INA217 single supply

Hi Carla ,

I suspect you are having a common mode issue

Can you please share the schematic ,

Please ensure that the schematic includes the supply voltage , the common mode voltage and reference voltage clearly marked.

Regards

shreenidhi

Hi Shreenidhi,

First, when I made the following circuit, I did not get the gain from the datasheet, which was G=1 + (10k/RG).

I used a symmetric source made from a two channel voltage supply to provide the +5 and -5 V, and Ref and Vin-  connected to the virtual ground, as shown in the figure.

 

Is that right or a I made something wrong? If it's right, why didn't I get the gain equal to 2?

Second, for the Single Supply Voltage, I used the following circuit. 

Again, I used RG=10k ohms to make the gain be 2. And I used Vcc=5 V, the values from Vin wil be varying between 0 and 2 V, so I think I'm not going to have problem with saturation.

Thanks in advance,

Carla

hi Carla.

Thank you for the quick and elaborate reply

The 4th  sentence of the data sheet reads the device works from +/- 4.5 to +/- 18V

Hence for the device to used in single supply the V+ should be atleast equal to 9V

Thus the single supply case shown above is not possible as you have mentioned with INA217 as V+ is only 5V

The input common mode  range for the INA you have used is given below

 positive rail direction  = (V+)  -  4V

negative rail direction = (V-)    + 4V

The output limitation is given below

(V+) - 2 V

(V-) +2 V

Case 1

for a +/-5 V supply as you have mentioned in case 1 , 

for the output to be linear with respect to your input  , the output needs to be between  -3V  to +3V only

And your input needs to be -1V to +1V only

 

As you are supplying a signal of 0  to 2 V with a gain of 2 ,

your are violating both the conditions (input and output)

Hence you are not able to get a linear relation between input and output which is making it appear like your gain is not equal to 2

Case 2

for a +5 V and GND  supply as you have mentioned in case 2 , 

for the output to be linear with respect to your input  , the output needs to be between  +2  to +3V only

and the input common mode range is violated in all cases

Hence device cannot be used with a +5V single supply as mentioned earlier

hence i would recommend using a INA in which the common mode voltage range is not violated and output is also within the specified range

Also you can tweak your inputs as shown below to make sure you are not violating the input common mode range

 

Regards

Shreenidhi  

 

 

I'm sorry but I didn't get the values that you mentioned for the input and output range in all cases.

In my understanding, in case 1, if I use +-5 V supply, I expect a maximum output voltage range of +-5 V, but you said that it needs to be between -3 to 3 V. Could you please show me how you found those values? And also, I don't understand the limitation on the input values.

Sorry, I'm a beginner :)

Hello Shreenidhi,

I watched the video and I fully understand what was going on with my circuit! Thank you so much for you help (and the video that is super detailed!)

However, I took a look at another component's datasheet - http://www.ti.com/lit/ds/symlink/opa2137.pdf  - and I don't have a max value for Common-mode voltage range.. I have only (V+)... does that mean any default range or something like that? 

Thank you again!!!! Sorry for being detouring the post.

Hi carla,
No problem, we are always glad to help you

So the datasheet of opa2137 mentions common mode input stage as( V-)+3 V to V+

V+ here means the vcc or the positive supply you have connected to the op amp

For example
If say op amp is connected to +/-10V

The input common mode range is - 7 to +10 volts

Regards
Shreenidhi

Thank you so much!

Regards

Carla