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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
s
s
s
s
s
s
s
s
s
s
s
s
Practical operation at switching frequencies to 1.0MHz
High current (2A peak) totem pole output
Wide bandwidth error amplifier
Fully latched logic with double pulse suppression
Pulse-by-pulse current limiting
Soft start and max. duty cycle control
Under voltage lockout with hysteresis
5.1V trimmed bandgap reference
Low start-up current (1.1mA)
Pin compatible improved replacement for UC3823
Fast shut down path from current limit to output
Soft start latch ensures full soft start cycle
Outputs pull low for undervoltage lockout
BLOCK DIAGRAM
5
6
R
T
C
T
OSC
(Pin Configuration Shown for 16-Pin Version)
CLOCK OUT
4
7
3
RAMP
E/A OUT
1.25V
+
R
+
COMP
–
S
Q
2
1
NI
INV
+
ERROR
AMP
–
V+
POWER V
C
OUTPUT
POWER GND
–
+
–
+
ENABLE
V
REF
V
REF
GEN
–
+
9V
INTERNAL
BIAS
V
CC
SIGNAL GND
4V
13
14
12
8
SOFT START
I
LIM
REF
I
LIM
/S.D.
–
+
R
+
–
Q
S
UNDER
VOLTAGE
LOCKOUT
5.1V
11
9
1V
5.1V V
REF
16
1.4V
15
10
REV. 1.0 10/12/2000
ML4823
PIN CONFIGURATION
ML4823
16-PIN DIP (P16)
16-PIN SOIC (S16W)
INV
NI
E/A OUT
CLOCK
R
T
C
T
RAMP
SS
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
ML4823
20-PIN PLCC (Q20)
5.1V REF
20
5.1V REF
V
CC
OUTPUT
V
C
PWR GND
I
LIM
REF
GND
I
LIM
/S.D.
E/A OUT
CLOCK
NC
R
T
C
T
4
5
6
7
8
3
2
1
19
18
17
16
15
14
OUTPUT
V
C
NC
PWR GND
I
LIM
REF
TOP VIEW
9
10
11
12
13
I
LIM
/S.D.
RAMP
SS
TOP VIEW
PIN DESCRIPTION
PIN
NAME
(Pin Numbers in Parentheses are for PLCC Version)
PIN
NAME
FUNCTION
FUNCTION
1 (2)
2 (3)
3 (4)
4 (5)
5 (7)
INV
NI
Inverting input to error amp.
Non-inverting input to error amp.
9 (12) I
LIM
/S.D.
10 (13) GND
11 (14) I
LIM
REF
Current limit sense pin. Normally
connected to current sense resistor.
Analog signal ground.
Reference input for cycle-by-cycle
current limit comparator.
E/A OUT Output of error amplifier and input to
main comparator.
CLOCK
R
T
Oscillator output.
Timing resistor for oscillator — sets
charging current for oscillator timing
capacitor (pin 6).
Timing capacitor for oscillator.
Non-inverting input to main
comparator. Connected to C
T
for
Voltage mode operation or to current
sense resistor for current mode.
Normally connected to soft start
capacitor.
12 (15) PWR GND Return for the high current totem
pole output.
13 (17) V
C
14 (18) OUT B
15 (19) V
CC
16 (20) 5.1V REF
Positive supply for the high current
totem pole output.
High current totem pole output.
Positive supply for the IC.
Buffered output for the 5.1V voltage
reference.
6 (8)
7 (9)
C
T
RAMP
8 (10)
SS
2
GND
NC
V
CC
INV
NC
NI
REV. 1.0 10/12/2000
ML4823
ABSOLUTE MAXIMUM RATINGS
Absolute maximum ratings are those values beyond which
the device could be permanently damaged. Absolute
maximum ratings are stress ratings only and functional
device operation is not implied.
Supply Voltage (V
C
, V
CC
) ........................................... 30V
OUTPUT Current, Source or Sink
DC ....................................................................... 0.5A
Pulse (0.5µs) ......................................................... 2.0A
Analog Inputs
(INV, NI, RAMP, SS, I
LIM
) .................. GND –0.3V to 6V
CLOCK OUTPUT Current ...................................... –5mA
F/A OUT Current ...................................................... 5mA
SOFT START Sink Current ....................................... 20mA
R
T
Charging Current ............................................... –5mA
Junction Temperature ............................................ 125°C
Storage Temperature Range ..................... –65°C to 150°C
Lead Temperature (Soldering 10 sec.) .................... 260°C
Thermal Resistance (θ
JA
)
Plastic DIP ....................................................... 80°C/W
Plastic SOIC................................................... 105°C/W
Plastic Chip Carrier (PLCC) .............................. 78°C/W
OPERATING CONDITIONS
Temperature Range
ML4823C .................................................. 0°C to 70°C
ML4823I ................................................ –40°C to 85°C
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, R
T
= 3.65kΩ, C
T
= 1000pF, T
A
= Operating Temperature Range, V
CC
= 15V. (Note 1)
PARAMETER
OSCILLATOR
Initial Accuracy
Voltage Stability
Temperature Stability
Total Variation
Clock Out High
Clock Out Low
Ramp Peak
Ramp Valley
Ramp Valley to Peak
REFERENCE
Output Voltage
Line Regulation
Load Regulation
Temperature Stability
Total Variation
Output Noise Voltage
Long Term Stability
Short Circuit Current
ERROR AMPLIFIER
Input Offset Voltage
Input Bias Current
Input Offset Current
Open Loop Gain
1
≤
V
O
≤
4V
50
0.6
0.1
95
±30
3
1
mV
µA
µA
dB
T
J
= 25°C, I
O
= 1mA
10V
≤
V
CC
≤
30V
1mA
≤
I
O
≤
10mA
–40°C
≤
T
J
≤
150°C,
Line, load, temp.
10Hz to 10kHz
T
J
= 125°C, 1000 hrs,
V
REF
= 0V
–15
4.975
50
5
–50
25
–100
5.025
5.10
2
5
0.2
5.175
20
20
0.4
5.225
V
mV
mV
%
V
µV
mV
mA
2.6
0.7
1.6
Line, temp.
340
3.9
4.5
2.3
2.8
1.0
1.8
2.9
3.0
1.25
2.0
T
J
= 25°C,
10V
≤
V
CC
≤
30V,
360
400
0.2
5
460
440
2
kHz
%
%
kHz
V
V
V
V
V
CONDITIONS
MIN
TYP
MAX
UNITS
REV. 1.0 10/12/2000
3
ML4823
ELECTRICAL CHARACTERISTICS
PARAMETER
ERROR AMPLIFIER (Continued)
CMRR
PSRR
Output Sink Current
Output Source Current
Output High Voltage
Output Low Voltage
Unity Gain Bandwidth
Slew Rate
PWM COMPARATOR
RAMP Bias Current
Duty Cycle Range
E/A OUT Zero DC Threshold
Delay to Output
SOFT START
Charge Current
Discharge Current
CURRENT LIMIT/SHUTDOWN
I
LIM
Bias Current
Current Limit Offset
I
LIM
REF Common Mode Range
Shutdown Threshold
Delay to Output
OUTPUT
Output Low Level
I
OUT
= 20mA
I
OUT
= 200mA
Output High Level
I
OUT
= –20mA
I
OUT
= –200mA
Collector Leakage
Rise/Fall Time
UNDER VOLTAGE LOCKOUT
Start Threshold
UVLO Hysteresis
SUPPLY
Start Up Current
I
CC
Note 1:
(Continued)
CONDITIONS
MIN
TYP
MAX
UNITS
1.5
≤
V
CC
≤
5.5V
10
≤
V
CC
≤
30V
V
E/A OUT
= 1V
V
E/A OUT
= 4V
I
E/A OUT
= –0.5mA
I
E/A OUT
= 1mA
50
70
1
–0.5
4.0
0
3
6
80
100
2.5
–1.3
4.7
0.5
5.5
12
5.0
1.0
dB
dB
mA
mA
V
V
MHz
V/µs
V
RAMP
= 0V
0
V
RAMP
= 0V
1.1
–1
–5
80
µA
%
V
1.25
50
80
ns
V
SOFT START
= 0.5V
V
SOFT START
= 1V
0V
≤
I
LIM
≤
4V
I
LIM
REF = 1.1V
3
1
9
20
µA
mA
±10
0
1.0
1.25
1.40
50
15
1.25
1.55
80
µA
mV
V
V
ns
0.25
1.2
12.8
12.0
13.5
13.0
100
30
0.40
2.2
V
V
V
V
V
C
= 30V
C
L
= 1000pF
8.8
0.4
500
60
µA
ns
9.2
0.8
9.7
1.2
V
V
V
CC
= 8V
INV, RANP, I
LIM
= 0V
NI = 1V
1.1
22
2.5
33
mA
mA
Limits are guaranteed by 100% testing, sampling, or correlation with worst-case test conditions.
4
REV. 1.0 10/12/2000
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