AN-6014 Datasheet, PDF (1/15 Pages) Fairchild Semiconductor – Green Current Mode PWM Controller

www.fairchildsemi.com
Application Note AN-6014
Green Current Mode PWM Controller FAN7602
1. Introduction
The FAN7602 is a BCDMOS fixed-frequency current-mode
PWM controller designed for off-line power supplies. To
reduce the power loss at a light load and no load, the
FAN7602 operates in the burst mode and it includes a start-
up switch to reduce the loss of the IC start-up circuit.
Because of the internal start-up switch and the burst mode
operation, it is possible to supply 0.5W output load with
under 1W input power when the input line voltage is 265V.
On no load condition, the input power is under 0.3W.
The FAN7602 offers a latch protection pin for the system
protection, like over-voltage protection or/and thermal shut-
down. The internal V_CC over-voltage protection function
shuts down the IC when the supply voltage reaches 19V. Fur-
thermore, the internal soft-start function is provided and the
soft-start time is 10ms. It provides LUVP (Line Under-Volt-
age Protection) function for AC brown-in and brown-out
protection. OLP (Over Load Protection) protects the power
supply system against excessive load if the OLP condition
continues over 22ms. The switching frequency is internally
fixed a 65kHz and ±2kHz frequency modulation (FM) is
implemented for lower EMI. The frequency of FM is 125Hz.
And the Latch/Plimit pin can be used to limit the output
power over the entire input voltage range constantly.
Figure 1 shows the block diagram of the FAN7602.
The FAN7602 contains the following blocks:
„ Start-up circuit and soft-start
„ Clock with frequency modulation
„ Current sense and feedback with power limit
„ Overload protection
„ Burst mode
„ Line under-voltage protection
„ Latch protection
„ Output drive
LUVP 1
Latch/
Plimit
2
2V/1.5V
LUVP
OLP
OVP
Latch
Auto
Restart
Protection
Latch
Protection
10ms
Soft Start
SS End
65kHz Clock
with
Frequency
Modulation
Vstr
8
Reset
Circuit
Vcc
PWM
Block
Latch
4V
Plimit
Offset
Generator
Plimit
Offset
Soft
Start
OLP
OLP
SS End
OVP
6 Vcc
19V
5V Ref
UVLO
12V/8V
Driver
Circuit
Plimit
Offset
Delay
Circuit
0.95V/0.88V
PWM+
Soft
Start
Power Limit
Plimit
Offset
5 OUT
3 CS/FB
4 GND
Figure 1. Internal Block Diagram of the FAN7602
© 2006 Fairchild Semiconductor Corporation
FAN7602 Rev. 1.0.1
www.fairchildsemi.com