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INA129 - single supply at +5V and GND?

Other Parts Discussed in Thread: INA129, INA326, INA188, INA333, TINA-TIPart Number: INA129

Question type: Development and troubleshooting

Support topic: /Product/Development and troubleshooting/Help with board layout or design considerations/

Description of the problem: Am I able to use the part, INA129, powered with a single supply at +5V and GND?

  • Hello Peter,

    You can use the INA129 with a single 5V supply, but please understand that the linear operating region (Vcm vs. Vout) will be very limited due to the internal amplifiers' common-mode and output swing limitations. I recommend reading the articles in the following FAQ and downloading the Vcm vs. Vout calculator.

    Vcm vs. Vout FAQ:

    https://e2e.ti.com/support/amplifiers/precision_amplifiers/w/design_notes/3373.understanding-instrumentation-amplifier-vcm-vs-vout-plots

    INA Common-mode Calculator download:

    http://www.ti.com/tool/ina-cmv-calc

    An alternate part that you may consider is the INA326.  The INA326 has a unique topology that enables RRI/O operation.

  • I used the Vcm calculator and it looks like at +5Vin and gain of 1 V/V, Vout and Vin will only be linear from 1.87V max to 0.8V min with a common mode voltage of 2.66V.  I'm a little confused about why the CM voltage  bar only lets me go from 2.13V to 3.2V.  Why can't I set the CM to 0V?

    I think INA188 might be a better option.  The datasheet specifically says it can operate with a single supply and goes rail to rail.

     

  • Hello Peter,

    You can set the Vcm to 0V, but you'll be violating the linear operating region of the device. Please read the articles in the FAQ...especially the first 3 which discuss 3 op amp instrumentation amplifiers. The INA188 is also a 3 op amp instrumentation amplifier so it's linear operating region will also look like a triangle when operated single supply with Vref=0. The maximum output swing will be from 220mV to ~3.3V when Vcm=~1.86V.

    Hope this helps!
  • The INA common-mode calculator does not have INA326 part loaded.  Is it because it's  RR I/O and therefore doesn't have a plot?

    I did a simulation in Tina with the INA326 in the circuit I plan to use and it behaves like I expected.  But I also did the simulation using the INA333 instead, and it works the same.  Vcm is 0V.  Vdiff is less than 1V. V+ is +5V, V- is GND, and Gain = 1, Ref = 0.  

  • Hello Peter,

    Yes, the INA326 has a special topology that allows for RRI/O. Therefore it does not conform to the same limitations as traditional instrumentation amplifiers. Please note that TINA-TI models do not necessarily model Vcm vs. Vout limitations...that is why we created the common-mode calculator.