SNOS966Q May   2001  – September 2014 LMH6642 , LMH6643 , LMH6644

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 Handling Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 3V Electrical Characteristics
    6. 7.6 5V Electrical Characteristics
    7. 7.7 ±5V Electrical Characteristics
    8. 7.8 Typical Performance Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 9.2.1.1 Input and Output Topology
        2. 9.2.1.2 Single Supply, Low Power Photodiode Amplifier
      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 Example
  12. 12Device and Documentation Support
    1. 12.1 Related Links
    2. 12.2 Trademarks
    3. 12.3 Electrostatic Discharge Caution
    4. 12.4 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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11 Layout

11.1 Layout Guidelines

Generally, a good high frequency layout will keep power supply and ground traces away from the inverting input and output pins. Parasitic capacitances on these nodes to ground will cause frequency response peaking and possible circuit oscillations (see Application Note OA-15, "Frequent Faux Pas in Applying Wideband Current Feedback Amplifiers", SNOA367, for more information). Texas Instruments suggests the following evaluation boards as a guide for high frequency layout and as an aid in device testing and characterization:

Table 1. Printed Circuit Board Layout And Component Values

DEVICE PACKAGE EVALUATION BOARD PN
LMH6642MF 5-Pin SOT-23 LMH730216
LMH6642MA 8-Pin SOIC LMH730227
LMH6643MA 8-Pin SOIC LMH730036
LMH6643MM 8-Pin VSSOP LMH730123
LMH6644MA 14-Pin SOIC LMH730231
LMH6644MT 14-Pin TSSOP LMH730131

Another important parameter in working with high speed/high performance amplifiers, is the component values selection. Choosing external resistors that are large in value will effect the closed loop behavior of the stage because of the interaction of these resistors with parasitic capacitances. These capacitors could be inherent to the device or a by-product of the board layout and component placement. Either way, keeping the resistor values lower, will diminish this interaction to a large extent. On the other hand, choosing very low value resistors could load down nodes and will contribute to higher overall power dissipation.

11.2 Layout Example

SNOS966_layer1_nologo_revised.pngFigure 59. LMH6642/LMH6643/LMH6644 Layer 1
SNOS966_layer2_nologo.pngFigure 60. LMH6642/LMH6643/LMH6644 Layer 2