SNAS660D June   2015  – May 2021 LM53600-Q1 , LM53601-Q1


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 System Characteristics
    7. 7.7 Timing Requirements
    8. 7.8 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Control Scheme
      2. 8.3.2 Soft-Start Function
      3. 8.3.3 Current Limit
      4. 8.3.4 Hiccup Mode
      5. 8.3.5 RESET Function
      6. 8.3.6 Forced PWM Operation
      7. 8.3.7 Auto Mode Operation and IQ_VIN
      8. 8.3.8 SYNC Operation
      9. 8.3.9 Spread Spectrum
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown
      2. 8.4.2 FPWM Operation
      3. 8.4.3 Auto Mode Operation
  9. Applications and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Off-Battery 5-V, 1-A Output Automotive Converter with Spread Spectrum
        1. Design Requirements
        2. Detailed Design Procedure
          1. Inductor Selection
          2. Output Capacitor Selection
          3. Input Capacitor Selection
          4. FB Voltage Divider for Adjustable Versions
          5. RPU - RESET Pull Up Resistor
        3. Application Curves
      2. 9.2.2 Off-Battery 3.3 V, 1 A Output Automotive Converter with Spread Spectrum
        1. Design Requirements
        2. Design Procedure
        3. Application Curves
    3. 9.3 Do's and Don't's
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Ground and Thermal Plane Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

Spread Spectrum

The spread spectrum is a factory option. In order to find which parts have spread spectrum enabled, see Section 5.

The purpose of the spread spectrum is to eliminate peak emissions at specific frequencies by spreading emissions across a wider range of frequencies than a part with fixed frequency operation. In most systems containing the LM53600-Q1 and LM53601-Q1 devices, low frequency conducted emissions from the first few harmonics of the switching frequency can be easily filtered. A more difficult design criterion is reduction of emissions at higher harmonics which fall in the FM band. These harmonics often couple to the environment through electric fields around the switch node. The LM53600-Q1 and LM53601-Q1 devices use a ±4% spread of frequencies which spread energy smoothly across the FM band but is small enough to limit sub-harmonic emissions below its switching frequency. Peak emissions at the part’s switching frequency are only reduced by slightly less than 1 dB, while peaks in the FM band are typically reduced by more than 6dB.

The LM53600-Q1 and LM53601-Q1 devices use a cycle to cycle frequency hopping method based on a linear feedback shift register (LFSR). Intelligent pseudo random generator limits cycle to cycle frequency changes to limit output ripple. Pseudo random pattern repeats by approximately 7 Hz which is below the audio band.

The spread spectrum is only available while the clock of the LM53600-Q1 and LM53601-Q1 devices is free running at its natural frequency. Any of the following conditions overrides spread spectrum, turning it off:

  1. An external clock is applied to the SYNC/MODE terminal.
  2. The clock is slowed due to operation low input voltage – this is operation in dropout.
  3. The clock is slowed due to high input voltage – input voltage above approximately 21 V disables spread spectrum.
  4. The clock is slowed under light load in Auto mode – this is normally not seen above 200 mA of load. In FPWM mode, spread spectrum is active even if there is no load.