SNVSBZ3 June   2021 LM5168-Q1


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  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
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Control Architecture
      2. 8.3.2  Internal VCC Regulator and Bootstrap Capacitor
      3. 8.3.3  Internal Soft Start
      4. 8.3.4  On-Time Generator
      5. 8.3.5  Current Limit
      6. 8.3.6  N-Channel Buck Switch and Driver
      7. 8.3.7  Synchronous Rectifier
      8. 8.3.8  Enable/Undervoltage Lockout (EN/UVLO)
      9. 8.3.9  Power Good (PGOOD)
      10. 8.3.10 Thermal Protection
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Active Mode
      3. 8.4.3 Sleep Mode
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1.  Switching Frequency (RT)
        2.  Transformer Selection
        3.  Output Capacitor Selection
        4.  Secondary Output Diode
        5.  Regulation Comparator
        6.  Input Capacitor
        7.  Type-3 Ripple Network
        8.  Minimum Secondary Output Load
        9.  Example Design Summary
        10. Thermal Considerations
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Compact PCB Layout for EMI Reduction
      2. 11.1.2 Feedback Resistors
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Support Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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


The LM5169-Q1 and LM5168-Q1 are easy-to-use, ultra-low IQ constant on-time (COT) synchronous step-down buck regulators. With integrated high-side and low-side power MOSFETs, the LM516x-Q1 is a low-cost, highly efficient buck converter that operates from a wide input voltage of 6 V to 120 V, delivering up to 0.65-A or 0.3-A DC load current. The LM516x-Q1 is available in an 8-pin SO PowerPAD™ package with 1.27-mm pin pitch for adequate spacing in high-voltage applications. This constant on-time (COT) converter is ideal for low-noise, high-current, and fast load transient requirements, operating with a predictive on-time switching pulse. Over the input voltage range, input voltage feedforward is employed to achieve a quasi-fixed switching frequency. A controllable on time as low as 50 ns permits high step-down ratios and a minimum forced off time of 50 ns provides extremely high duty cycles, allowing VIN to drop close to VOUT before frequency foldback occurs. The LM516x-Q1 implements a smart peak and valley current limit detection circuit to ensure robust protection during output short circuit conditions. Control loop compensation is not required for this regulator, reducing design time and external component count.

The LM5169-Q1 and LM5168-Q1 are pre-programmed to operate in Auto mode or FPWM mode. When configured to operate in Auto mode, at light loads, the device transitions into an ultra-low IQ mode to maintain high efficiency and prevent draining battery cells connected to the input when the system is in standby. When configured in FPWM Mode, at light loads the device will maintain CCM operation enabling Fly-buck operation. The Fly-buck configuration can be used to generate both a non-isolated primary output and an isolated secondary output.

The LM5169-Q1 and LM5168-Q1 incorporates additional features for comprehensive system requirements, including an open-drain power-good circuit for the following:

  • Power-rail sequencing and fault reporting
  • Internally fixed soft start
  • Monotonic start-up into prebiased loads
  • Precision enable for programmable line undervoltage lockout (UVLO)
  • Smart cycle-by-cycle current limit for optimal inductor sizing
  • Thermal shutdown with automatic recovery

The LM5169-Q1 and LM5168-Q1 support a wide range of end equipment requiring a regulated output from a high input supply where the transient voltage deviates from its DC level. Examples of such end equipment systems are the following:

  • 48-V automotive systems
  • High cell-count battery-pack systems
  • 24-V industrial systems
  • 48-V telecom and PoE voltage ranges

The pin arrangement is designed for a simple layout that requires only a few external components.