SNVS411D January   2006  – December 2025 LM25005

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 Resistance Characteristics
    5. 5.5 Electrical Characteristics
    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 High Voltage Start-Up Regulator
      2. 6.3.2 Oscillator and Sync Capability
      3. 6.3.3 Error Amplifier and PWM Comparator
      4. 6.3.4 RAMP Generator
      5. 6.3.5 Soft-Start
      6. 6.3.6 Current Limit
    4. 6.4 Device Functional Modes
      1. 6.4.1 Shutdown / Standby
      2. 6.4.2 Boost Pin
      3. 6.4.3 Thermal Protection
  8. 7 Application and Implementation
    1. 7.1 Application Information Disclaimer
    2. 7.2 Application Information
      1. 7.2.1 Bias Power Dissipation Reduction
    3. 7.3 Typical Application
      1. 7.3.1 Design Requirements
      2. 7.3.2 Detailed Design Procedure
        1. 7.3.2.1 Custom Design With WEBENCH® Tools
        2. 7.3.2.2 External Components
          1. 7.3.2.2.1  R3 (RT)
          2. 7.3.2.2.2  L1
          3. 7.3.2.2.3  C3 (CRAMP)
          4. 7.3.2.2.4  C9, C10
          5. 7.3.2.2.5  D1
          6. 7.3.2.2.6  C1, C2
          7. 7.3.2.2.7  C8
          8. 7.3.2.2.8  C7
          9. 7.3.2.2.9  C4
          10. 7.3.2.2.10 R5, R6
          11. 7.3.2.2.11 R1, R2, C12
          12. 7.3.2.2.12 R7, C11
          13. 7.3.2.2.13 R4, C5, C6
      3. 7.3.3 Application Curves
    4. 7.4 Power Supply Recommendations
    5. 7.5 Layout
      1. 7.5.1 Layout Guidelines
      2. 7.5.2 Layout Example
      3. 7.5.3 Power Dissipation
      4. 7.5.4 Thermal Design
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
      2. 8.1.2 Development Support
        1. 8.1.2.1 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 Export Control Notice
    8. 8.8 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

6.3.1 High Voltage Start-Up Regulator

The LM25005 contains a dual-mode internal high voltage startup regulator that provides the Vcc bias supply for the PWM controller and boot-strap MOSFET gate driver. The input pin (Vin) can be connected directly to the input voltage, as high as 42 Volts. For input voltages below 9V, a low dropout switch connects Vcc directly to Vin. In this supply range, Vcc is approximately equal to Vin. For Vin voltage greater than 9V, the low dropout switch is disabled and the Vcc regulator is enabled to maintain Vcc at approximately 7V. The wide operating range of 7V to 42V is achieved through the use of this dual mode regulator.

The output of the Vcc regulator is current limited to 20mA. Upon power up, the regulator sources current into the capacitor connected to the Vcc pin. When the voltage at the Vcc pin exceeds the Vcc UVLO threshold of 6.3V and the SD pin is greater than 1.225V, the output switch is enabled and a soft-start sequence begins. The output switch remains enabled until Vcc falls below 5.3V or the SD pin falls below 1.125V.

Apply an auxiliary supply voltage to the Vcc pin to reduce the IC power dissipation. If the auxiliary voltage is greater than 7.3V, the internal regulator essentially shuts off, reducing the IC power dissipation. The Vcc regulator series pass transistor includes a diode between Vcc and Vin. Do not forward bias the diode in normal operation. Therefore the auxiliary Vcc voltage never exceeds the Vin voltage.

In high voltage applications, take extra care to ensure that the Vin pin does not exceed the absolute maximum voltage rating of 45V. During line or load transients, voltage ringing on the Vin line that exceeds the Absolute Maximum Ratings can damage the IC. Both careful PC board layout and the use of quality bypass capacitors located close to the Vin and GND pins are essential.

LM25005 Vin and Vcc SequencingFigure 6-2 Vin and Vcc Sequencing