ML4818 Datasheet, PDF (1/12 Pages) Fairchild Semiconductor – Phase Modulation/Soft Switching Controller

May 1997
ML4818*
Phase Modulation/Soft Switching Controller
GENERAL DESCRIPTION
The ML4818 is a complete phase modulation control IC
suitable for full bridge soft switching converters. Unlike
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.
FEATURES
s Full bridge phase modulation zero voltage switching
circuit with programmable ZV transition times
s Constant frequency operation to 500kHz
s Current mode operation
s Cycle-by-cycle current limiting with integrating fault
detection and restart delay
s Precision buffered 5V reference (+1%)
s Four 1.5A peak current totem-pole output drivers
s Under-voltage lockout circuit with 6V hysteresis
s Power DIP package allows higher dissipation
* Some Packages Are Obsolete)
BLOCK DIAGRAM
SHUTDOWN
10
CLOCK
13
11 ^RT
2 ^CT
OSC
RAMP
3
E/A OUT
5
0.7V
+
+
ΦMOD
–
INV
8
+5V
–
ERROR
+^AMP
SOFT START
9
3V
–
+
V+
I₁
R
Q
S
12
RC_RESET
I_LIM
4
1V
I₂
+
–
R
Q
S
REFERENCE
AND
UNDER-VOLTAGE
LOCKOUT
INHIBIT
OUTPUTS
V_{REF 24}
V_{CC 20}
Q
T FLIP
FLOP
TQ
DELAY
DELAY
A2 OUT
16
V_CC
A1 OUT
17
R
SQ
DELAY
V_CC
B1 OUT
22
V_CC
DELAY
*PINS 1, 6, 7, 15, 18, 19 AND 23 ARE GND
B2 OUT
21
R_{DELAY 14}
GND
*
1