SNCS103E November   2004  – August 2018 LMH6574

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Frequency Response vs VOUT
      2.      Frequency Response vs Gain
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
    2.     Truth Table
  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 ±5 V
    6. 6.6 Electrical Characteristics ±3.3 V
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Functional Block Diagram
    2. 7.2 Feature Description
      1. 7.2.1 Video Performance
      2. 7.2.2 Feedback Resistor Selection
      3. 7.2.3 Other Applications
      4. 7.2.4 Driving Capacitive Loads
      5. 7.2.5 ESD Protection
    3. 7.3 Device Functional Modes
      1. 7.3.1 SD vs EN
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Multiplexer Expansion
  9. 9 Power Supply Recommendations
    1. 9.1 Power Dissipation
  10. 10Layout
    1. 10.1 Layout Guidelines
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.2.2 Feedback Resistor Selection

LMH6574 20119732.gifFigure 27. Suggested RF vs Gain

The LMH6574 has a current feedback output buffer with gain determined by external feedback (RF) and gain set (RG) resistors. With current feedback amplifiers, the closed loop frequency response is a function of RF. For a gain of 2 V/V, the recommended value of RF is 575Ω. For other gains see Figure 27. Generally, lowering RF from the recommended value will peak the frequency response and extend the bandwidth while increasing the value of RF will cause the frequency response to roll off faster. Reducing the value of RF too far below the recommended value will cause overshoot, ringing and, eventually, oscillation.

Since all applications are slightly different it is worth some experimentation to find the optimal RF for a given circuit. For more information see Current Feedback Loop Gain Analysis and Performance Enhancement, Application Note OA-13 (SNOA366), which describes the relationship between RF and closed-loop frequency response for current feedback operational amplifiers. The impedance looking into pin 12 is approximately 20Ω. This allows for good bandwidth at gains up to 10 V/V. When used with gains over 10 V/V, the LMH6574 will exhibit a “gain bandwidth product” similar to a typical voltage feedback amplifier. For gains of over 10 V/V consider selecting a high performance video amplifier like the LMH6720 (SNOSA39) to provide additional gain.