SNVS738H October   2011  – June 2019 LMR24210

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Descriptions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Ratings
    4. 6.4 Electrical Characteristics
    5. 6.5 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  COT Control Circuit Overview
      2. 7.3.2  Start-up Regulator (VCC)
      3. 7.3.3  Regulation Comparator
      4. 7.3.4  Zero Coil Current Detect
      5. 7.3.5  Overvoltage Comparator
      6. 7.3.6  On-Time Timer, Shutdown
      7. 7.3.7  Current Limit
      8. 7.3.8  N-Channel Mosfet and Driver
      9. 7.3.9  Soft Start
      10. 7.3.10 Thermal Protection
      11. 7.3.11 Thermal Derating
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Detailed Design Procedure
        1. 8.2.1.1 Custom Design With WEBENCH® Tools
        2. 8.2.1.2 External Components
      2. 8.2.2 Application Curve
  9. 9 Layout
    1. 9.1 Layout Considerations
    2. 9.2 Layout Examples
    3. 9.3 Package Considerations
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
        1. 10.1.1.1 Custom Design With WEBENCH® Tools
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Community Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary

Package Options

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

7.3.6 On-Time Timer, Shutdown

The on-time of the LMR24210 main MOSFET is determined by the resistor RON and the input voltage VIN. It is calculated as follows:

Equation 4. LMR24210 30173823.gif

The inverse relationship of ton and VIN gives a nearly constant frequency as VIN is varied. RON should be selected such that the on-time at maximum VIN is greater than 150 ns. The on-timer has a limiter to ensure a minimum of 150 ns for ton. This limits the maximum operating frequency, which is governed by the following equation:

Equation 5. LMR24210 30173824.gif

The LMR24210 can be remotely shutdown by pulling the voltage of the EN pin below 1 V. In this shutdown mode, the SS pin is internally grounded, the on-timer is disabled, and bias currents are reduced. Releasing the EN pin allows normal operation to resume because the EN pin is internally pulled up.

LMR24210 30173825.pngFigure 17. Shutdown Implementation