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INA500: VREF and V- Tied to Ground (positive only configuration)

Keith Keller
Expert 6690 points
Part Number: INA500
Other Parts Discussed in Thread: TINA-TI

Hello,

We are designing with using the INA500A difference amplifier.

Planning to put only positive input voltage (i.e. Vin+ > Vin-) on the input pins of the INA500 and we expect only a positive output voltage, so we would like the REF pin to be tied to GND.

According to the application section of the datasheet, the INA500 can have the REF pin tied to GND, as shown in Figure 8-2.

Please note that Electrical Characteristics Table (Section 6.5) shows the following linear input voltage range for the INA500A’s reference pin voltage:

Please note the (V-) + 0.1 minimum value stated here. The V- in our application will be tied to GND.

  • How might the performance degrade if we do this?
  • Does CMRR increase?
  • Does gain accuracy change?

Thank you, Keith

  • 0
    TI__Genius 11326 points

    Hi Keith,

    Great question. The datasheet is specified this way to ensure the amplifier output is not saturated with 0V input. 

    If we ground the ref pin and have 0V across the input terminals, the amplifier will try to drive to 0V: saturating the output at the VOL voltage of the part:

    Therefore, grounded VREF operation is perfectly fine, the only consequence is that it will not be possible to linearly amplify any signal which requires voltages less than VOL to be output from the amplifier.

    Here is a TINA-TI simulation that shows that INA500 will not output all the way down to 0V with grounded Vref. Input (Red), Output (Green)

    CMRR will get worse if the output clips like previously mentioned. Otherwise CMRR will be unaffected.

    Gain accuracy does not change unless the output clips. 

    Please let me know if you have any other questions.

    Best,

    Jacob