May 1997
ML4828*
BiCMOS Phase Modulation/Soft Switching Controller
GENERAL DESCRIPTION
The ML4828 is a complete BiCMOS phase modulation
control IC suitable for full bridge soft switching converters.
Unlike conventional PWM circuits, the phase modulation
technique allows for zero voltage switching (ZVS)
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 ML4828 can be operated in either voltage or current
mode. Both cycle-by-cycle current limit, integrating fault
detection, and soft start reset are provided. The under-
voltage lockout circuit features a 1.5V hysteresis with a
low starting current to allow off-line start up with a bleed
resistor. A shutdown function powers down the IC, putting
it into a low quiescent state.
The circuit can be operated at frequencies up to 1MHz.
The ML4828 contains four high current CMOS outputs
which feature high slew rate with low cross conduction.
FEATURES
s
s
s
s
s
s
s
5V BiCMOS for low power and high frequency
(1MHz) operation
Full bridge phase modulation zero voltage switching
circuit with independent programmable delay times
Current or voltage mode operation capability
Cycle-by-cycle current limiting with integrating fault
detection and restart delay
Can be externally synchronized
Four 3Ω CMOS output drivers
Under-voltage lockout circuit with 1.5V hysteresis
*Some Packages Are End Of Life
BLOCK DIAGRAM
V
CC
14
V
REF
5
SYNC R
T
6
3
C
T
4
2.5V REF
SDN 19
UVLO
OSC
DRIVER
18 A1
EA+ 10
EA–
EAO
9
8
+
–
ERROR
AMP
ISS
Q
DELAY A
–
+
ΦMOD
T
Q
DRIVER
16 A2
RAMP 11
SS 7
2.5V
1.25V
Q
S
R
DRIVER
15 B1
+
Q
–
Q
R
RST 12
I
LIM
IRST
FAULT
LOGIC
S
DELAY B
Q
DRIVER
13 B2
I
LIM
20
1V
+
–
17
GND
1
R
A
2
R
B
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
