SNVS799H April   2012  – November 2017 LM34927

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching 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 Overview
      2. 7.3.2  VCC Regulator
      3. 7.3.3  Regulation Comparator
      4. 7.3.4  Overvoltage Comparator
      5. 7.3.5  On-Time Generator
      6. 7.3.6  Current Limit
      7. 7.3.7  N-Channel Buck Switch and Driver
      8. 7.3.8  Synchronous Rectifier
      9. 7.3.9  Undervoltage Detector
      10. 7.3.10 Thermal Protection
      11. 7.3.11 Ripple Configuration
      12. 7.3.12 Soft Start
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Application Circuit: 20-V to 95-V Input and 10-V, 300-mA Output Isolated Fly-Buck Converter
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Transformer Turns Ratio
          2. 8.2.1.2.2  Total IOUT
          3. 8.2.1.2.3  RFB1, RFB2
          4. 8.2.1.2.4  Frequency Selection
          5. 8.2.1.2.5  Transformer Selection
          6. 8.2.1.2.6  Primary Output Capacitor
          7. 8.2.1.2.7  Secondary Output Capacitor
          8. 8.2.1.2.8  Type III Feedback Ripple Circuit
          9. 8.2.1.2.9  Secondary Diode
          10. 8.2.1.2.10 VCC and Bootstrap Capacitor
          11. 8.2.1.2.11 Input Capacitor
          12. 8.2.1.2.12 UVLO Resistors
          13. 8.2.1.2.13 VCC Diode
        3. 8.2.1.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Curves
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

1 Features

  • Wide 7.5-V to 100-V Input Range
  • Integrated 600-mA High-Side
    and Low-Side Switches
  • No Schottky Required
  • Constant On-Time Control
  • No Loop Compensation Required
  • Ultra-Fast Transient Response
  • Nearly Constant Operating Frequency
  • Intelligent Peak Current Limit
  • Adjustable Output Voltage From 1.225 V
  • Precision 2% Feedback Reference
  • Frequency Adjustable to 1 MHz
  • Adjustable Undervoltage Lockout (UVLO)
  • Remote Shutdown
  • Thermal Shutdown
  • Packages:
    • 8-pin WSON
    • 8-pin SO PowerPAD™

2 Applications

  • Isolated Telecom Bias Supply
  • Isolated Automotive and Industrial Electronics

3 Description

The LM34927 regulator features all of the functions needed to implement a low-cost, efficient, isolated bias regulator. This high-voltage regulator contains two 100-V N-channel MOSFET switches — a high-side buck switch and a low-side synchronous switch. The Constant on-time (COT) control scheme employed in the LM34927 device requires no loop compensation and provides excellent transient response. The regulator operates with an on-time that is inversely proportional to the input voltage. This feature allows the operating frequency to remain relatively constant. An intelligent peak current limit is implemented with integrated sense circuit. Other features include a programmable input undervoltage comparator to inhibit operation during low-voltage conditions. Protection features include thermal shutdown and VCC undervoltage lockout (UVLO). The LM34927 device is offered in WSON-8 and SO PowerPAD-8 plastic packages.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)
LM34927 SO PowerPAD (8) 4.89 mm × 3.90 mm
WSON (8) 4.00 mm × 4.00 mm
  1. For all available packages, see the orderable addendum at the end of the data sheet.

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Typical Application

LM34927 Typ App Schem.gif