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# INA2332: INA2332: Output offset when diferential input is 0

Part Number: INA2332
Other Parts Discussed in Thread: INA2331, INA332, INA122, LM7705

I'm using a INA2332 for reading a diferential voltage from a bridge. When the diferential source is 0 (short-circuit), in the output I have 65mV, even when amplifier has no supply ( only with the diferential voltage connected).

Thank you!

• Hello User,

Can you please share the input common mode voltage, gain with resistor values, and supply voltages? If you can share with me the full INA schematic with values and connections, that would be helpful.

I simulated this on a 5V single supply in a gain equal to 10V/V. I applied a 0V differential and I got the expected output. Remember that on single supply, the input common mode voltage of the INA2332 can not swing to the negative rail, so you must boost this (typically this is boosted to mid-supply):

Vout = VREF + gain(V+ - V-) = 2.5 +10(0) = 2.5V

-Tamara

• Hi Tamara, thanks for reply. I don´t have the schematic drawn yet, but I can tell exactly the values.
Mi VREF is connected to ground, I set a gain of 21.12 V/V (R2=200k ; R1=62k) , with single supply of 5,5V. My common mode voltage range swings between 2,70V and 2,9V depending on each sensor.
When I have the differential voltage input in zero ( short circuit), I always have 60mV on the output (both channels), never rise the zero. That offset causes an increment of 100 counts on my ADC.
Then I realized about the 60dB CMRR of INA2332 (worst case for G=25), which means that the ratio between diferential gain an common-mode gain is 1000, therefore, the common-mode voltage gain is 0.021.
In that condition, the common- mode voltage output must be 2.70V x 0.021 = 57mV.
So finally, I think the low CMRR of this amplifier is generating a common mode voltage output , adding to the diferential mode output. Im looking for the INA2331(90 bB CMRR) to confirm this problem.

Do you think this reasoning is correct?

Thank you!

• Hi,

in section REFERENCE datasheet says: "The reference terminal defines the zero output voltage level."

So, from this statement it is already clear that an AC input signal will not work with Vref=0 in your circuit:

Not only that you are unable to reproduce the negative half waves of input signal, the output of INA332 even goes into saturation at 123.22mV (in your application 65mV, due to manufacturing tolerances). No OPAmp can fully reach the supply rails with it's output voltage.

So, you either run the INA332 with a bipolar supply voltage as shown in figure 1 of datasheet, or you provide a useful "zero output voltage level", here midsupply (2.75V):

By the way, do never apply the input signal when the supply voltage of INA332 is down. This might damage the INA332. See the ABSOLUTE MAXIMUM RATINGS of datasheet.

Kai

• Hi Kai, thanks for response. Im not using the amp for amplify waves. Im reading a DC voltage from a sensor. The typical swing from rail specified is 25mV. I have the same circuit on a INA122 and it works excelent, does no apreciate offset. How can I supress this 60 mV?

• Hi,

you could use the LM7705.

Kai