tool and the reference design and try it by yourself.

There are two solutions to your issue: Either move the supply voltages or move the input common mode range of the signal.

Hope this helps.

Amplifiers

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INA333 Gain Selection problem