ML4800 Datasheet, PDF (1/14 Pages) Fairchild Semiconductor – Power Factor Correction and PWM Controller Combo

March 2001
PRELIMINARY
ML4800
Power Factor Correction and PWM Controller Combo
GENERAL DESCRIPTION
FEATURES
The ML4800 is a controller for power factor corrected,
switched mode power supplies. Power Factor Correction
(PFC) allows the use of smaller, lower cost bulk capacitors,
reduces power line loading and stress on the switching
FETs, and results in a power supply that fully complies
with IEC1000-3-2 specification. Intended as a BiCMOS
version of the industry-standard ML4824, the ML4800
includes circuits for the implementation of leading edge,
average current, “boost” type power factor correction and
a trailing edge, pulse width modulator (PWM). It also
includes a TriFault Detect™ function to help ensure that no
unsafe conditions will result from single component failure
in the PFC. Gate-drivers with 1A capabilities minimize the
need for external driver circuits. Low power requirements
improve efficiency and reduce component costs.
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 input voltage
brownout protection. The PWM section can be operated in
current or voltage mode, at up to 250kHz, and includes an
accurate 50% duty cycle limit to prevent transformer
saturation.
I Internally synchronized leading-edge PFC and trailing-
edge PWM in one IC
I TriFault Detect™ for UL1950 compliance and
enhanced safety
I Slew rate enhanced transconductance error amplifier
for ultra-fast PFC response
I Low power: 200µA startup current, 5.5mA operating
current
I Low total harmonic distortion, high PF
I Reduced ripple current in storage capacitor between
PFC and PWM sections
I Average current, continuous boost leading edge PFC
I PWM configurable for current-mode or voltage mode
operation
I Current fed gain modulator for improved noise immunity
I Overvoltage and brown-out protection, UVLO, and soft
start
BLOCK DIAGRAM
16
VEAO
1
IEAO
VFB
15
2.5V
IAC
2
VRMS
4
ISENSE
3
VEA
-
+
1.6kΩ ^IEA
+
-
GAIN
MODULATOR
1.6kΩ
POWER FACTOR CORRECTOR
0.5V
+
TRI-FAULT
+
-
2.75V
OVP
+
-
-
-1V +
-
PFC ILIMIT
RAMP 1
7
OSCILLATOR
RAMP 2
8
DUTY CYCLE
LIMIT
VCC
17V
13
VCC
7.5V
REFERENCE
VREF
14
SQ
RQ
SQ
PFC OUT
12
RQ
VDC
6
VCC
SS
5
25µA
1.25V
DC ILIMIT _VREF
9
-
+
-
+
VFB
2.45V
VIN OK
-
+
1.0V
-
+
DC ILIMIT
PULSE WIDTH MODULATOR
VCC
SQ
RQ
PWM OUT
11
UVLO
REV. 1.0.2 3/7/2001