Fairchild ML4826 service manual

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ML4826

PFC and Dual Output PWM Controller Combo

Features

• Internally synchronized PFC and PWM in one IC

• Low total harmonic distortion

• Low ripple current in the storage capacitor between the PFC and PWM sections

• Average current, continuous boost, leading edge PFC

• High efﬁciency trailing edge PWM with dual totem-pole outputs

• Average line voltage compensation with brown-out control

• PFC overvoltage comparator eliminates output “runaway” due to load removal

• Current-fed multiplier for improved noise immunity

• Overvoltage protection, UVLO, and soft start

Block Diagram

19

2

4

3

8

7

9

6

5

10

V

FB

2.5V

I

AC

V

RMS

I

SENSE

RAMP 1

RTC

T

RAMP 2

V

DC

V

CC

SS

DC I

LIMIT

VEA

-

+

8V

50µA

8V

20

VEAO

GAIN

MODULATOR

1.5V

11

AGND

3.5kΩ

IEA

-

+

3.5kΩ

-

+

IEAO

8V

OSCILLATOR

-

+

1

POWER FACTOR CORRECTOR

+

-

V

-

FB

2.5V

+

PULSE WIDTH MODULATOR

General Description

The ML4826 is a high power controller for power factor corrected, switched mode power supplies. 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 speciﬁcations. The ML4826 includes circuits for the implementation of a leading edge, average current “boost” type power factor correction and a trailing edge, pulse width modulator (PWM) with dual totem-pole outputs.

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 brown-out protection. The PWM section can be operated in current or voltage mode at up to 250kHz and includes a duty cycle limit to prevent transformer saturation.

17

V

7.5V

CC

PGND

V

CC2

PFC OUT

DUTY CYCLE

VIN OK

LIMIT

2.7V

-1V

1V

OVP

+

PFC I

-

+

-

LIMIT

DC I

LIMIT

V

CCZ

V

CCZ

13.5V

REFERENCE

SRQ

Q

SRQ

Q

STQ

Q

SRQ

Q

UVLO

V

REF

V

CC2

PWM 2

PWM 1

PGND

18

15

16

14

13

12

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ML4826 PRODUCT SPECIFICATION

Pin Conﬁguration

ML4826

20-Pin PDIP (P20)

IEAO

I

SENSE

V

RTC

RAMP 1

RAMP 2

DC I

I

AC

RMS

SS

V

DC

LIMIT

1

2

3

4

5

6

7

T

8

9

10

TOP VIEW

20

19

18

17

16

15

14

13

12

11

VEAO

V

FB

V

REF

V

CC2

V

CC1

PFC OUT

PWM 1

PWM 2

PGND

AGND

Pin Description

PIN NAME FUNCTION

1 IEAO PFC transconductance current error amplifier output

2I

3I

4V

AC

SENSE

RMS

5 SS Connection point for the PWM soft start capacitor

6V

7R

T

DC

C

8 RAMP 1 PFC ramp input

9 RAMP 2 When in current mode, this pin functions as the current sense input; when in voltage mode,

10 DC I

LIMIT

11 AGND Analog signal ground

12 PGND Return for the PWM totem-pole outputs

13 PWM 2 PWM driver 2 output

14 PWM 1 PWM drive 1 output

15 PFC OUT PFC driver output

16 V

17 V

18 V

19 V

CC2

CC1

REF

FB

20 VEAO PFC transconductance voltage error amplifier output

PFC gain control reference input

Current sense input to the PFC current limit comparator

Input for PFC RMS line voltage compensation

PWM voltage feedback input

Connection for oscillator frequency setting components

T

it is the PWM input from the PFC output (feedforward ramp)

PWM current limit comparator input

Positive supply for the PWM drive outputs

Positive supply (connected to an internal shunt regulator).

Buffered output for the internal 7.5V reference

PFC transconductance voltage error amplifier input

2

REV. 1.0.5 2/14/02

∆

Ω

PRODUCT SPECIFICATION ML4826

Absolute Maximum Ratings

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.

Parameter Min Max. Units

V

Shunt Regulator Current 55 mA

CC

I

Voltage on Any Other Pin GND – 0.3 V

I

Peak PFC OUT Current, Source or Sink 500 mA

Peak PWM OUT Current, Source or Sink 500 mA

PFC OUT, PWM 1, PWM 2 Energy Per Cycle 1.5 mJ

Junction Temperature 150 °C

Storage Temperature Range –65 150 °C

Lead Temperature (Soldering, 10 sec) 260 °C

Thermal Resistance ( θ Plastic DIP 67 °C/W

Voltage –3 5 V

SENSE

+ 0.3 V

CCZ

REF

Input Current 10 mA

AC

)

JA

20 mA

Operating Conditions

Parameter Min. Max. Units

Temperature Range ML4826CP2 0 70 °C

Electrical Characteristics

Unless otherwise speciﬁed, I T

= Operating Temperature Range (Note 1)

A

Symbol Parameter Conditions Min. Typ. Max. Units

Voltage Error Ampliﬁer

Input Voltage Range 0 7 V

Transconductance V

Feedback Reference Voltage 2.4 2.5 2.6 V

Input Bias Current Note 2 –0.3 –1.0 µA

Output High Voltage 6.0 6.7 V

Output Low Voltage 0.6 1.0 V

Source Current

Sink Current

Open Loop Gain 60 75 dB

Power Supply Rejection Ratio V

Current Error Ampliﬁer

Input Voltage Range -1.5 2 V

Transconductance V

Input Offset Voltage ±3 ±15 mV

Input Bias Current –0.5 –1.0 µA

= 25mA, R

CC

RAMP 1

= R

T

NON INV

V

= ±0.5V, V

IN

V

= ±0.5V, V

IN

– 3V < V

CCZ

NON INV

= 52.3k Ω , C

= V

, VEAO = 3.75V 50 85 120 µ Ω

INV

OUT

< V

CC

, VEAO = 3.75V 130 195 310 µ Ω

INV

= C

RAMP1

= 180 pF,

T

= 6V –40 –80 µA

= 1.5V 40 80 µA

– 0.5V 60 75 dB

CCZ

Ω

REV. 1.0.5 2/14/02

3

∆

∆(

ML4826 PRODUCT SPECIFICATION

Electrical Characteristics

Unless otherwise speciﬁed, I

= Operating Temperature Range (Note 1)

T

A

= 25mA, R

CC

(continued)

RAMP 1

= R

= 52.3k Ω , C

T

RAMP1

= C

= 180 pF,

T

Symbol Parameter Conditions Min. Typ. Max. Units

Output High Voltage 6.0 6.7 V

Output Low Voltage 0.6 1.0 V

Source Current

Sink Current

V

= ±0.5V, V

IN

V

= ±0.5V, V

IN

= 6V –40 –90 µA

OUT

= 1.5V 40 90 µA

OUT

Open Loop Gain 60 75 dB

Power Supply Rejection Ratio V

CCZ

– 3V < V

CC

< V

– 0.5V 60 75 dB

CCZ

OVP Comparator

Threshold Voltage 2.6 2.7 2.8 V

Hysteresis 80 115 150 mV

PFC I

Comparator

LIMIT

Threshold Voltage –0.8 –1.0 –1.15 V

PFC I

- Gain Modulator

LIMIT

100 190 mV

Output)

Delay to Output 150 300 ns

DC I

comparator

LIMIT

Threshold Voltage 0.9 1.0 1.1 V

Input Bias Current ±0.3 ±1 µA

Delay to Output 150 300 ns

V

OK Comparator

IN

Threshold Voltage 2.4 2.5 2.6 V

Hysteresis 0.8 1.0 1.2 V

Gain Modulator

Gain (Note 3) I

= 100µA, V

AC

I

= 50µA, V

AC

I

= 50µA, V

AC

I

= 100µA, V

AC

RMS

= V

= 0V 0.36 0.55 0.66

FB

= 1.2V, V

= 1.8V, V

= 3.3V, V

= 0V 1.20 1.80 2.24

FB

= 0V 0.55 0.80 1.01

FB

= 0V 0.14 0.20 0.26

FB

Bandwidth IAC = 100µA 10 MHz

Output Voltage I

= 250µA, V

AC

= 1.15V, V

RMS

= 0V 0.72 0.82 0.95 V

FB

Oscillator

Initial Accuracy T

Voltage Stability V

= 25°C 180 190 200 kHz

A

CCZ

– 3V < V

CC

< V

– 0.5V 1 %

CCZ

Temperature Stability 2 %

Total Variation Line, Temp 170 210 kHz

Ramp Valley to Peak Voltage 2.5 V

Dead Time PFC Only 250 500 ns

C

Discharge Current V

T

RAMP 1

= 0V, V(R

C

) = 2.5V 4.5 7.5 9.5 mA

T

RAMP 1 Discharge Current 5 mA

Reference

Output Voltage T

Line Regulation V

= 25°C, I(V

A

– 3V < V

CCZ

) = 1mA 7.4 7.5 7.6 V

REF

CC

< V

– 0.5V 2 10 mV

CCZ

4

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PRODUCT SPECIFICATION ML4826

Electrical Characteristics (continued)

Unless otherwise speciﬁed, I

= 25mA, R

CC

RAMP 1

TA = Operating Temperature Range (Note 1)

Symbol Parameter Conditions Min. Typ. Max. Units

Load Regulation 1mA < I(V

Total Variation Line, Load, Temp 7.25 7.65 V

Long Term Stability TJ = 125˚C, 1000 Hours 5 25 mV

PFC

Minimum Duty Cycle ML4826-2, V

Maximum Duty Cycle V

Output Low Voltage I

Output High Voltage I

Rise/Fall Time CL = 1000pF 50 ns

PWM

Duty Cycle Range 0-47 0-48 0-50 %

Output Low Voltage I

Output High Voltage I

Rise/Fall Time CL = 1000pF 50 ns

Supply

Shunt Regulator Voltage (V

)

CCZ

V

Load Regulation 25mA < ICC < 55mA ±150 ±300 mV

CCZ

V

Total Variation Load, temp 12.4 14.6 V

CCZ

Start-up Current VCC = 11.2V, CL = 0 0.7 1.1 mA

Operating Current VCC < V

Undervoltage Lockout Threshold

Undervoltage Lockout Hysteresis

Notes:

1. Limits are guaranteed by 100% testing, sampling, or correlation with worst-case test conditions.

2. Includes all bias currents to other circuits connected to the VFB pin.

3. Gain = K x 5.3V; K = (I

GAINMOD

- I

OFFSET

= RT = 52.3kΩ, C

) < 20mA 7 20 mV

REF

> 5.7V 0 %

IEAO

< 1.2V 90 95 %

IEAO

= –20mA 0.4 0.8 V

OUT

= –50mA 0.6 3.0 V

I

OUT

I

= 10mA, VCC = 8V 0.7 1.5 V

OUT

= 20mA 9.5 10.5 V

OUT

I

= 50mA 9.0 10 V

OUT

= –20mA 0.4 0.8 V

OUT

I

= –50mA 0.6 3.0 V

OUT

I

= 10mA, VCC = 8V 0.7 1.5 V

OUT

= 20mA 9.5 10.5 V

OUT

I

= 50mA 9.0 10 V

OUT

RAMP1

= CT = 180 pF,

12.8 13.5 14.2 V

– 0.5V, CL = 0 22 28 mA

CCZ

12 13 14 V

2.65 3.0 3.35 V

) x IAC x (VEAO - 1.5V)-1.

REV. 1.0.5 2/14/02 5

Fairchild ML4826 service manual

Specifications and Main Features

Frequently Asked Questions

User Manual