Fairchild Semiconductor ML4818 Datasheet

www.fairchildsemi.com

ML4818

Phase Modulation/Soft Switching Controller

Features

• Full bridge phase modulation zero voltage switching
circuit with programmable ZV transition times

• Constant frequency operation to 500kHz

• Current mode operation

• Cycle-by-cycle current limiting with integrating fault
detection and restart delay

• Precision buffered 5V reference (+1%)

• Four 1.5A peak current totem-pole output drivers

• Under-voltage lockout circuit with 6V hysteresis

• Power DIP package

Block Diagram

SHUTDOWN

10

CLOCK

13

R

T

11

2

3
5

C

T

RAMP
E/A OUT

OSC

0.7V

R

Q

+

+

ΦMOD

–

S

General Description

The ML4818 is a complete phase modulation control IC suit­able for full bridge soft switching converters. Unlik e conven­tional PWM circuits, the phase modulation technique allows
for zero-voltage switching transitions and square wave drive
across the transformer. The IC modulates the phases of the
two sides of the bridge to control output power.

The ML4818 can be operated in current mode. The delay
times for the outputs are externally programmable to allow
the zero-voltage switching transitions to take place.

Pulse-by-pulse current limit, integrating fault detection, and
soft start reset are provided. The under-voltage lockout cir­cuit features a 6V hysteresis with a low starting current to
allow off-line start up with a low power bleed resistor. A
shutdown function powers down the IC, putting it into a low
quiescent state.

REFERENCE

AND

UNDER-VOLTAGE

LOCKOUT

INHIBIT

OUTPUTS

A2 OUT

CC

T FLIP

FLOP

DELAY

V

V

REF

24

V

CC

20

16

INV

8

SOFT START

9

12

I

LIM

4

+5V

RC

3V

RESET

1V

–

ERROR

AMP

+

–

+

+

–

V+

I

1

R

Q

I

2

S

TQQ

R

SQ

*PINS 1, 6, 7, 15, 18, 19 AND 23 ARE GND

DELAY

V

DELAY

V

DELAY

A1 OUT

17

CC

B1 OUT

22

CC

B2 OUT

21

R

DELAY

14

GND

*

REV. 1.0.3 6/21/01

ML4818 PRODUCT SPECIFICATION

Pin Configuration

24-Pin Power DIP (P24)

V

GND

C

RAMP

I

LIM

E/A OUT

GND
GND

INV

SOFT START

SHUTDOWN

R

RC

RESET

T

T

24

1

23

2

22

3

21

4

20

5

19

6

18

7

17

8

16

9

15

10

14

11

13

12

TOP VIEW

REF

GND
B1 OUT
B2 OUT
V

CC

GND
GND
A1 OUT
A2 OUT
GND
R

DELAY

CLOCK

Pin Description

Pin Name Function

1 GND Ground
2CTTiming capacitor for oscillator
3 RAMP Non-inverting input to main comparator. Connected to current sense resistor for

current mode

4I

LIM

Current limit sense pin. Normally connected to current sense resistor

5 E/A OUT Output of error amplifier and input to PWM comparator

6,7 GND Ground and substrate

8 INV Inverting input to error amp
9 SOFT START Normally connected to soft start capacitor

10 SHUTDOWN Pulling this pin low puts the IC into a power down mode and turns off all outputs.

11 R
12 RC

T

RESET

This pin is internally pulled up to V
Resistor which sets discharge current for oscillator timing capacitor
Timing elements for Integrating fault detection and reset delay circuits

REF

.

13 CLOCK Oscillator output
14 R

DELAY

Resistor to ground on this pin programs the amount of delay from the time an

output turns off until its complementary output turns on
15 GND Ground
16 A2 OUT High current totem pole output A1
17 A1 OUT High current totem pole output A2

18,19 GND Ground and substrate

20 V

CC

Positive supply for the IC
21 B2 OUT High current totem pole output B1
22 B1 OUT High current totem pole output B2
23 GND Ground
24 V

REF

Buffered output for the 5V voltage reference

2 REV. 1.0.3 6/21/01

PRODUCT SPECIFICATION ML4818

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

CC

Output Driver Current, Source or Sink
DC
Pulse (0.5 µs)

Analog Inputs (CT, RAMP, I
RC

CLOCK Output Current (R
Error Amplifier Output Current (E/A OUT) 5 mA
SOFT START Sink Current 50 mA
Oscillator Charging Current (CT) –5mA
Junction Temperature 150 °C
Storage Temperature Range –65 150 °C
Lead Temperature (Soldering 10 Sec) 260 °C
Thermal Resistance (θJA)

Plastic Power DIP 40 °C/W

) –0.3 6 V

RESET

, E/A OUT, INV, SOFT START,

LIM

) –5mA

T

30 V

0.5

1.5

A
A

Operating Conditions

Parameter Min. Max. Units

Operating Temperature Range 0 70 °C

Electrical Characteristics

Unless otherwise specified, VCC = 15V, RT = 12.7kΩ, CT = 250pF, R
Temperature Range (Note 1).

Parameter Conditions Min. Typ. Max. Units

Oscillator

Initial Accuracy TA=25°C 410 450 525 kHz
Voltage Stability 12V<VCC<25V -0.3 %/V
Temperature Stability 0.2 %
Total Variation line, temp. 375 525 kHz
CT Discharge Current VCT=2V 4.7 5.5 6.3 mA
Clock Out High 2.4 3.1 6 V
Clock Out Low 0 0.4 V
Ramp Peak 0 4.1 V
Ramp Valley 1.5 5 V
Ramp Valley to Peak 0 2.6 5 V

Reference

Output Voltage TA=25°C, IO=1mA 4.95 5.0 5.05 V
Line Regulation 12V<VCC<25V -20 2 20 mV
Load Regulation 1mA<IO<10mA -20 3 20 mV

CLK

= 3kΩ, R

= 5kΩ, TA = Operating

DELAY

REV. 1.0.3 6/21/01 3

ML4818 PRODUCT SPECIFICATION

Electrical Characteristics (continued)

Unless otherwise specified, VCC = 15V, RT = 12.7kΩ, CT = 250pF, R
Temperature Range (Note 1).

Parameter Conditions Min. Typ. Max. Units

Temperature Stability 0.2 mV/°C
Total Variation 4.85 5.15 V
Output Noise Voltage 10Hz to 10kHz 50 mV
Long Term Stability T
Short Circuit Current V

=125°C, 1000 hrs 5 25 mV

j

=0V -20 -50 mA

REF

Error Amplifier

Input Offset Voltage -40 30 mV
Input Bias Current -3 0.6 3 µA
Input Offset Current 0.1 1 µA
Open Loop Gain 1 < V
PSRR 12 < V
Output Sink Current V
Output Source Current V
Output High Voltage I
Output Low Voltage I

< 4V 70 75 dB

O

< 25V 65 80 dB

CC
EA OUT
EA OUT

EA OUT
EA OUT

= 1V 1 3.2 mA

= 5.1V –0.5 –2.2 –20 mA
= –0.5mA 5.0 5.5 6.0 V
= 1mA 0.8 V

Unity Gain Bandwidth 2.0 2.8 MHz
Slew Rate 8.5 V/µs

Phase Modulator

RAMP Bias Current V
EA OUT Zero DC Threshold V

= 2.5V –1 –10 µA

RAMP

= 0V 0.4 0.6 0.9 V

RAMP

tPD, RAMP to Output 50 80 ns
t

DELAY

R

DELAY Voltage

CL = 1nF 99 200 250 ns

Soft Start

Charge Current V
Discharge Current V

SOFT START
SOFT START

= 4V –15 –25 –30 µA
= 1V 10 20 30 mA

Current Limit/Shutdown

I

Bias Current 0V < V

LIM

Current Limit Threshold V
tPD, I

LIM

RC
RC
RC

Shutdown Threshold 3.15 3.4 3.65 V

RESET

Restart Threshold 1.0 1.3 1.6 V

RESET

Charging Current V

RESET

SHUTDOWN

ILIM

< 4V –10 –110µA

ILIM

= 0V 0.92 1.02 1.12 V

=2V, V

RCRESET

SHUTDOWN Threshold 2.0 2.4 2.8 V
SHUTDOWN Input Bias Current V

SHUTDOWN

= 0 –100 –25 10 µA

CLK

= 3kΩ, R

= 5kΩ, TA = Operating

DELAY

4 4.3 5V V

50 ns

= 1.5V –400 –523 –1000 µA

4 REV. 1.0.3 6/21/01