SNVSB35C May   2018  – November 2024 LM26420-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics Per Buck
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Soft Start
      2. 6.3.2 Power Good
      3. 6.3.3 Precision Enable
    4. 6.4 Device Functional Modes
      1. 6.4.1 Output Overvoltage Protection
      2. 6.4.2 Undervoltage Lockout
      3. 6.4.3 Current Limit
      4. 6.4.4 Thermal Shutdown
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Programming Output Voltage
      2. 7.1.2 VINC Filtering Components
      3. 7.1.3 Using Precision Enable and Power Good
      4. 7.1.4 Overcurrent Protection for HTSSOP-20 Package
      5. 7.1.5 Current Limit and Short-Circuit Protection for WQFN-16 Package
    2. 7.2 Typical Applications
      1. 7.2.1 2.2-MHz, 0.8-V Typical High-Efficiency Application Circuit
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
          1. 7.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 7.2.1.2.2 Inductor Selection
          3. 7.2.1.2.3 Input Capacitor Selection
          4. 7.2.1.2.4 Output Capacitor
          5. 7.2.1.2.5 Calculating Efficiency and Junction Temperature
        3. 7.2.1.3 Application Curves
      2. 7.2.2 2.2-MHz, 1.8-V Typical High-Efficiency Application Circuit
        1. 7.2.2.1 Design Requirements
        2. 7.2.2.2 Detailed Design Procedure
        3. 7.2.2.3 Application Curves
      3. 7.2.3 LM26420-Q12.2-MHz, 2.5-V Typical High-Efficiency Application Circuit
        1. 7.2.3.1 Design Requirements
        2. 7.2.3.2 Detailed Design Procedure
        3. 7.2.3.3 Application Curves
    3. 7.3 Power Supply Recommendations
      1. 7.3.1 Power Supply Recommendations - HTSSOP-20 Package
      2. 7.3.2 Power Supply Recommendations - WQFN-16 Package
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
      3. 7.4.3 Thermal Considerations
        1. 7.4.3.1 Method 1: Silicon Junction Temperature Determination
        2. 7.4.3.2 Thermal Shutdown Temperature Determination
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
      2. 8.1.2 Custom Design With WEBENCH® Tools
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

6.1 Overview

The LM26420-Q1 is a constant frequency dual PWM buck synchronous regulator device that can supply two loads at up to 2 A each. The regulator has a preset switching frequency of 2.2 MHz . This high frequency allows the LM26420-Q1 to operate with small surface mount capacitors and inductors, resulting in a DC/DC converter that requires a minimum amount of board space. The LM26420-Q1 is internally compensated, so LM26420-Q1 is simple to use and requires few external components. The LM26420-Q1 uses current-mode control to regulate the output voltage. The following operating description of the LM26420-Q1 refers to the Section 6.2, which depicts the functional blocks for one of the two channels, and to the waveforms in Figure 6-1. The LM26420-Q1 supplies a regulated output voltage by switching the internal TOP and BOTTOM MOS switches at constant frequency and variable duty cycle. A switching cycle begins at the falling edge of the reset pulse generated by the internal clock. When this pulse goes low, the output control logic turns on the internal TOP switch. During this on-time, the SW pin voltage (VSW) swings up to approximately VIN, and the inductor current (IL) increases with a linear slope. IL is measured by the current sense amplifier, which generates an output proportional to the switch current. The sense signal is summed with the corrective ramp of the regulator and compared to the output of the error amplifier, which is proportional to the difference between the feedback voltage and VREF. When the PWM comparator output goes high, the TOP Switch turns off and the BOTTOM switch turns on after a short delay, which is controlled by the Dead-Time-Control Logic, until the next switching cycle begins. During the TOP switch off-time, inductor current discharges through the BOTTOM switch, which forces the SW pin to swing to ground. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage.

LM26420-Q1 LM26420-Q1 Basic Operation of the PWM ComparatorFigure 6-1 LM26420-Q1 Basic Operation of the PWM Comparator