April 1997
ML4813
*
Flyback Power Factor Controller
1
GENERAL DESCRIPTION
The ML4813 is a PWM controller designed for use in a
discontinuous "flyback" or "buck-boost" type power factor
correction (PFC) system for low power, low cost
applications.
The circuit includes a precision reference, oscillator, error
amplifier, over-voltage comparator, over-current
comparator, and an extra op-amp as well as a high
current output. In addition, start-up is simplified by an
under-voltage lockout circuit.
In a typical application, the ML4813 functions as a
voltage mode regulator. By maintaining a constant duty
cycle, the current follows the input voltage, making the
impedance of the entire circuit appear purely resistive.
With the flyback circuit, power factors of 0.99 are easily
achievable with a small output inductor and a minimum
of external components.
FEATURES
s
Precision buffered 5V reference
s
Extra op-amp for output voltage instrumentation
amplifier
s
Overcurrent comparator for switch protection
s
Soft start and under-voltage lockout for easy low surge
off-line starting
s
1A peak current Totem-pole output drive
s
Overvoltage comparator eliminates output "runaway"
due to load removal
s
Large oscillator amplitude for better noise immunity
* This Part Is End Of Life As Of August 1, 2000
BLOCK DIAGRAM
-
+
+
-
S
R
Q
Q
12
OUT
4
VFB
ERROR
AMPLIFIER
5V
2
SOFT START
+
-
1
ILIMIT
CURRENT LIMIT
COMPARATOR
1V
5
OVP
OVP
COMPARATOR
5.6V
-
+
3
COMP
PWM
COMPARATOR
16
CT
9
RT
10
SYNC
OSCILLATOR
15
GND
UNDERVOLTAGE
LOCKOUT
13
VCC
14
VREF
32V
+
-
11
PWR GND
6
OA OUT
7V
7
OA-
8
OA+
60A
ML4813
2
PIN CONFIGURATION
PIN
NAME
FUNCTION
1
I
LIMIT
Current limit sense pin which is
normally connected to the sense
resistor. When I
LIMIT
exceeds 1V,
the PWM cycle is terminated
2
SOFT START
Connection for the soft start
capacitor
3
COMP
Output of error amplifier and input
to the PWM comparator
4
V
FB
Control loop feedback voltage
5
OVP
Overvoltage comparator input
6
OA OUT
Output of the uncommitted op
amp
7
OA-
Inverting input of the uncommitted
op amp
8
OA+
Non-inverting input of the
uncommitted op amp
PIN
NAME
FUNCTION
9
R
T
Connection for the oscillator
timing resistor
10
SYNC
Input for synchronizing the
oscillator to an external source
11
PWR GND
Return for the high current output
transistors
12
OUT
High current driver output
13
V
CC
Power supply input
14
V
REF
Buffered reference output
15
GND
Analog signal ground
16
C
T
Connection for the oscillator
timing capacitor
PIN DESCRIPTION
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
ILIMIT
SOFT START
COMP
VFB
OVP
OA OUT
OA-
OA+
CT
GND
VREF
VCC
OUT
PWR GND
SYNC
RT
TOP VIEW
ML4813
16-Pin PDIP (P16)
16-Pin SOIC (S16W)
ML4813
3
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 Current ....................................................... 40mA
OUT Current ............................................................. 1A
OUT Energy (capacitive load, per cycle) .................... 5J
COMP Sink Current ............................................... 10mA
C
T
Charging Current ................................................. 5mA
Analog Input Voltage (pins 1, 3-8) .... GND - 0.3V to 5.5V
Junction Temperature .............................................. 150C
Storage Temperature Range ..................... 65C to 150C
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, R
T
= 14k
W, C
T
= 1nF, T
A
= Operating Temperature Range (Notes 1, 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
OSCILLATOR
Initial Accuracy
T
j
= 25C
90
97
104
kHz
Voltage Stability 12V < V
CC
< 18V
0.3
%
Temperature Stability
2
%
Total Variation
Line, temp
88
108
kHz
Ramp Valley
1.0
V
Ramp Peak
4.3
V
R
T
Voltage
4.8
5.0
5.2
V
Discharge Current
T
j
= 25C, V(C
T
) = 2V
7.5
8.4
9.3
mA
V(C
T
) = 2V
7.2
8.4
9.5
mA
SYNC Threshold
0.8
1.4
2.0
V
SYNC Bias Current
350
800
A
REFERENCE
Output Voltage (V
REF
)
T
j
= 25C, I
REF
= 1mA
4.95
5.00
5.05
V
Line Regulation
12V < V
CC
< 25V
6
20
mV
Load Regulation 1mA < I
REF
< 20mA
3
20
mV
Temperature Stability
0.4
%
Total Variation
Line, load, temp
4.9
5.1
V
Output Noise
10Hz to 10kHz
50
V
Long Term Stability
T
j
= 125C, 1000 hours
5
25
mV
Short Circuit Current
V
REF
= GND
-30
-85
-180
mA
Lead Temperature (Soldering, 10 sec) ..................... 260C
Thermal Resistance (
q
JA
)
PDIP ................................................................ 88C/W
SOIC .............................................................. 105C/W
OPERATING CONDITIONS
Temperature Range
ML4813CX ................................................ 0C to 70C
ML4813IX ............................................... -40C to 85C
ML4813
4
ELECTRICAL CHARACTERISTICS
(cont.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ERROR AMPLIFIER
Input Offset Voltage
-15
15
mV
Input Bias Current
-0.1
-1.0
A
Open Loop Gain 1V < COMP < 5V
60
75
dB
PSRR
12V < V
CC
< 25V
60
70
dB
Output Sink Current
COMP = 1.1V, V
FB
= 6.2V
2
12
mA
Output Source Current
COMP = 5V, V
FB
= 4.8V
-0.5
-1.0
mA
Output High Voltage
I
COMP
= -0.5mA, V
FB
= 4.8V
5.3
6.4
V
Output Low Voltage
I
COMP
= 2mA, V
FB
= 6.2V
0.5
1.0
V
Unity Gain Bandwidth
1.0
MHz
UNCOMMITTED OP AMP
Input Offset Voltage
-10
10
mV
Input Bias Current
-0.1
-2.0
A
Input Offset Current
-350
350
nA
Open Loop Gain
90
dB
PSRR
80
125
dB
Output High Voltage
I
COMP
= -10mA
6.5
8
V
Output Low Voltage
R
L
= 10k
W
200
500
mV
I
LIMIT
COMPARATOR
Input Trip Point
0.8
1.0
1.2
V
Input Bias Current
-2
-15
A
Propogation Delay Time
150
ns
OVP COMPARATOR
Input Trip Point
5.4
5.55
5.7
V
Hysteresis
100
mV
Input Bias Current
-0.3
3
181A
PWM COMPARATOR
Input Common Mode Range
-0.2
5.5
V
Input Bias Current
-2
-10
A
Propogation Delay Time
150
ns
SOFT START
Soft Start Current
V
SOFT START
= 1V
40
65
90
A
ML4813
5
ELECTRICAL CHARACTERISTICS
(cont.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
OUTPUT
Output Low Voltage
I
OUT
= 10mA
0.1
0.4
V
I
OUT
= 200mA
1.2
2.2
V
V
CC
= 8V, I
OUT
= 5mA
0.1
0.8
V
Output High Voltage
I
OUT
= -20mA
13
13.6
V
I
OUT
= -200mA
12
13.4
V
Rise/Fall Time
C
L
= 1000pF
50
ns
UNDERVOLTAGE LOCKOUT
Start-up Threshold
15
16.3
17.5
V
Shutdown Threshold
9
10.1
11.2
V
V
REF
Good Threshold
4.4
V
SUPPLY
Start-up Current V
CC
= 14V
0.9
1.5
mA
Operating Current
20
30
mA
Shunt Regulator Voltage
I
CC
= 30mA
25
30
34
V
Note 1: Limits are guaranteed by 100% testing, sampling, or correlation with worst-case test conditions.
Note 2: VCC is raised above the UVLO start-up threshold, then returned to 15V.
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