www.docs.chipfind.ru
April 1998
ML4812
Power Factor Controller
GENERAL DESCRIPTION
The ML4812 is designed to optimally facilitate a peak
current control boost type power factor correction system.
Special care has been taken in the design of the ML4812
to increase system noise immunity. The circuit includes a
precision reference, gain modulator, error amplifier, over-
voltage protection, ramp compensation, as well as a high
current output. In addition, start-up is simplified by an
under-voltage lockout circuit with 6V hysteresis.
In a typical application, the ML4812 functions as a
current mode regulator. The current which is necessary to
terminate the cycle is a product of the sinusoidal line
voltage times the output of the error amplifier which is
regulating the output DC voltage. Ramp compensation is
programmable with an external resistor, to provide stable
operation when the duty cycle exceeds 50%.
BLOCK DIAGRAM
(Pin Configuration Shown is for DIP Version)
FEATURES
s
Precision buffered 5V reference (
0.5%)
s
Current-input gain modulator reduces external
components and improves noise immunity
s
Programmable ramp compensation circuit
s
1A peak current totem-pole output drive
s
Overvoltage comparator helps prevent output
voltage "runaway"
s
Wide common mode range in current sense
comparators for better noise immunity
s
Large oscillator amplitude for better noise immunity
5V
OVP
ISENSE
GM OUT
EA OUT
ISINE
RAMP COMP
CT
RT
ERROR
AMP
IEA
OSC
1k
UNDER
VOLTAGE
LOCKOUT
SHDN
OUT
PWR GND
VREF
VCC
GND
CLOCK
VCC
EA
32V
5
1
2
10
12
11
14
13
15
9
3
4
6
7
16
8
+
5V
+
5V
+
5V
S
R
Q
Q
GAIN MODULATOR
REV. 1.0 10/10/2000
ML4812
2
REV. 1.0 10/10/2000
PIN CONFIGURATION
PIN
NAME
FUNCTION
1
I
SENSE
Input from the current sense
transformer to the non-inverting input
of the PWM comparator.
2
GM OUT
Output of gain modulator.
A resistor to ground on this pin
converts the current to a voltage.
This pin is clamped to 5V and tied
to the inverting input of the PWM
comparator.
3
EA OUT
Output of error amplifier.
4
EA
Inverting input to error amplifier.
5
OVP
Input to over voltage comparator.
6
I
SINE
Current gain modulator input.
7
RAMP
COMP
Buffered output from the oscillator
ramp (C
T
). A resistor to ground sets the
current which is internally subtracted
from the product of I
SINE
and I
EA
in
the gain modulator.
PIN
NAME
FUNCTION
8
R
T
Oscillator timing resistor pin. A 5V
source sets a current in the external
resistor which is mirrored to charge
C
T
.
9
CLOCK
Digital clock output.
10
SHDN
A TTL compatible low level on this pin
turns off the output.
11
PWR GND Return for the high current totem pole
output.
12
OUT
High current totem pole output.
13
V
CC
Positive Supply for the IC.
14
V
REF
Buffered output for the 5V voltage
reference.
15
GND
Analog signal ground.
16
C
T
Timing capacitor for the oscillator.
PIN DESCRIPTION
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
ISENSE
GM OUT
EA OUT
EA
OVP
ISINE
RAMP COMP
RT
CT
GND
VREF
VCC
OUT
PWR GND
SHDN
CLOCK
TOP VIEW
ML4812
16-Pin PDIP (P16)
TOP VIEW
ML4812
20-Pin PLCC (Q20)
EA OUT
EA
NC
OVP
ISINE
VREF
VCC
NC
OUT
PWR GND
GM OUT
I SENSE
NC
C
T
GND
RAMP COMP
R
T
NC
CLOCK
SHDN
4
5
6
7
8
18
17
16
15
14
3
2
1 20 19
9 10 11 12 13
ML4812
REV. 1.0 10/10/2000
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 (I
CC
) ............................................... 30mA
Output Current Source or Sink (OUT) DC ................ 1.0A
Output Energy (capacitive load per cycle) .................. 5
J
Gain Modulator I
SINE
Input (I
SINE
) ......................... 1.2mA
Error Amp Sink Current (EA OUT) .......................... 10mA
Oscillator Charge Current ........................................ 2mA
Analog Inputs (I
SENSE
, EA, OVP) ............... 0.3V to 5.5V
Junction Temperature ............................................. 150
C
Storage Temperature Range ..................... 65
C to 150
C
Lead Temperature (soldering 10 sec.) ..................... 260
C
Thermal Resistance (
JA
)
20-Pin PLCC .................................................... 60
C/W
16-Pin PDIP .................................................... 65
C/W
OPERATING CONDITIONS
Temperature Range
ML4812CX ................................................ 0
C to 70
C
ML4812IX ............................................. 40
C to 85
C
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, V
CC
= 15V , R
T
= 14k
, C
T
= 1000pF, T
A
= Operating Temperature Range (Notes 1, 2).
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
OSCILLATOR
Initial Accuracy
T
J
= 25
C
91
98
105
kHz
Voltage Stability
12V < V
CC
< 18V
0.3
%
Temperature Stability
2
%
Total Variation
Line, temperature
90
108
kHz
Ramp Valley to Peak
3.3
V
R
T
Voltage
4.8
5.0
5.2
V
Discharge Current (R
T
open)
T
J
= 25
C, V
CT
= 2V
7.8
8.4
9.0
mA
V
CT
= 2V
7.3
8.4
9.3
mA
Clock Out Voltage Low
R
L
= 16k
0.2
0.5
V
Clock Out Voltage High
R
L
= 16k
3.0
3.5
V
REFERENCE
Output Voltage
T
J
= 25
C, I
O
= 1mA
4.95
5.00
5.05
V
Line Regulation
12V < V
CC
< 25V
2
20
mV
Load Regulation
1mA < I
O
< 20mA
2
20
mV
Temperature Stability
0.4
%
Total Variation
Line, load, temp.
4.9
5.1
V
Output Noise Voltage
10Hz to 10kHz
50
V
Long Term Stability
T
J
= 125
C, 1000 hours
5
25
mV
Short Circuit Current
V
REF
= 0V
30
85
180
mA
ERROR AMPLIFIER
Input Offset Voltage
15
mV
Input Bias Current
0.1
1.0
A
Open Loop Gain
1 < V
EA OUT
< 5V
60
75
dB
PSRR
12V < V
CC
< 25V
60
75
dB
Output Sink Current
V
EA OUT
= 1.1V, V
EA
= 6.2V
2
12
mA
Output Source Current
V
EA OUT
= 5.0V, V
EA
= 4.8V
0.5
1.0
mA
Output High Voltage
I
EA OUT
= 0.5mA, V
EA
= 4.8V
5.3
5.5
V
Output Low Voltage
I
EA OUT
= 1mA, V
EA
= 6.2V
0.5
1.0
V
Unity Gain Bandwidth
1.0
MHz
ML4812
4
REV. 1.0 10/10/2000
ELECTRICAL CHARACTERISTICS
(Continued)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
GAIN MODULATOR
I
SINE
Input Voltage
I
SINE
= 500
A
0.4
0.7
0.9
V
Output Current (GM OUT)
I
SINE
= 500
A, EA = V
REF
20mV
430
470
510
A
I
SINE
= 500
A, EA = V
REF
+ 20mV
3
10
A
I
SINE
= 1mA, EA = V
REF
20mV
860
940
1020
A
I
SINE
= 500
A, EA = V
REF
20mV,
455
A
I
RAMP COMP
= 50
A
Bandwidth
200
kHz
PSRR
12V < V
CC
< 25V
70
dB
OVP COMPARATOR
Input Offset Voltage
Output Off
25
+5
mV
Hysteresis
Output On
95
105
115
mV
Input Bias Current
0.3
3
A
Propagation Delay
150
ns
PWM COMPARATOR: I
SENSE
Input Offset Voltage
15
mV
Input Offset Current
1
A
Input Common Mode Range
0.2
5.5
V
Input Bias Current
2
10
A
Propagation Delay
150
ns
I
LIMIT
Trip Point
V
GM OUT
= 5.5V
4.8
5
5.2
V
OUTPUT
Output Voltage Low
I
OUT
= 20mA
0.1
0.4
V
I
OUT
= 200mA
1.6
2.2
V
Output Voltage High
I
OUT
= 20mA
13
13.5
V
I
OUT
= 200mA
12
13.4
V
Output Voltage Low in UVLO
I
OUT
= 5mA, V
CC
= 8V
0.1
0.8
V
Output Rise/Fall Time
C
L
= 1000pF
50
ns
Shutdown
V
IH
2.0
V
V
IL
0.8
V
I
IL
, V
SHDN
= 0V
1.5
mA
I
IH
, V
SHDN
= 5V
10
A
UNDER-VOLTAGE LOCKOUT
Startup Threshold
15
16
17
V
Shutdown Threshold
9
10
11
V
V
REF
Good Threshold
4.4
V
SUPPLY
Supply Current
Start-Up, V
CC
= 14V, T
J
= 25
C
0.8
1.2
mA
Operating, T
J
= 25
C
20
25
mA
Internal Shunt Zener 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: V
CC
is raised above the Startup Threshold first to activate the IC, then returned to 15V.
ML4812
REV. 1.0 10/10/2000
5
FUNCTIONAL DESCRIPTION
OSCILLATOR
The ML4812 oscillator charges the external capacitor (C
T
)
with a current (I
SET
) equal to 5/R
SET
. When the capacitor
voltage reaches the upper threshold, the comparator
changes state and the capacitor discharges to the lower
threshold through Q1. While the capacitor is discharging,
Q2 provides a high pulse.
The Oscillator period can be described by the following
relationship:
Figure 2. Oscillator Timing Resistance vs. Frequency
Figure 1. Oscillator Block Diagram
Figure 3. Output Saturation Voltage vs. Output Current
10
SYNC
Q
2
Q
1
9
RT
16
CT
EXTERNAL
CLOCK
+
-
5.6V
ISET
8.4mA
CT
RT
ISET
CSYNC
RSYNC
CLOCK
tD
RAMP VALLEY
RAMP PEAK
V(CT)
10
R
T
(k
)
OSCILLATOR FREQUENCY (kHz)
10
100
1000
8
5
3
2
1
MAXIMUM DUTY CYCLE (%)
10nF
20nF
5nF
2nF
1nF
85%
80%
70%
90%
15
14
13
3
2
1
0
OUTPUT SA
TURA
TION
V
O
L
T
A
GE (V)
OUTPUT CURRENT (mA)
0
200
400
800
600
VCC
VCC = 15V
80s PULSED LOAD
120Hz RATE
GND
SOURCE SATURATION
LOAD TO GROUND
SINK SATURATION
LOAD TO VCC
T
T
T
OSC
RAMP
DEADTIME
=
+
where:
V
V
D
OUT
IN
ON
=
-
1
and:
T
C
V
mA I
DEADTIME
T
RAMP VALLEY TO PEAK
SET
=
-
8 4
.
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