SBOS730A April 2015  – May 2015 LMH6401


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Options
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1Absolute Maximum Ratings
    2. 7.2ESD Ratings
    3. 7.3Recommended Operating Conditions
    4. 7.4Thermal Information
    5. 7.5Electrical Characteristics
    6. 7.6SPI Timing Requirements
    7. 7.7Typical Characteristics
  8. Parameter Measurement Information
    1. 8.1Setup Diagrams
    2. 8.2Output Measurement Reference Points
    3. 8.3ATE Testing and DC Measurements
    4. 8.4Frequency Response
    5. 8.5Distortion
    6. 8.6Noise Figure
    7. 8.7Pulse Response, Slew Rate, and Overdrive Recovery
    8. 8.8Power Down
    9. 8.9VOCM Frequency Response
  9. Detailed Description
    1. 9.1Overview
    2. 9.2Functional Block Diagram
    3. 9.3Feature Description
    4. 9.4Device Functional Modes
      1. 9.4.1Power-On Reset (POR)
      2. 9.4.2Power-Down (PD)
      3. 9.4.3Thermal Feedback Control
      4. 9.4.4Gain Control
    5. 9.5Programming
      1. 9.5.1Details of the Serial Interface
      2. 9.5.2Timing Diagrams
    6. 9.6Register Maps
      1. 9.6.1Revision ID (address = 0h, Read-Only) [default = 03h]
      2. 9.6.2Product ID (address = 1h, Read-Only) [default = 00h]
      3. 9.6.3Gain Control (address = 2h) [default = 20h]
      4. 9.6.4Reserved (address = 3h) [default = 8Ch]
      5. 9.6.5Thermal Feedback Gain Control (address = 4h) [default = 27h]
      6. 9.6.6Thermal Feedback Frequency Control (address = 5h) [default = 45h]
  10. 10Application and Implementation
    1. 10.1Application Information
      1. 10.1.1Analog Input Characteristics
      2. 10.1.2 Analog Output Characteristics
        1. Capacitive Loads
      3. 10.1.3Thermal Feedback Control
        1. Response Optimization using Thermal Feedback Control
      4. 10.1.4Thermal Considerations
    2. 10.2Typical Application
      1. 10.2.1Design Requirements
      2. 10.2.2Detailed Design Procedure
        1. ADCs
          1. Considerations
          2. Considerations
          3. Input Common-Mode Voltage Considerations—AC-Coupled Input
          4. Input Common-Mode Voltage Considerations—DC-Coupled Input
      3. 10.2.3Application Curves
    3. 10.3Do's and Don'ts
      1. 10.3.1Do:
      2. 10.3.2Don't:
  11. 11Power-Supply Recommendations
    1. 11.1Single-Supply Operation
    2. 11.2Split-Supply Operation
  12. 12Layout
    1. 12.1Layout Guidelines
    2. 12.2Layout Examples
  13. 13Device and Documentation Support
    1. 13.1Documentation Support
      1. 13.1.1Related Documentation
    2. 13.2Community Resources
    3. 13.3Trademarks
    4. 13.4Electrostatic Discharge Caution
    5. 13.5Glossary
  14. 14Mechanical, Packaging, and Orderable Information

12 Layout

12.1 Layout Guidelines

When dealing with a device with relatively high gain and bandwidth in excess of 1 GHz, certain board layout precautions must be taken to ensure stability and optimum performance. TI recommends that the LMH6401 board be multi-layered to improve thermal performance, grounding, and power-supply decoupling. The differential input and output traces must be symmetrical in order to achieve the best linearity performance.

By sandwiching the power-supply layer between ground layers on either side (with thin dielectric thicknesses), parasitic capacitance between power and ground functions as a distributed, high-resonance frequency capacitor to help with power-supply decoupling. The LMH6401 evaluation board includes a total of six layers and the positive (VS+) and negative (VS–) power planes are sandwiched in the middle with a board stack-up (dielectric thickness), as shown in Figure 71, to help with supply decoupling. Both VS+ and VS– must be connected to the internal power planes through multiple vias in the immediate vicinity of the supply pins. In addition, low ESL, ceramic, 0.01-μF decoupling capacitors to the supplies are placed on the same layer as the device to provide supply decoupling.

Routing high-frequency signal traces on a PCB requires careful attention to maintain signal integrity. A board layout software package can simplify the trace thickness design to maintain impedances for controlled impedance signals. In order to isolate the affect of board parasitic on frequency response, TI recommends placing the external output matching resistors close to the amplifier output pins. A 0.01-µF bypass capacitor is also recommended close to the VOCM pins to suppress high-frequency common-mode noise. Refer to the user guide LMH6401EVM Evaluation Module (SLOU406) for more details on board layout and design.

In order to improve board mechanical reliability, the LMH6401 has square anchor pins on four corners of the package that must be soldered to the board for mechanical strength.

LMH6401 LayerStackup_sbos730.gifFigure 71. Recommended PCB Layer Stack-Up for a Six-Layer Board

12.2 Layout Examples

LMH6401 LMH6401EVM_TopLayer.gifFigure 72. EVM Top Layer
LMH6401 LMH6401EVM_SecondLayer.gifFigure 73. EVM Second Layer Showing a Solid GND Plane