May 1997
ML4825*
High Frequency Power Supply Controller
GENERAL DESCRIPTION
The ML4825 High Frequency PWM Controller is an IC
controller optimized for use in Switch Mode Power
Supply designs running at frequencies to 1MHz.
Propagation delays are minimal through the comparators
and logic for reliable high frequency operation while slew
rate and bandwidth are maximized on the error amplifier.
This controller is designed to work in either voltage or
current mode and provides for input voltage feed forward.
A 1V threshold current limit comparator provides cycle-
by-cycle current limit while exceeding a 1.4V threshold
initiates a soft-start cycle. The soft start pin doubles as a
maximum duty cycle clamp. An under-voltage lockout
circuit with 800mV of hysteresis assures low startup
current and drives the outputs low.
This controller is similar in architecture and performance
to the UC1825 controller, however the ML4825 includes
many features not found on the 1825. These features are
set in
Italics.
FEATURES
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Practical operation at switching frequencies to 1.0MHz
High current (2A peak) dual totem pole outputs
Wide bandwidth error amplifier
Fully latched logic with double pulse suppression
Pulse-by-pulse current limiting
Soft start and maximum duty cycle control
Under voltage lockout with hysteresis
Precision trimmed 5.1V bandgap reference
Pin compatible improved replacement for UC1825
Fast shut down path from current limit to outputs
Outputs preset to known condition after under voltage
lockout
Soft start latch ensures full soft start cycle
Outputs pull low for undervotage lockout
BLOCK DIAGRAM
(Pin configuration shown for 16-pin version)
5
6
*Some Packages Are Obsolete or End Of Life
CLOCK OUT
R
T
C
T
OSC
4
7
3
RAMP
E/A OUT
1.25V
+
R
+
–
COMP
S
Q
PWR V
C
OUT A
V+
C
TF.F.
P
Q
Q
POWER GND
POWER V
C
OUT B
PWR GND
–
+
+
2
1
NI
INV
+
–
ERROR
AMP
13
11
9µA
8
14
12
SS
4V
1V
ENABLE
V
REF
–
9
1V
I
LIM
/SD
–
+
1.5V V
REF
16
V
REF
GEN
R
Q
–
9V
INTERNAL
BIAS
V
CC
SIGNAL GND
15
10
+
1.4V
–
S
UNDER
VOLTAGE
LOCKOUT
+
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
