INA333: INA333 output is not coming as expected

Hari,

The minimum output voltage swing to negative rail is 50mV so it cannot go to 10mV you expect - see below.

Therefore, if you want to see 10mV at the output, you have to reference the output to a voltage at least 40mV above negative rail.  In the example below I used the 900mV input common-mode voltage as a reference voltage, and the output became as expected 910mV  (Vout=Vref+10mV).

Since the INA333 macro-model does not simulate voltage swing limitations as a function of gain, supply, reference and the input common-mode voltage, you need to download Instrumentation Amplifier Output vs Common-Mode Voltage calculator under following link:

Hi Marek,

"The minimum output voltage swing to negative rail is 50mV so it cannot go to 10mV you expect - see below." May I know Does this mean

the minimum possible output from INA333 is 50mV.

Thanks & Regards

Hari

Hari,

The minimum output voltage is 50mV above the negative rail. But remember that Vout=Vref+Vdif*Gain. Thus, with single 5V supply with Vref=0V, the output cannot be less than 50mV. However, if you use Vref=1V, Vout will correctly show 1.010V and if you use Vref=2V, Vout will correctly show 2.010V, etc.
Likewise, if you use dual supply, +/-2.5V, with Vref=0V, then Vout will correctly show 10mV because Vout would be 2.510 above the negative rail.

Hi Marek,

I made the changes according to your suugestion and circuit is working properly,thank you.

May I know how to see how much offest voltage is coming at the ouput of INA333 using TINA simulation.
If you can suggest some methods to cancel the offset voltage it is well and good.

Thanks&Regards
Hari

Hi Hari,

Which changes have you made? Did you move to dual supply or shift the reference? When you refer to offset voltage are you talking about the shift you have applied to the reference, or the actual offset voltage between the two input pins?

I would also recommend downloading the latest INA333 model as I noticed you are using an older version from 2011 and we have a newer version available in the tools and software tab. The newer version should accurately model the input/output limitations as well as the offset voltage so you can verify everything with simulation.

Hi Zak,

Thank you very much.
I moved to Dual Supply.
Offset I mean the actual offset between the two inputs.
I would like to do error budgeting for the above circuit(for self study).
I will download new model.

Regards
hari

Hari,

What are you targeting? The INA333 already has a very low offset voltage. Running in a gain of 4 you will see a worst case offset of 175uV at the output. The model is going to reflect typical datasheet values so you can use the datasheet limits if you need to do a worst case analysis.

Hi Zak ,
Thank you very much.
Once I finished my worst case analysis I will update you.
Regards
Hari