SBOSA61B April   2021  – December 2021 OPA3S2859-EP

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revison History
  5. 5 Pin Configuration and Functions
  6. 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 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Programmable Gain
      2. 8.3.2 Slew Rate
      3. 8.3.3 Input and ESD Protection
    4. 8.4 Device Functional Modes
      1. 8.4.1 Split-Supply and Single-Supply Operation
      2. 8.4.2 Power-Down Mode
      3. 8.4.3 Gain Select Mode (SEL)
      4. 8.4.4 Latch Mode
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Examples
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Support Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

9.2.2 Detailed Design Procedure

The OPA3S2859-EP meets the growing demand for wideband, low-noise photodiode amplifiers. The closed-loop bandwidth of a transimpedance amplifier is a function of the following:

  1. The total input capacitance (CIN). This total includes the photodiode capacitance, the input capacitance of the amplifier (common-mode and differential capacitance) and any stray capacitance from the PCB.
  2. The op amp gain bandwidth product (GBWP).
  3. The transimpedance gain (RF).

Figure 9-1 shows the OPA3S2859-EP configured as programmable gain TIA using different feedback paths through the switch network. The feedback resistance (RF) and the input capacitance (CIN) form a zero in the noise gain that results in instability if left unchecked. To counteract the effect of the zero, a pole is inserted into the noise gain transfer function by adding the feedback capacitor (CF). The Transimpedance Considerations for High-Speed Amplifiers Application Report discusses theories and equations that show how to compensate a transimpedance amplifier for a particular transimpedance gain and input capacitance. The bandwidth and compensation equations from the application report are available in an Excel® calculator. What You Need To Know About Transimpedance Amplifiers – Part 1 provides a link to the calculator.

The equations and calculators in the referenced application report and blog posts are used to model the bandwidth (f–3dB) and noise performance of the OPA3S2859-EP configured as a TIA. For this setup, to emulate an ideal current source, choose RIN value to be 1 to 10x greater than RF such that the low frequency noise gain closer to 1 V/V to 2 V/V (RF = 1 kΩ, 10 kΩ, 100 kΩ, RIN = 10 kΩ, 100 kΩ, 100 kΩ; respectively). The resultant performance is shown in Figure 9-2. To maximize bandwidth, make sure to reduce any stray parasitic capacitance from the PCB. Increasing RF results in lower bandwidth. To maximize the signal-to-noise ratio (SNR) in an optical front-end system, maximize the gain in the TIA stage.