AN-6753 Datasheet, PDF (1/11 Pages) Fairchild Semiconductor – Highly Integrated Green-Mode PWM Controller

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AN-6753
FAN6753 — Highly Integrated Green-Mode PWM Controller
Abstract
This application note describes a detailed design strategy for
a high-efficiency compact flyback converter. Design
considerations, mathematical equations, and guidelines for a
Printed-Circuit-Board (PCB) layout are presented.
Features
ƒ High-Voltage Startup
ƒ Low Operating Current: 2.7mA
ƒ Linearly Decreasing PWM Frequency to 22KHz
ƒ Frequency Hopping to Reduce EMI Emission
ƒ Fixed PWM Frequency: 65KHz
ƒ Peak-Current-Mode Control
ƒ Cycle-by-Cycle Current Limiting
ƒ Leading-Edge Blanking (LEB)
ƒ Synchronized Slope Compensation
ƒ Internal Open-Loop Protection
ƒ Gate Output Maximum Voltage Clamp: 18V
ƒ V_DD Under-Voltage Lockout (UVLO)
ƒ V_DD Over-Voltage Protection (OVP)
ƒ Programmable Over-Temperature Protection (OTP)
ƒ Internal Latch Circuit (OTP)
ƒ Built-In 5ms Soft-Start Function
ƒ Constant Power Limit (Full AC Input Range)
ƒ Internal OTP Sensor with Hysteresis
Introduction
The highly integrated FAN6753 series of PWM controllers
provides several features to enhance the performance of
flyback converters.
To minimize standby power consumption, a proprietary
green-mode function provides off-time modulation to
linearly decrease the switching frequency at light-load
conditions. To avoid acoustic-noise problems, the minimum
PWM frequency is set above 22KHz. This green-mode
function enables the power supply to meet international
power conservation requirements. With the internal high-
voltage startup circuitry, the power loss due to bleeding
resistors is also eliminated. To further reduce power
consumption, FAN6753 is manufactured using the BiCMOS
process, which allows an operating current of only 2.7mA.
Built-in synchronized slope compensation achieves stable
peak-current-mode control. The proprietary external line
compensation ensures a constant output-power limit over a
wide AC input voltage range, from 90V_AC to 264V_AC.
FAN6753 provides many protection functions. In addition to
cycle-by-cycle current limiting, the internal open-loop
protection circuit ensures safety should an open-loop or
output short-circuit failure occur.
OVP (VDD)
OLP (FB)
FAN6753 Auto Restart Auto Restart
External Latch
(LATCH)
Latch
Applications
General-purpose, switch-mode power supplies and flyback
power converters, including:
ƒ Power Adapters
ƒ Open-Frame Switch-Mode Power Supply (SMPS)
SOP-8
RT 1
FB 2
SENSE 3
GND 4
8 HV
7 NC
6 VDD
5 GATE
Figure 1. Pin Configuration (Top View)
© 2009 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 5/13/09
www.fairchildsemi.com