AN4129 Datasheet, PDF (1/12 Pages) Fairchild Semiconductor – Green Current Mode PWM Controller FAN7601

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Application Note AN4129
Green Current Mode PWM Controller FAN7601
1. Introduction
This application note describes the operation and features of
the FAN7601. This device is a BCDMOS programmable
frequency current mode PWM controller which is designed
for off-line adapter applications and auxiliary power
supplies. To reduce power loss at light and no load, the
FAN7601 operates in burst mode and it includes a start-up
switch to reduce the losses in the start-up circuit.
Because of the internal start-up switch and burst mode oper-
ation, it is possible to supply an output power of 0.5W with
under 1W input power when the input line voltage is 265V.
On no load condition, input power is under 0.3W.
The FAN7601 offers a latch protection pin for the protection
of the system e.g. over voltage protection and/or thermal
shutdown.
The internal over voltage protection function shuts down the
IC operation when the supply voltage reaches 19V.
In addition, a soft start function is provided, and the soft start
time can be varied. Figure 1 shows a block diagram for the
FAN7601.
It contains the following blocks.
• Start-up circuit and reference
• Oscillator
• Soft start and latch
• Current sense and feed back
• Burst mode
• Output drive
Vref
8
Rt/Ct 4
OSC
Vref
12uA
Latch/SS 3
1.5V
OVP
+
−
2.5V
1V
GND 5
+
− _Start-up
Circuit
Vstr
1
Enable
5V Ref
Start-up
Circuit
OVP ₊
−
7 Vcc
19V
UVLO ₊
−
12V/8V
SQ
R
6 OUT
SQ
R
Reset
Circuit
Delay Circuit
+
−
0.97V/0.9V
2 CS/FB
+−−
Latch/SS
1V
©2003 Fairchild Semiconductor Corporation
Figure 1. Internal Block Diagram of the FAN7601
Rev. 1.0.1