SBOS925A December   2020  – January 2021 OPA391

PRODUCTION DATA  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Low Input Bias Current
      2. 7.3.2 Input Differential Voltage
      3. 7.3.3 Capacitive Load Drive
      4. 7.3.4 EMI Rejection
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Three-Terminal CO Gas Sensor
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curve
      2. 8.2.2 4-mA to 20-mA Loop Design
        1. 8.2.2.1 Application Curve
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 TINA-TI™ Simulation Software (Free Download)
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

EMI Rejection

The OPA391 uses integrated electromagnetic interference (EMI) filtering to reduce the effects of EMI interference from sources such as wireless communications and densely-populated boards with a mix of analog signal chain and digital components. EMI immunity can be improved with circuit design techniques; the OPA391 benefits from these design improvements. Texas Instruments has developed the ability to accurately measure and quantify the immunity of an operational amplifier over a broad frequency spectrum extending from 10 MHz to 6 GHz. Figure 7-2 shows the results of this testing on the OPA391. Table 7-1 lists the EMIRR +IN values for the OPA391 at particular frequencies commonly encountered in real-world applications. Applications listed in Table 7-1 may be centered on or operated near the particular frequency shown. Detailed information can also be found in the EMI Rejection Ratio of Operational Amplifiers application report, available for download from www.ti.com.

The electromagnetic interference (EMI) rejection ratio, or EMIRR, describes the EMI immunity of operational amplifiers. An adverse effect that is common to many op amps is a change in the offset voltage as a result of RF signal rectification. An op amp that is more efficient at rejecting this change in offset as a result of EMI has a higher EMIRR and is quantified by a decibel value. Measuring EMIRR can be performed in many ways, but this section provides the EMIRR +IN, which specifically describes the EMIRR performance when the RF signal is applied to the noninverting input pin of the op amp. In general, only the noninverting input is tested for EMIRR for the following three reasons:

  1. Op amp input pins are known to be the most sensitive to EMI, and typically rectify RF signals better than the supply or output pins.
  2. The noninverting and inverting op amp inputs have symmetrical physical layouts and exhibit nearly matching EMIRR performance.
  3. EMIRR is more simple to measure on noninverting pins than on other pins because the noninverting input terminal can be isolated on a PCB. This isolation allows the RF signal to be applied directly to the noninverting input terminal with no complex interactions from other components or connecting PCB traces.

High-frequency signals conducted or radiated to any pin of the operational amplifier may result in adverse effects because the amplifier does not have sufficient loop gain to correct for signals with spectral content outside the bandwidth. Conducted or radiated EMI on inputs, power supply, or output may result in unexpected dc offsets, transient voltages, or other unknown behavior. Make sure to properly shield and isolate sensitive analog nodes from noisy radio signals, digital clocks, and interfaces.

The EMIRR +IN of the OPA391 is plotted versus frequency as shown in Figure 7-2. The OPA391 unity-gain bandwidth is 1 MHz. EMIRR performance less than this frequency denotes interfering signals that fall within the op amp bandwidth.

GUID-20210115-CA0I-4XGV-FNM6-LTV545MNQR7V-low.gif Figure 7-2 EMIRR Testing
Table 7-1 OPA391 EMIRR IN+ for Frequencies of Interest
FREQUENCYAPPLICATION AND ALLOCATIONEMIRR IN+
400 MHzMobile radio, mobile satellite, space operation, weather, radar, ultra-high frequency (UHF) applications39.1 dB
900 MHzGlobal system for mobile communications (GSM) applications, radio communication, navigation, GPS (to 1.6 GHz), GSM, aeronautical mobile, UHF applications46.5 dB
1.8 GHzGSM applications, mobile personal communications, broadband, satellite, L-band (1 GHz to 2 GHz)61.3 dB
2.4 GHz802.11b, 802.11g, 802.11n, Bluetooth®, mobile personal communications, industrial, scientific and medical (ISM) radio band, amateur radio and satellite, S-band (2 GHz to 4 GHz)69.8 dB
3.6 GHzRadiolocation, aero communication and navigation, satellite, mobile, S-band82.5 dB
5 GHz802.11a, 802.11n, aero communication and navigation, mobile communication, space and satellite operation, C-band (4 GHz to 8 GHz)83.6 dB