March 2001

PRELIMINARY

ML4800

Power Factor Correction and PWM Controller Combo

GENERAL DESCRIPTION

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.

FEATURES

edge PWM in one IC

enhanced safety

for ultra-fast PFC response

µA startup current, 5.5mA operating

current

PFC and PWM sections

operation

start

BLOCK DIAGRAM

15

VEAO

IEAO

VFB

IAC

VRMS

ISENSE

RAMP 1

OSCILLATOR

OVP

PFC ILIMIT

UVLO

VREF

PULSE WIDTH MODULATOR

POWER FACTOR CORRECTOR

TRI-FAULT

2.5V

+

-

-

+

16

2

4

3

7.5V

REFERENCE

14

VCC

13

VCC

VEA

7

-

+

IEA

1

+

-

+

-

+

-

PFC OUT

12

S

R

Q

Q

S

R

Q

Q

2.75V

0.5V

-1V

RAMP 2

8

PWM OUT

11

S

R

Q

Q

VDC

6

SS

5

DC ILIMIT

9

VCC

DUTY CYCLE

LIMIT

-

+

1.0V

-

+

2.45V

VFB

-

+

VREF

VIN OK

GAIN

MODULATOR

VCC

1.6k

Ω

1.6k

Ω

1.25V

25µA

-

+

DC ILIMIT

17V

REV. 1.0.2 3/7/2001