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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

    If you have additional questions, please let me know. 

    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

    If you have additional questions, please let us know. 

    Best,

    Raymond