SBOSAG2 june   2023 INA351A

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Device Comparison Table
  7. 6 Pin Configuration and Functions
  8. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Gain-Setting
        1. 8.3.1.1 Gain Error and Drift
      2. 8.3.2 Input Common-Mode Voltage Range
      3. 8.3.3 EMI Rejection
      4. 8.3.4 Typical Specifications and Distributions
      5. 8.3.5 Electrical Overstress
    4. 8.4 Device Functional Modes
  10. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Reference Amplifier
      2. 9.1.2 Input Bias Current Return Path
    2. 9.2 Typical Applications
      1. 9.2.1 Resistive-Bridge Pressure Sensor
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
        3. 9.2.1.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
        1. 10.1.1.1 PSpice® for TI
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Receiving Notification of Documentation Updates
    4. 10.4 Support Resources
    5. 10.5 Trademarks
    6. 10.6 Electrostatic Discharge Caution
    7. 10.7 Glossary
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DSG|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.1.2 Detailed Design Procedure

This section provides basic calculations to lay out the instrumentation amplifier with respect to the given design requirements.

One of the key considerations in resistive-bridge sensors is the common-mode voltage, VCM. If the bridge is balanced (no pressure, thus no voltage change), VCM(zero) is half of the bridge excitation (VEXT). In this example VCM (zero) is 2.5 V. For the maximum pressure of 12 psi, the bridge common-mode voltage, VCM(MAX), is calculated by:

Equation 1. VCM(MAX)= VDIFF2 + VCM(zero)

where

Equation 2. VDIFF=SMAX × VEXT × PMAX = 2.5 mVV× psi × 5 V × 12 psi = 150 mV

Thus, the maximum common-mode voltage applied results in:

Equation 3. VCM(MAX)=150 mV2+ 2.5 V=2.575 V

Similarly, the minimum common-mode voltage can be calculated as,

Equation 4. VCM(MIN)=-150 mV2+ 2.5 V=2.425 V

The next step is to calculate the gain required for the given maximum sensor output voltage span, VDIFF, in respect to the required VOUT swing of maximum 4.75V to avoid saturating the amplifier and the ADC running at 5V supply.

The following equation calculates the gain value using the maximum input voltage and the required output voltage:

Equation 5. G = V O U T V D I F F ( M A X ) = 2.25   V 150   m V = 15   V / V

Considering, INA351A is an INA in G = 10, an additional gain stage in G = 1.5 is added.

Next, let us make sure that the INA351A can operate within this range checking the Input Common-Mode Voltage vs Output Voltage curves in the Typical Characteristics section. The relevant figure is also in this section for convenience. Looking at Figure 9-5, we can confirm that a output signal swing of 3 V is supported for the input signal swing between 2.425 V and 2.575 V, thus making sure of the linear operation.

GUID-20221130-SS0I-7JPT-CRNW-S7SPW3N1B2NF-low.gif
VS = 5.5 V G = 10
Figure 9-5 Input Common-Mode Voltage vs Output Voltage (High CMRR Region)

An additional series resistor in the Wheatstone bridge string (R1) may or may not be required, and can be decided based on the intended output voltage swing for a particular combination of supply voltage, reference voltage and the selected gain for an input common mode voltage range. R1 helps adjust the input common-mode voltage range, and thus can help accommodate the intended output voltage swing. In this particular example, it is not required and can be shorted out.