INA125: Recommendation for current excitation bridge pressure sensor

Part Number: INA125
Other Parts Discussed in Thread: INA333, LM234, OPA388, OPA387

Tool/software:

I  request your recommendation for an instrumentation amplifier suitable for use with a high-pressure sensor (part number: NPI-15B-352ah) that requires constant current excitation.

The specific requirements for the sensor are as follows:

  • Input Excitation: 1.0 mA
  • Full Scale Output: Minimum 170mV and Typical 200mV

Could you please suggest an appropriate instrumentation amplifier along with current source that meets these specifications? if available, please provide a reference circuit to facilitate the integration of the amplifier with the sensor.

Thank you for your time and support

regards,

Chandra

  • Hi Chandra,

    Can you provide some additional information about your application?

    • What is the desired signal gain / output voltage?
    • What supply voltage is available?
    • What is the operating temperature range?

    This will help me recommend the proper instrumentation amp and current source for your application.

    Thanks,

    Zach

  • Hi Zach,

    Thank you for your prompt response.

    Here are the details you requested:

    • Desired Signal Gain / Output Voltage: We plan to interface the instrumentation amplifier output to a single ended ADC with a signal level of 3.3V.
    • Available Supply Voltage: We have 5V and 3.3V supplies available on the proposed board.
    • Operating Temperature Range: The operating temperature range is from -20°C to +65°C.

    I appreciate your assistance in recommending the proper instrumentation amplifier and current source for our application.

    Regards,

    Chandra

  • Hi Chandra,

    The INA333 is a great option for your application.

    ti.com/product/INA333 

    This is a micropower instrumentation amp with a rail-to-rail output stage and zero-drift architecture that maintains a low offset voltage over temperature.

    See below a simulation using a gain of ~7.6 V/V based on an expected input differential of +/- 200mV. Of course, you may tweak the gain setting by changing the RG resistor to better accommodate your desired input and output signals. Simulation file is attached.

    INA333_LM234_Bridge_Sensor.TSC

    If you are interfacing a SAR ADC with a high sample rate, you may require an additional gain stage using a faster op-amp to drive the ADC. It is more common for a pressure sensor application to have a relatively low sample rate, in which case the additional gain stage is not necessary.

    For your 1mA excitation current, I can recommend the LM234 which has a temperature range of -25°C to 100°C.

    https://www.ti.com/product/LM234 

    The LM234 datasheet (https://www.ti.com/lit/ds/symlink/lm234.pdf) shows an application circuit designed to cancel the temperature coefficient which will provide a more accurate current over temperature. See figure 15 from LM234 datasheet.

    Regards,

    Zach

  • Hi Zach,

    Thanks for suggesting the INA333 and LM234 along with the supporting simulation result. The solution you provided looks great and fits well with our application.

    We are using a SAR ADC on the STM32H753 microcontroller, with a sampling rate less than 1 MHz. Given this setup, I agree that the INA333 should suffice for our needs, but I am considering whether an additional gain stage might still be beneficial to ensure optimal signal conditioning for the ADC.

    Could you please provide further guidance on whether an additional gain stage is necessary for our sampling rate, and if so, could you recommend a suitable faster op-amp to drive the ADC?

    Thank you again for your assistance.

    Regards,

    Chandra

  • Hi Chandra,

    Thanks for the additional information. I do recommend an additional ADC driver stage for your circuit. For a 16-bits @1MSPS I recommend OPA388 for its wide (10MHz) bandwidth. OPA388 is a zero-drift, zero-crossover, rail-to-rail input and output amplifier which will maintain the high precision across your temperature range. 

    https://www.ti.com/product/OPA388 

    If you are using fewer bits or lower sampling rates you could also consider OPA387 which is similar to OPA388 but slightly slower at 5.7MHz.

    https://www.ti.com/product/OPA387 

    Looking at the schematic again, it is highly recommended to drive the INA333 reference pin with a low-impedance source. This will prevent voltage offsets due to the voltage divider effect with the INA333 internal resistors. If you do not have already have a reference driver on-board, consider using a dual package OPA2388 or OPA2387 and using the extra channel as your reference driver as shown below.

    https://www.ti.com/product/OPA2388 

    https://www.ti.com/product/OPA2387 

    INA333_Bridge_Sensor_ADC_Drive.TSC

    Best regards and good luck with your design,

    Zach

  • Hi Zach,

    Thanks for your response and the recommendations on the gain amplifier.

    We plan to use the dual package to provide a low-impedance source for the INA333 reference pin. The simulation results look good. Thanks for the schematic.

    We will proceed with this design.

    Regards,

    Chandra