Fairchild Semiconductor ML4805IS, ML4805CS, ML4805IP, ML4805CP Datasheet

November 1998

PRELIMINARY

ML4805

Variable Feedforward PFC/PWM Controller Combo

GENERAL DESCRIPTION

The ML4805 is a controller for power factor corrected,
switched mode power supplies. Similar to the ML4801,
the ML4805 may be used for voltage mode operation. Key
features of this combined PFC and PWM controller are
low start-up and operating currents. 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 IEC1000-2-3 specifications. The
ML4805 includes circuits for the implementation of a
leading edge, average current “boost” type power factor
correction and a trailing edge pulse width modulator.

The PFC frequency of the ML4805 is automatically set at
half that of the PWM frequency generated by the internal
oscillator. This technique allows the user to design with
smaller output components while maintaining the
optimum operating frequency for the PFC. An over­voltage 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.

BLOCK DIAGRAM

17

2

4

3

8

7

9

6

5

11

V

FB

2.5V

I

AC

V

RMS

I

SENSE

RAMP 1

RTC

T

RAMP 2

V

DC

V

SS

AGND

CC

VEAO

VEA

-

+

8V

25µA

8V

18

GAIN

MODULATOR

1.25V

1.6kΩ

IEA

+

–

1.6kΩ

-

+

IEAO

-

+

1

POWER FACTOR CORRECTOR

+

-

OSCILLATOR

V

-

FB

2.5V

+

PULSE WIDTH MODULATOR

FEATURES

■ Internally synchronized PFC and PWM in one IC

■ Low start-up current (200µA typ.)

■ Low operating current (5.5mA typ.)

■ Low total harmonic distortion

■ Reduces ripple current in the storage capacitor

between the PFC and PWM sections

■ Average current continuous boost leading edge PFC

■ High efficiency trailing edge PWM optimized for

voltage mode operation

■ Current fed gain modulator for improved noise

immunity

■ Brown-out control, overvoltage protection, UVLO, and

soft start

15

V

7.5V

REFERENCE

÷2

DUTY CYCLE

VIN OK

LIMIT

2.75V

-1V

1.5V

OVP

+

+

PFC I

+

-

-

-

LIMIT

DC I

LIMIT

V

CC

V

CC

SRQ

Q

SRQ

Q

SRQ

Q

UVLO

CC

V

REF

PFC OUT

PGND

PWM OUT

I

LIM

16

14

12

13

10

REV. 1.1 3/9/2001

ML4805

PIN CONFIGURATION

ML4805

18-Pin PDIP (P18)

18-Pin SOIC (S18)

IEAO

1

18

VEAO

I

SENSE

V

RMS

V

RTC

RAMP 1

RAMP 2

PIN DESCRIPTION

PIN NAME FUNCTION

1 IEAO PFC transconductance current error

amplifier output

2I

AC

3I

SENSE

PFC gain control reference input

Current sense input to the PFC current
limit comparator

I

AC

SS

DC

2

3

4

5

6

7

T

8

9

TOP VIEW

V

17

FB

V

16

REF

V

15

CC

PFC OUT

14

PWM OUT

13

PGND

12

AGND

11

I

10

LIM

PIN NAME FUNCTION

9 RAMP 2 PWM ramp sense input

10 ILIM PWM current limit sense input

11 AGND Analog ground

12 PGND Power ground

4V

RMS

Input for PFC RMS line voltage

13 PWM OUT PWM driver output

compensation

14 PFC OUT PFC driver output

5 SS Connection point for the PWM soft start

capacitor

15 V

CC

Positive supply (connected to an
internal shunt regulator).

6V

7R

DC

TCT

PWM voltage feedback input

Connection for oscillator frequency

16 V

REF

Buffered output for the internal 7.5V
reference

setting components

8 RAMP 1 PFC ramp input

17 V

FB

PFC transconductance voltage error
amplifier input

18 VEAO PFC transconductance voltage error

amplifier output

2 REV. 1.1 3/9/2001

ABSOLUTE MAXIMUM RATINGS

ML4805

Absolute maximum ratings are those values beyond which
the device could be permanently damaged. Absolute
maximum ratings are stress ratings only and functional
device operation is not implied.

Junction Temperature ............................................. 150°C

Storage Temperature Range ...................... –65°C to 150°C

Lead Temperature (Soldering, 10 sec) ..................... 260°C

Thermal Resistance (θ

)

JA

Plastic DIP ........................................................70°C/W

V

..............................................................................................

CC

Voltage .................................................. -3V to 5V

I

SENSE

Voltage on Any Other Pin ...... GND - 0.3V to V

I

...........................................................................................

REF

I

Input Current .....................................................10mA

AC

+ 0.3V

CC

18V

20mA

Peak PFC OUT Current, Source or Sink ................. 500mA

Peak PWM OUT Current, Source or Sink............... 500mA

PFC OUT, PWM OUT Energy Per Cycle ................... 1.5µJ

Plastic SOIC ...................................................100°C/W

OPERATING CONDITIONS

Temperature Range

ML4805CX ................................................. 0°C to 70°C

ML4805IX ............................................... -40°C to 85°C

ELECTRICAL CHARACTERISTICS

Unless otherwise specified, VCC = 15V, RT = 29.4kΩ, R
T

= Operating Temperature Range (Note 1)

A

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VOLTAGE ERROR AMPLIFIER

Input Voltage Range 0 5 V

Transconductance V

Feedback Reference Voltage 2.43 2.50 2.57 V

Input Bias Current Note 2 -0.5 -1.0 µA

Output High Voltage 6.0 6.7 V

Output Low Voltage 0.1 0.4 V

Source Current ∆VIN = ±0.5V, V

Sink Current ∆VIN = ±0.5V, V

Open Loop Gain 60 70 dB

PSRR 11V < VCC < 16.5V 60 70 dB

CURRENT ERROR AMPLIFIER

Input Voltage Range -1.5 2 V

Transconductance V

Input Offset Voltage 0 8 15 mV

Input Bias Current -0.5 -1.0 µA

Output High Voltage 6.0 6.7 V

Output Low Voltage 0.65 1.0 V

Source Current ∆VIN = ±0.5V, V

Sink Current ∆VIN = ±0.5V, V

Open Loop Gain 55 65 dB

PSRR 11V < VCC < 16.5V 60 75 dB

NON INV

NON INV

= 15.4kΩ, CT = 270pF, C

RAMP1

= V

, VEAO = 3.75V 40 65 80 µ

INV

= 6V -40 -70 -150 µA

OUT

= 1.5V 40 70 150 µA

OUT

= V

, VEAO = 3.75V 60 100 120 µ

INV

= 6V -40 -70 -150 µA

OUT

= 1.5V 40 70 150 µA

OUT

RAMP1

= 620pF,

Ω

Ω

REV. 1.1 3/9/2001 3

ML4805

ELECTRICAL CHARACTERISTICS (Continued)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

OVP COMPARATOR

Threshold Voltage 2.65 2.75 2.85 V

Hysteresis 175 250 325 mV

PFC I

DC I

VIN OK COMPARATOR

GAIN MODULATOR

OSCILLATOR

COMPARATOR

LIMIT

Threshold Voltage -0.9 -1.0 -1.1 V

∆PFC I

Threshold - Gain Modulator Output 120 220 mV

LIMIT

Delay to Output 150 300 ns

COMPARATOR

LIMIT

Threshold Voltage 1.4 1.5 1.6 V

Input Bias Current ±0.3 ±1 µA

Delay to Output 150 300 ns

Threshold Voltage 2.4 2.5 2.6 V

Hysteresis 0.8 1.0 1.2 V

Gain (Note 3) IAC = 100µA, V

IAC = 50µA, V

IAC = 50µA, V

IAC = 100µA, V

= VFB = 0V 0.65 0.85 1.05

RMS

= 1V, VFB = 0V 1.90 2.20 2.40

RMS

= 1.8V, VFB = 0V 0.90 1.05 1.25

RMS

= 3.3V, VFB = 0V 0.20 0.30 0.40

RMS

Bandwidth IAC = 100µA 10 MHz

Output Voltage I

= 350µA, V

AC

= 1V, 0.65 0.75 0.85 V

RMS

VFB = 0V

Initial Accuracy TA = 25ºC 188 200 212 kHz

Voltage Stability 11V < VCC < 16.5V 1 %

Temperature Stability 2%

Total Variation Line, Temp 182 218 kHz

Ramp Valley to Peak Voltage 2.5 V

PFC Dead Time 350 470 600 ns

CT Discharge Current V

RAMP 2

= 0V, V

= 2.5V 3.5 5.5 7.5 mA

RAMP 1

4 REV. 1.1 3/9/2001