SNAS744A July 2017  – October 2017 LMS3655

PRODUCTION DATA. 

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  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. 7.5Thermal Information (for Device Mounted on PCB)
    6. 7.6Electrical Characteristics
    7. 7.7System Characteristics
    8. 7.8Timing Requirements
    9. 7.9Typical Characteristics
  8. Detailed Description
    1. 8.1Overview
    2. 8.2Functional Block Diagram
      1. 8.2.1Control Scheme
    3. 8.3Feature Description
      1. 8.3.1RESET Flag Output
      2. 8.3.2Enable and Start-Up
      3. 8.3.3Soft-Start Function
      4. 8.3.4Current Limit
      5. 8.3.5Hiccup Mode
      6. 8.3.6Synchronizing Input
      7. 8.3.7Undervoltage Lockout (UVLO) and Thermal Shutdown (TSD)
      8. 8.3.8Input Supply Current
    4. 8.4Device Functional Modes
      1. 8.4.1AUTO Mode
      2. 8.4.2FPWM Mode
      3. 8.4.3Dropout
      4. 8.4.4Spread-Spectrum Operation
  9. Application and Implementation
    1. 9.1Application Information
    2. 9.2Typical Applications
      1. 9.2.1General Application
        1. 9.2.1.1Design Requirements
        2. 9.2.1.2Detailed Design Procedure
          1. 9.2.1.2.1External Components Selection
            1. 9.2.1.2.1.1Input Capacitors
            2. 9.2.1.2.1.2Output Inductors and Capacitors
              1. 9.2.1.2.1.2.1Inductor Selection
              2. 9.2.1.2.1.2.2Output Capacitor Selection
          2. 9.2.1.2.2FB for Adjustable Output
          3. 9.2.1.2.3VCC
          4. 9.2.1.2.4BIAS
          5. 9.2.1.2.5CBOOT
          6. 9.2.1.2.6Maximum Ambient Temperature
        3. 9.2.1.3Application Curves
      2. 9.2.2Adjustable 5-V Output
        1. 9.2.2.1Design Requirements
        2. 9.2.2.2Detailed Design Procedure
        3. 9.2.2.3Application Curves
      3. 9.2.3Adjustable 3.3-V Output
        1. 9.2.3.1Design Requirements
        2. 9.2.3.2Detailed Design Procedure
        3. 9.2.3.3Application Curves
      4. 9.2.46-V Adjustable Output
        1. 9.2.4.1Design Requirements
        2. 9.2.4.2Detailed Design Procedure
        3. 9.2.4.3Application Curves
    3. 9.3Do's and Don't's
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1Layout Guidelines
    2. 11.2Layout Example
  12. 12Device and Documentation Support
    1. 12.1Device Support
      1. 12.1.1Third-Party Products Disclaimer
    2. 12.2Documentation Support
      1. 12.2.1Related Documentation
    3. 12.3Receiving Notification of Documentation Updates
    4. 12.4Community Resources
    5. 12.5Trademarks
    6. 12.6Electrostatic Discharge Caution
    7. 12.7Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Features

  • 96% Peak Efficiency While Converting 12 V to 5 V
  • Low EMI and Switch Noise
    • Minimized Switch Node Ringing
    • Pseudo-Random Spread Spectrum
  • 400-kHz (±10%) Fixed Switching Frequency
  • –40°C to +150°C Junction Temperature Range
  • External Frequency Synchronization
  • RESET Output With Internal Filter and 3-ms Release Timer
  • Automatic Light Load Mode for Improved Efficiency
  • Pin-Selectable Forced PWM Mode
  • Built-In Compensation, Soft Start, Current Limit, Thermal Shutdown, and UVLO
  • 0.35-V Dropout With 3.5-A Load at 25°C (Typical)
  • 32-µA IQ_VIN: Quiescent Current at 3.3 VOUT and No Load (Typical)
  • 5.5-A Continuous Load Current
  • Adjustable Output Voltage (1 V to 15 V)
  • ±1.5% Reference Voltage Tolerance
  • 4-mm × 5-mm, 0.5-mm Pitch SON Package

Applications

  • Noise-Sensitive Medical Applications
  • Telecom
  • High Performance Industrial

Description

The LMS3655 synchronous buck regulators are optimized for high performance applications, providing an adjustable output of 1 V to 15 V. Seamless transition between PWM and PFM modes, along with a low quiescent current, ensures high efficiency and superior transient responses at all loads.

Advanced high-speed circuitry allows the LMS3655 to regulate an input of 24 V to an output of 3.3 V at a fixed frequency of 400 kHz while also enabling a continuous load current of 5.5 A. An innovative frequency foldback architecture allows this device to regulate a 3.3-V output from an input voltage of only 3.5 V. The input voltage can range up to 36 V, with transient tolerance up to 42 V, easing input surge protection design.

An open-drain reset output, with built-in filtering and delay, provides a true indication of system status. This feature negates the requirement for an additional supervisory component, saving cost and board space.

Device Information(1)

DEVICE NAMEPACKAGEBODY SIZE
LMS3655VQFN-HR (22)4.00 mm × 5.00 mm
  1. For all available packages, see the orderable addendum at the end of the data sheet.

Typical Application Circuit

LMS3655 LMS3655-typical-application-SNAS744.gif

LMS3655 Efficiency: VOUT = 5 V

LMS3655 LMS3635-55-tc36-front-page-graph-efficiency-v-output-current-snas701.gif