ML4823 Datasheet, PDF (1/9 Pages) Fairchild Semiconductor – High Frequency Power Supply Controller

May 1997
ML4823*
High Frequency Power Supply Controller
GENERAL DESCRIPTION
The ML4823 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 for single-ended applications
using voltage or current mode and provides for input
voltage feed forward.
A 1V threshold current limit comparator provides cycle-
by-cycle current limit and exceeding a 1.4V threshold
initiates a soft-start cycle. The soft start pin doubles as a
maximum duty cycle clamp. All logic is fully latched to
provide jitter-free operation and prevent multiple pulsing.
An under-voltage lockout circuit with 800mV of hysteresis
assures low startup current and drives the outputs low
during fault conditions.
This controller is an improved second source for the
UC3823 controller; however, the ML4823 includes
features not found on the 3823. These features are set in
italics.
FEATURES
s Practical operation at switching frequencies to 1.0MHz
s High current (2A peak) totem pole output
s Wide bandwidth error amplifier
s Fully latched logic with double pulse suppression
s Pulse-by-pulse current limiting
s Soft start and max. duty cycle control
s Under voltage lockout with hysteresis
s 5.1V trimmed bandgap reference
s Low start-up current (1.1mA)
s Pin compatible improved replacement for UC3823
s Fast shut down path from current limit to output
s Soft start latch ensures full soft start cycle
s Outputs pull low for undervoltage lockout
*Some Packages Are Obsolete
BLOCK DIAGRAM (Pin Configuration Shown for 16-Pin Version)
R_T
5
6 ^CT
OSC
CLOCK OUT
4
RAMP
7
1.25V
+
E/A OUT
3
NI
2
INV
1
+
ERROR
AMP
–
SOFT START
8
ILIM REF
11
9
ILIM/S.D.
–
+
+
1.4V ^–
+
COMP
–
V+
–
+ _1V
R
Q
S
R
Q
S
– _4V
+
5.1V
ENABLE
V_REF
VREF GEN
– ^9V
UNDER ⁺
VOLTAGE
LOCKOUT
INTERNAL
BIAS
POWER V_{C 13}
OUTPUT
14
POWER GND ₁₂
5.1V V_{REF 16}
V_{CC 15}
SIGNAL GND
10
1