ML4802 Datasheet, PDF (1/15 Pages) Fairchild Semiconductor – PFC/PWM Controller Combo with Green Mode

December 2000
PRELIMINARY
ML4802
PFC/PWM Controller Combo with Green Mode
GENERAL DESCRIPTION
The ML 4802 is a controller for power factor corrected,
switched mode power supplies that offers Green Mode
operation and reduced start-up and operating currents.
Green Mode is an efficiency improving circuit feature
which operates automatically in low power situations.
This feature helps meet the demands of Energy Star™
programs.
Power Factor Correction (PFC) offers the use of lower cost
bulk capacitors, reduces power line loading and stress on
the switching FETs. The ML4802 includes circuits for the
implementation of a leading edge, average current,
“boost” type power factor corrector and a trailing edge
Pulse Width Modulator (PWM).
The PFC frequency of the ML4802 is automatically
synchronized to be one half that of the PWM. This
technique allows the user to design with smaller PWM
components while maintaining the optimum operating
frequency for the PFC. An over-voltage comparator shuts
down the PFC section in the event of a sudden decrease
in load. The PFC section also includes peak current
limiting and brown-out protection.
FEATURES
s Internally synchronized PFC and PWM in one IC
s Green Mode maximizes efficiency during low power
standby operation
s Low supply current
(Start-up 200µA typ., operating 5.5mA typ.)
s Average current continuous boost leading edge PFC
s High efficiency trailing edge PWM can be configured
for current mode operation
s Reduced ripple current in the storage capacitor
between the PFC and PWM sections
s PFC overvoltage comparator eliminates output
“runaway” due to load removal
s Current fed gain modulator for improved noise
immunity
s Overvoltage protection, UVLO, and soft start
BLOCK DIAGRAM
VEAO
16
IEAO
1
VFB 15
2.5V
IAC 2
VRMS 4
ISENSE 3
VEA
-
+
1.8kΩ
IEA
+
–
GAIN
MODULATOR
8V
1.8kΩ
POWER FACTOR CORRECTOR
2.75V
+
- _OVP
PFC
CONTROLLER
-1V +
-
PFC ILIMIT
VCC
13
7.5V
REFERENCE
14 VREF
PFC
OUTPUT
DRIVER
12 PFC OUT
RAMP 1 8
RT/CT 7
RAMP 2 9
VDC 6
SS 5
8V
VLS
1.25V
-
+
VCC
25µA
8V
÷2
OSCILLATOR
DC LIMIT
VFB
VDC
GREEN
MODE
CONTROLLER
GREEN
MODE
VIN OK
DC ILIMIT
VFB -
+
-
2.43V +
+
1.5V -
PULSE WIDTH MODULATOR
PWM
OUTPUT
DRIVER
11 ^{PWM OUT}
REV. 1.0.1 12/12/2000