ML4818 Datasheet, PDF (1/13 Pages) Fairchild Semiconductor – Phase Modulation/Soft Switching Controller

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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
General Description
The ML4818 is a complete phase modulation control IC suit-
able for full bridge soft switching converters. Unlike conven-
tional 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 cir-
cuit 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.
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
I₂
I_LIM
4
+
1V
–
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
*
REV. 1.0.3 6/21/01