AN-6755 Datasheet, PDF (1/9 Pages) Fairchild Semiconductor – Design Guideline to Replace FAN6753 with FAN6755

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AN-6755
Design Guideline to Replace FAN6753 with FAN6755
Introduction
FAN6755 is a highly integrated PWM controller featuring
green-mode, frequency hopping, constant power limit, and a
number of protection functions. Green mode and burst
mode function with a low operating current to maximize the
light-load efficiency so the power supply can meet stringent
standby power regulations. Frequency hopping reduces the
Electro-Magnetic Emission (EMI) by spreading the
frequency spectrum. The constant power limit function
minimizes the component stress in abnormal conditions and
helps optimize the power stage. Protection functions such as
brownout, overload/open-loop (OLP), over-voltage (OVP),
and over-temperature (OTP) are fully integrated, which
improves the reliability of switched-mode power supplies
(SMPS) without increasing system cost. This application
note explains how to replace PWM controller FAN6753
with FAN6755. Only VIN and Latch pins are different;
however, some functional improvements have been made to
FAN6755 for higher efficiency, lower power consumption,
and better performance. Therefore, several external
components should be changed accordingly. Table 1
summarizes the differences between these two devices. The
operating current is reduced to achieve lower standby power
consumption, which allows less than 100mW standby
power consumption for most of LCD monitor power supply
designs. The typical application circuit and internal block
diagram are shown in Figure 1 and Figure 2, respectively.
Table 1. Comparison of FAN6753 and FAN6755
HV Pin Input Voltage
Brownout Protection
Line Voltage Compensation for Pulse-by-Pulse
Current Limit (V / V )
limit-L limit-H
Sense Pin Short-Circuit Protection (SCP)
Gate Source Current
FB Impedance (Z )
FB
Operating Current (I )
DD-OP
Leading-Edge Blanking Time (t )
LEB
Minimum Operating Voltage (UVLO)
Maximum Duty Cycle
Soft-Start (t )
SS
Package
FAN6753
500V
No
Saw-Limit (0.9V/0.56V)
V_SENSE<0.15V Longer than 150µs
250mA
5KΩ
2.7mA
150ns
9.5V
65%
5.0ms
8-Pin SOP Package
FAN6755
700V
Line Sensing Using VIN Pin
Adjusted by VIN Pin (0.83V/0.7V)
No
700mA
15KΩ
2mA
290ns
7.8V
75%
5.5ms
7-Pin SOP Package
© 2009 Fairchild Semiconductor Corporation
Rev. 1.0.2 • 1/14/11
www.fairchildsemi.com