AN-6073 Datasheet, PDF (1/13 Pages) Fairchild Semiconductor – Highly Integrated Green-Mode PWM Controller

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AN-6073
FAN6751 — Highly Integrated Green-Mode PWM Controller
Introduction
This application note describes a detailed design strategy for
a high-efficiency, compact flyback converter. Design
considerations and mathematical equations are presented as
well as guidelines for a printed circuit board layout. The
highly integrated FAN6751 series of PWM controllers
provides several features to enhance the performance for
LCDM/TV, NB, and adapters.
The green-mode function includes off-time modulation and
burst mode to reduce the PWM frequency at light-load and
in no-load conditions. To avoid acoustic noise problems, the
minimum PWM frequency is set above 18KHz. 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. Built-in synchronized
slope compensation achieves stable peak-current-mode
control. The proprietary external line compensation ensures
constant output power limit over a wide AC input voltage
range, from 90V_AC to 264V_AC.
FAN6751 provides many protection functions, as shown in
Table 1. 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.
Features
ƒ High-Voltage Startup
ƒ Low Operating Current: 4mA
ƒ Linearly Decreasing PWM Frequency to 18KHz
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 Internal Recovery Circuit (OVP, OLP)
ƒ Internal Sense Short-Circuit Protection
ƒ External Constant Power Limit (Full AC Input Range)
ƒ Internal OTP Sensor with Hysteresis
ƒ Built-in 5ms Soft-Start Function
ƒ Built-in VIN Pin Pull HIGH (> 4.7V) Recovery
Function for Second-Side Output OVP
ƒ Brownout Protection with Hysteresis
Applications
General-purpose, switch-mode power supplies and flyback
power converters, including:
ƒ Power Adapters
ƒ Open-frame SMPS
ƒ LCD Monitor/TV
SOP-8
GND 1
FB 2
NC 3
HV 4
8 GATE
7 VDD
6 SENSE
5 VIN
Figure 1. Pin Configuration (Top View)
Table 1. Protection Functions of FAN6751 Series
Part Number
FAN6751MRMY
FAN6751HLMY
OVP (V_DD)
Recovery
Latch
OLP (FB)
Recovery
Latch
Pull-High
Protection (V_IN)
Recovery
Latch
© 2008 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 9/26/08
OTP
(Internal)
Recovery
Recovery
SCP
(SENSE)
Recovery
Recovery
PWM
Frequency
65KHz
100KHz
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