ML4823IS 반도체 회로 부품 판매점
High Frequency Power Supply Controller
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 Micro Linear |
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)
5 RT
6 CT
OSC
CLOCK OUT
4
RAMP
7
1.25V
+
E/A OUT
3
NI
2
INV
1
+
ERROR
AMP
–
SOFT START
8
11 ILIM REF
9 ILIM/S.D.
–
+
+
1.4V –
+
COMP
–
V+
–
+ 1V
R
Q
S
R
Q
S
– 4V
+
5.1V
ENABLE
VREF
VREF GEN
– 9V
UNDER +
VOLTAGE
LOCKOUT
INTERNAL
BIAS
POWER VC 13
OUTPUT 14
POWER GND 12
5.1V VREF 16
VCC 15
SIGNAL GND 10
1
ML4823
PIN CONFIGURATION
ML4823
16-PIN DIP (P16)
16-PIN SOIC (S16W)
INV
NI
E/A OUT
CLOCK
RT
CT
RAMP
SS
1 16
2 15
3 14
4 13
5 12
6 11
7 10
89
TOP VIEW
5.1V REF
VCC
OUTPUT
VC
PWR GND
ILIM REF
GND
ILIM/S.D.
ML4823
20-PIN PLCC (Q20)
3 2 1 20 19
E/A OUT 4
18
CLOCK 5
17
NC 6
16
RT 7
15
CT 8
14
9 10 11 12 13
OUTPUT
VC
NC
PWR GND
ILIM REF
TOP VIEW
PIN DESCRIPTION (Pin Numbers in Parentheses are for PLCC Version)
PIN NAME FUNCTION
1 (2) INV
Inverting input to error amp.
2 (3) NI
Non-inverting input to error amp.
3 (4) E/A OUT Output of error amplifier and input to
main comparator.
4 (5) CLOCK Oscillator output.
5 (7) RT
Timing resistor for oscillator — sets
charging current for oscillator timing
capacitor (pin 6).
6 (8) CT
7 (9) RAMP
Timing capacitor for oscillator.
Non-inverting input to main
comparator. Connected to CT for
Voltage mode operation or to current
sense resistor for current mode.
8 (10) SS
Normally connected to soft start
capacitor.
PIN NAME FUNCTION
9 (12) ILIM/S.D. Current limit sense pin. Normally
connected to current sense resistor.
10 (13) GND
Analog signal ground.
11 (14) ILIM REF Reference input for cycle-by-cycle
current limit comparator.
12 (15) PWR GND Return for the high current totem
pole output.
13 (17) VC
Positive supply for the high current
totem pole output.
14 (18) OUT B High current totem pole output.
15 (19) VCC
16 (20) 5.1V REF
Positive supply for the IC.
Buffered output for the 5.1V voltage
reference.
2
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ML4823IS controller
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