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# INA326: How to compute for the Gain if there is no resistor R2?

Part Number: INA326
Other Parts Discussed in Thread: INA333

Hi Team,

Our customer is using INA326 with a single supply. He wants to connect Vref (Pin5) to V+/2 (BufferOP) so he doesn't have a resistor R2. He would like to know how to compute for the Gain.

Regards,

Danilo

• Hi Danilo,

He wants to connect Vref (Pin5) to V+/2 (BufferOP) so he doesn't have a resistor R2.

I think that this is what you meant. Gain = 2*(R2/R1), R2 is required. If Gain = 1, R2 = 0.5*R1 (both R1 and R2 here are referenced to INA326's datasheet notation).

Regarding the V+/2, two matching resistors are placed in series, has the thevinin resistance of R2||R6, shown in red marking ovals in the schematic below or R1 = 0.5*(R2||R6) or Gain = 2(100kΩ/40kΩ) = 5 V/V (resistor notations here refer to the Tina schematic below.).

The attached schematic simulation below has Gain=1.

INA326 Single Supply 07292021.TSC

Best,

Raymond

• Hi Raymond,

Thank you for your response. We have received further inquiries from our customer as follows,

in case of "FIGURE 5. Simplified Circuit Diagram" it isn't possible to connect a constant Ref-Voltage to Pin5,
because therfore vout is only working as an buffer!
Is there an alternative to INA326,
- where I can the Gain with only on resistor and
- the output is set to Vu/2 with an external reference Voltage?
- Vu 3,3V / VRef=1,65V / Gain ~ 20 / Iq < 2mA

Regards,

Danilo

• Hi Danilo,

The instrumentation amplifier options are per the requirements above.

For instance, with INA333, here is the circuit that will meet your requirements, but Vref=1.65V has to be a low impedance voltage source.

INA333 G20 07302021.TSC

With INA326, the same circuit looks like:

INA326 3p3V G20 07302021.TSC