Linear Technology LTC3805 Flyback DC/DC Controller Application Note

This document provides detailed information on the design decisions made for a converter and describes methods for modifying the design for various applications. The document describes the design of an isolated version of the converter and the VCC power start-up method. It also explains how to program the output voltage by adjusting resistor values and how to select the frequency.


Linear Technology LTC3805 Flyback DC/DC Controller Application Note - cover page
Brand
Linear Technology
Category
Power Management
Document type
Application Note
Language
English
Pages
3
File format
PDF
File size
959 KB
Published
05 June, 2012
Updated
28 September, 2023
Model
LTC3805
MD5 checksum
2D6E96DB0113F4FD93B1714B66C869D7

About this manual

This document details the design decisions made when creating a flyback DC/DC converter using the LTC3805 controller. It describes methods for altering the design for various applications, including isolated versions. The text covers power and start-up configurations, output voltage programming, and frequency selection.

What's inside

  • VCC Power and Start-Up
  • Programming VOUT
  • Selecting Frequency
  • Programming the VIN Thresholds
  • Setting the Soft-Start
  • Programming Slope Compensation and Overcurrent Operation
  • Isolated Converter Design
  • Modifications for Different Input or Output Voltages
  • Frequency Synchronization

Specifications

Shutdown Current40µA
VCC Falling Threshold4V
RUN Pin Rising Threshold1.2V
Synchronization Lock-on Timetwo cycles
Synchronization Recovery Timetwo cycles

Frequently asked questions

How is the soft-start rate programmed?

The rate of change of VOUT at start-up is programmed by the capacitor on the SSFLT pin.

How is overcurrent protection set?

The overcurrent protection level is set by a resistor in series with the OC pin using a constant 10µA current sourced by the OC pin.

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