March 2001
PRELIMINARY
ML4801
Variable Feedforward PFC/PWM Controller Combo
GENERAL DESCRIPTION
The ML4801 is a controller for power factor corrected,
switched mode power supplies. Key features of this
combined PFC and PWM controller are low start-up and
operating currents. Power Factor Correction (PFC) allows
the use of smaller, lower cost bulk capacitors, reduces
power line loading and stress on the switching FETs, and
results in a power supply that fully complies with
IEC1000-2-3 specifications. The ML4801 includes circuits
for the implementation of a leading edge, average current
"boost" type power factor correction and a trailing edge
pulse width modulator (PWM).
The PFC frequency of the ML4801 is automatically set at
half that of the PWM frequency generated by the internal
oscillator. This technique allows the user to design with
smaller output components while maintaining the
optimum operating frequency for the PFC. An over-
voltage comparator shuts down the PFC section in the
event of a sudden decrease in load. The PFC section also
includes peak current limiting and input voltage brown-
out protection.
FEATURES
I
Internally synchronized PFC and PWM in one IC
I
Low start-up current (200
A typ.)
I
Low operating current (5.5mA typ.)
I
Low total harmonic distortion
I
Reduces ripple current in the storage capacitor
between the PFC and PWM sections
I
Average current continuous boost leading edge PFC
I
High efficiency trailing edge PWM optimized for
current mode operation
I
Current fed gain modulator for improved noise
immunity
I
Brown-out control, overvoltage protection, UVLO, and
soft start
BLOCK DIAGRAM
15
VEAO
IEAO
VFB
IAC
VRMS
ISENSE
RAMP 1
OSCILLATOR
OVP
PFC ILIMIT
UVLO
VREF
PULSE WIDTH MODULATOR
POWER FACTOR CORRECTOR
2.5V
+
-
-
+
16
2
4
3
7.5V
REFERENCE
14
VCC
13
VCC
VEA
8
+
IEA
1
+
-
+
-
PFC OUT
12
S
R
Q
Q
S
R
Q
Q
2.75V
-1V
RAMP 2
9
PWM OUT
11
GND
10
S
R
Q
Q
VDC
6
SS
5
RTCT
7
VCC
DUTY CYCLE
LIMIT
+
-
1.5V
-
+
2.5V
VFB
-
+
8V
8V
VIN OK
GAIN
MODULATOR
VCC
2
1.6k
1.6k
1.25V
25A
-
+
DC ILIMIT
REV. 1.1 3/9/2001
ML4801
2
REV. 1.1 3/9/2001
PIN CONFIGURATION
PIN DESCRIPTION
PIN
NAME
FUNCTION
9
RAMP 2
PWM ramp current sense input
10
GND
Ground
11
PWM OUT PWM driver output
12
PFC OUT
PFC driver output
13
V
CC
Positive supply (connected to an
internal shunt regulator).
14
V
REF
Buffered output for the internal 7.5V
reference
15
V
FB
PFC transconductance voltage error
amplifier input
16
VEAO
PFC transconductance voltage error
amplifier output
PIN
NAME
FUNCTION
1
IEAO
PFC transconductance current error
amplifier output
2
I
AC
PFC gain control reference input
3
I
SENSE
Current sense input to the PFC current
limit comparator
4
V
RMS
Input for PFC RMS line voltage
compensation
5
SS
Connection point for the PWM soft start
capacitor
6
V
DC
PWM voltage feedback input
7
R
T
C
T
Connection for oscillator frequency
setting components
8
RAMP 1
PFC ramp input
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
IEAO
IAC
ISENSE
VRMS
SS
VDC
RTCT
RAMP 1
VEAO
VFB
VREF
VCC
PFC OUT
PWM OUT
GND
RAMP 2
TOP VIEW
ML4801
16-Pin PDIP (P16)
16-Pin Narrow SOIC (S16N)
ML4801
REV. 1.1 3/9/2001
3
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, V
CC
= 15V, R
T
= 29.4k
, R
RAMP1
= 15.4k
, C
T
= 270pF, C
RAMP1
= 620pF,
T
A
= Operating Temperature Range (Note 1)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VOLTAGE ERROR AMPLIFIER
Input Voltage Range
0
5
V
Transconductance
V
NON INV
= V
INV
, VEAO = 3.75V
40
65
80
Feedback Reference Voltage
2.43
2.50
2.57
V
Input Bias Current
Note 2
-0.5
-1.0
A
Output High Voltage
6.0
6.7
V
Output Low Voltage
0.1
0.4
V
Source Current
V
IN
=
0.5V, V
OUT
= 6V
-40
-70
-150
A
Sink Current
V
IN
=
0.5V, V
OUT
= 1.5V
40
70
150
A
Open Loop Gain
60
70
dB
PSRR
11V < V
CC
< 16.5V
60
70
dB
CURRENT ERROR AMPLIFIER
Input Voltage Range
-1.5
2
V
Transconductance
V
NON INV
= V
INV
, VEAO = 3.75V
60
100
120
Input Offset Voltage
0
8
15
mV
Input Bias Current
-0.5
-1.0
A
Output High Voltage
6.0
6.7
V
Output Low Voltage
0.65
1.0
V
Source Current
V
IN
=
0.5V, V
OUT
= 6V
-40
-70
-150
A
Sink Current
V
IN
=
0.5V, V
OUT
= 1.5V
40
70
150
A
Open Loop Gain
55
65
dB
PSRR
11V < V
CC
< 16.5V
60
75
dB
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.
V
CC ..............................................................................................
18V
I
SENSE
Voltage .................................................. -3V to 5V
Voltage on Any Other Pin ...... GND - 0.3V to V
CC
+ 0.3V
I
REF ...........................................................................................
20mA
I
AC
Input Current ..................................................... 10mA
Peak PFC OUT Current, Source or Sink ................. 500mA
Peak PWM OUT Current, Source or Sink ............... 500mA
PFC OUT, PWM OUT Energy Per Cycle ................... 1.5
J
Junction Temperature ............................................. 150
C
Storage Temperature Range ...................... 65
C to 150C
Lead Temperature (Soldering, 10 sec) ..................... 260
C
Thermal Resistance (
JA
)
Plastic DIP ........................................................ 80
C/W
Plastic SOIC ................................................... 105
C/W
OPERATING CONDITIONS
Temperature Range
ML4801CX ................................................. 0
C to 70C
ML4801IX ............................................... -40
C to 85C
ML4801
4
REV. 1.1 3/9/2001
ELECTRICAL CHARACTERISTICS
(Continued)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
OVP COMPARATOR
Threshold Voltage
2.65
2.75
2.85
V
Hysteresis
175
250
325
mV
PFC I
LIMIT
COMPARATOR
Threshold Voltage
-0.9
-1.0
-1.1
V
PFC I
LIMIT
Threshold - Gain Modulator Output
120
220
mV
Delay to Output
150
300
ns
DC I
LIMIT
COMPARATOR
Threshold Voltage
1.4
1.5
1.6
V
Input Bias Current
0.3
1
A
Delay to Output
150
300
ns
V
IN
OK COMPARATOR
Threshold Voltage
2.4
2.5
2.6
V
Hysteresis
0.8
1.0
1.2
V
GAIN MODULATOR
Gain (Note 3)
I
AC
= 100
A, V
RMS
= V
FB
= 0V
0.65
0.85
1.05
I
AC
= 50
A, V
RMS
= 1V, V
FB
= 0V
1.90
2.20
2.40
I
AC
= 50
A, V
RMS
= 1.8V, V
FB
= 0V
0.90
1.05
1.25
I
AC
= 100
A, V
RMS
= 3.3V, V
FB
= 0V
0.20
0.30
0.40
Bandwidth
IAC = 100
A
10
MHz
Output Voltage
I
AC
= 350
A, V
RMS
= 1V,
0.65
0.75
0.85
V
V
FB
= 0V
OSCILLATOR
Initial Accuracy
T
A
= 25C
188
200
212
kHz
Voltage Stability
11V < V
CC
< 16.5V
1
%
Temperature Stability
2
%
Total Variation
Over Line and Temp
182
218
kHz
Ramp Valley to Peak Voltage
2.5
V
PFC Dead Time
350
470
600
ns
C
T
Discharge Current
V
RAMP 2
= 0V, V
RAMP 1
= 2.5V
3.5
5.5
7.5
mA
ML4801
REV. 1.1 3/9/2001
5
ELECTRICAL CHARACTERISTICS
(Continued)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
REFERENCE
Output Voltage
T
A
= 25C, I(V
REF
) = 1mA
7.4
7.5
7.6
V
Line Regulation
11V < V
CC
< 16.5V
10
25
mV
Load Regulation
1mA < I(V
REF
) < 10mA
10
20
mV
Temperature Stability
0.4
%
Total Variation
Line, Load, Temp
7.35
7.65
V
Long Term Stability
T
J
= 125C, 1000 Hours
5
25
mV
PFC
Minimum Duty Cycle
V
IEAO
> 6.7V
0
%
Maximum Duty Cycle
V
IEAO
< 1.2V
90
95
%
Output Low Voltage
I
OUT
= -20mA
0.4
0.8
V
I
OUT
= -100mA
0.7
2.0
V
I
OUT
= -10mA, V
CC
= 9V
0.4
0.8
V
Output High Voltage
I
OUT
= 20mA
V
CC
- 0.8
V
I
OUT
= 100mA
V
CC
- 2.0
V
Rise/Fall Time
C
L
= 1000pF
50
ns
PWM
DC
Duty Cycle Range
0-44
0-47
0-50
%
V
OL
Output Low Voltage
I
OUT
= -20mA
0.4
0.8
V
I
OUT
= -100mA
0.7
2.0
V
I
OUT
= -10mA, V
CC
= 9V
0.4
0.8
V
V
OH
Output High Voltage
I
OUT
= 20mA
V
CC
- 0. 8
V
I
OUT
= 100mA
V
CC
- 2.0
V
Rise/Fall Time
C
L
= 1000pF
50
ns
SUPPLY
Start-up Current
V
CC
= 12V, C
L
= 0
200
350
A
Operating Current
V
CC
= 14V, C
L
= 0
5.5
7.0
mA
Undervoltage Lockout Threshold
12.4
13.0
13.6
V
Undervoltage Lockout Hysteresis
2.7
3.0
3.3
V
Note 1: Limits are guaranteed by 100% testing, sampling, or correlation with worst-case test conditions.
Note 2: Includes all bias currents to other circuits connected to the V
FB
pin.
Note 3: Gain = K x 5.3V; K = (I
MULO
- I
OFFSET
) x I
AC
x (VEAO - 0.625V)
-1
.
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