SNAS642A June   2014  – July 2014 LMK00804B

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Simplified Schematic
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1  Pin Characteristics
    2. 7.2  Absolute Maximum Ratings
    3. 7.3  Handling Ratings
    4. 7.4  Recommended Operating Conditions
    5. 7.5  Thermal Information
    6. 7.6  Power Supply Characteristics
    7. 7.7  LVCMOS / LVTTL DC Characteristics
    8. 7.8  Differential Input DC Characteristics
    9. 7.9  Electrical Characteristics (VDDO = 3.3 V ± 5%)
    10. 7.10 Electrical Characteristics (VDDO = 2.5 V ± 5%)
    11. 7.11 Electrical Characteristics (VDDO = 1.8 V ± 0.15 V)
    12. 7.12 Electrical Characteristics (VDDO = 1.5 V ± 5%)
    13. 7.13 Typical Characteristics
  8. 8 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
      1. 9.2.1 25
    3. 9.3 Feature Description
      1. 9.3.1 Clock Enable Timing
    4. 9.4 Device Functional Modes
      1. 9.4.1 Clock Input Function
  10. 10Applications and Implementation
    1. 10.1 Application Information
    2. 10.2 Output Clock Interface Circuit
    3. 10.3 Input Detail
    4. 10.4 Input Clock Interface Circuits
    5. 10.5 Typical Applications
      1. 10.5.1 Design Requirements
      2. 10.5.2 Detailed Design Procedure
      3. 10.5.3 Application Curves
        1. 10.5.3.1 System-Level Phase Noise and Additive Jitter Measurement
    6. 10.6 Do's and Don'ts
      1. 10.6.1 Power Considerations
      2. 10.6.2 Recommendations for Unused Input and Output Pins
      3. 10.6.3 Input Slew Rate Considerations
  11. 11Power Supply Recommendations
    1. 11.1 Power Supply Considerations
      1. 11.1.1 Power-Supply Filtering
      2. 11.1.2 Thermal Management
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Ground Planes
      2. 12.1.2 Power Supply Pins
      3. 12.1.3 Differential Input Termination
      4. 12.1.4 LVCMOS Input Termination
      5. 12.1.5 Output Termination
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
    2. 13.2 Trademarks
    3. 13.3 Electrostatic Discharge Caution
    4. 13.4 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

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発注情報

11 Power Supply Recommendations

11.1 Power Supply Considerations

While there is no strict power supply sequencing requirement, it is generally best practice to sequence the core supply voltage (VDD) before the output supply voltage (VDDO).

11.1.1 Power-Supply Filtering

High-performance clock buffers are sensitive to noise on the power supply, which can dramatically increase the additive jitter of the buffer. Thus, it is essential to reduce noise from the system power supply, especially when jitter or phase noise is critical to applications.

Use of filter capacitors eliminates the low-frequency noise from power supply, where the bypass capacitors provide the very low-impedance path for high-frequency noise and guard the power-supply system against induced fluctuations. The bypass capacitors also provide instantaneous current surges as required by the device, and should have low ESR. To use the bypass capacitors properly, place them very close to the power supply terminals and lay out traces with short loops to minimize inductance. TI recommends to adding as many high-frequency (for example, 0.1 µF) bypass capacitors as there are supply terminals in the package. It is recommended, but not required, to insert a ferrite bead between the board power supply and the chip power supply to isolate the high-frequency switching noises generated by the clock driver, preventing them from leaking into the board supply. Choosing an appropriate ferrite bead with very low DC resistance is important, because it is imperative to provide adequate isolation between the board supply and the chip supply. It is also imperative to maintain a voltage at the supply terminals that is greater than the minimum voltage required for proper operation.

0016.gifFigure 20. Power-Supply Decoupling

11.1.2 Thermal Management

For reliability and performance reasons, limit the die temperature to a maximum of 125°C. That is, as an estimate, TA (ambient temperature) plus device power consumption times θJA should not exceed 125°C.

Assuming the conditions in the Power Considerations section and operating at an ambient temperature of 70°C with all outputs loaded, here is an estimate of the LMK00804B junction temperature:

Equation 11. TJ= TA+ PTotal x θJA= 70 °C + (124 mW x 116 °C/W) = 70 °C + 14.4 °C = 84.4 °C

Here are some recommendations for improving heat flow away from the die:

  • Use multi-layer boards
  • Specify a higher copper thickness for the board
  • Increase the number of vias from the top level ground plane under and around the device to internal layers and to the bottom layer with as much copper area flow on each level as possible
  • Apply air flow
  • Leave unused outputs floating