SNVS617H April   2009  – November 2014 LM25011 , LM25011-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Typical Application
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Handling Ratings: LM25011
    3. 6.3 Handling Ratings: LM25011-Q1
    4. 6.4 Recommended Operating Conditions
    5. 6.5 Thermal Information
    6. 6.6 Electrical Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Control Circuit Overview
      2. 7.3.2 On-Time Timer
      3. 7.3.3 Current Limit
      4. 7.3.4 Ripple Requirements
      5. 7.3.5 N-Channel Buck Switch and Driver
      6. 7.3.6 Soft-Start
      7. 7.3.7 Power Good Output (PGD)
      8. 7.3.8 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Function
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 LM25011 Example Circuit
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Custom Design with WEBENCH Tools
          2. 8.2.1.2.2 External Components
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Output Ripple Control
        1. 8.2.2.1 Option A: Lowest Cost Configuration
        2. 8.2.2.2 Option B: Intermediate VOUT Ripple Configuration
        3. 8.2.2.3 Option C: Minimum VOUT Ripple Configuration
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Power Dissipation
  11. 11Device and Documentation Support
    1. 11.1 Custom Design with WEBENCH Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Related Links
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.5 N-Channel Buck Switch and Driver

The LM25011 integrates an N-Channel buck switch and associated floating high-voltage gate driver. The gate driver circuit works in conjunction with an external bootstrap capacitor (CBST) and an internal high-voltage diode. A 0.1-µF capacitor connected between BST and SW provides the supply voltage for the driver during the on-time. During each off-time, the SW pin is at approximately –1 V, and CBST is recharged from the internal 5-V regulator for the next on-time. The minimum off-time ensures a sufficient time each cycle to recharge the bootstrap capacitor.

In applications with relatively high output voltage and low minimum load current, the internal pre-charge device of the LM25011 may not pull the SW pin sufficiently low during the off-time to maintain the voltage on the bootstrap capacitor. If the bootstrap capacitor (CBST) discharges during the long off-times, and the regulator will cycle on and off at a low frequency. Decreasing the values of the feedback resistors RFB1 and RFB2 to provide a minimum load of typically 1mA at nominal VOUT will increase the minimum switching frequency and maintain sufficient bootstrap capacitor voltage.