November 1998
PRELIMINARY
ML4805
Variable Feedforward PFC/PWM Controller Combo
GENERAL DESCRIPTION
The ML4805 is a controller for power factor corrected,
switched mode power supplies. Similar to the ML4801,
the ML4805 may be used for voltage mode operation. 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
ML4805 includes circuits for the implementation of a
leading edge, average current “boost” type power factor
correction and a trailing edge pulse width modulator.
The PFC frequency of the ML4805 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
I
I
I
I
Internally synchronized PFC and PWM in one IC
Low start-up current (200µA typ.)
Low operating current (5.5mA typ.)
Low total harmonic distortion
Reduces ripple current in the storage capacitor
between the PFC and PWM sections
Average current continuous boost leading edge PFC
High efficiency trailing edge PWM optimized for
voltage mode operation
Current fed gain modulator for improved noise
immunity
Brown-out control, overvoltage protection, UVLO, and
soft start
I
I
I
I
BLOCK DIAGRAM
18
VEAO
VFB
17
2.5V
IAC
2
VRMS
4
ISENSE
3
RAMP 1
8
RTCT
7
RAMP 2
9
8V
VDC
6
VCC
SS
5
AGND
11
PULSE WIDTH MODULATOR
VCC
UVLO
8V
25µA
1.25V
-
+
-
+
-
+
1
IEAO
POWER FACTOR CORRECTOR
OVP
1.6kΩ
+
–
15
VCC
VCC
7.5V
REFERENCE
S
-1V
+
-
+
+
-
VEA
VREF
16
IEA
2.75V
-
Q
GAIN
MODULATOR
1.6kΩ
R
S
Q
PFC OUT
Q
14
PFC ILIMIT
R
Q
OSCILLATOR
÷2
PGND
DUTY CYCLE
LIMIT
12
PWM OUT
VIN OK
VFB
2.5V
-
+
+
S
Q
13
R
DC ILIMIT
Q
ILIM
10
1.5V
-
REV. 1.1 3/9/2001
ML4805
PIN CONFIGURATION
ML4805
18-Pin PDIP (P18)
18-Pin SOIC (S18)
IEAO
IAC
ISENSE
VRMS
SS
VDC
RTCT
RAMP 1
RAMP 2
1
2
3
4
5
6
7
8
9
18
17
16
15
14
13
12
11
10
VEAO
VFB
VREF
VCC
PFC OUT
PWM OUT
PGND
AGND
ILIM
TOP VIEW
PIN DESCRIPTION
PIN
NAME
FUNCTION
PIN
NAME
FUNCTION
1
2
3
4
5
6
7
8
IEAO
I
AC
I
SENSE
V
RMS
SS
V
DC
R
T
C
T
RAMP 1
PFC transconductance current error
amplifier output
PFC gain control reference input
9
10
11
RAMP 2
ILIM
AGND
PGND
PWM ramp sense input
PWM current limit sense input
Analog ground
Power ground
Current sense input to the PFC current
limit comparator
Input for PFC RMS line voltage
compensation
Connection point for the PWM soft start
capacitor
PWM voltage feedback input
12
13
14
15
16
PWM OUT PWM driver output
PFC OUT
V
CC
V
REF
V
FB
VEAO
PFC driver output
Positive supply (connected to an
internal shunt regulator).
Buffered output for the internal 7.5V
reference
PFC transconductance voltage error
amplifier input
PFC transconductance voltage error
amplifier output
Connection for oscillator frequency
setting components
17
PFC ramp input
18
2
REV. 1.1 3/9/2001
ML4805
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 ................... 1.5µJ
Junction Temperature ............................................. 150°C
Storage Temperature Range ...................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ..................... 260°C
Thermal Resistance (θ
JA
)
Plastic DIP ........................................................ 70°C/W
Plastic SOIC ................................................... 100°C/W
OPERATING CONDITIONS
Temperature Range
ML4805CX ................................................. 0°C to 70°C
ML4805IX ............................................... -40°C to 85°C
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, V
CC
= 15V, R
T
= 29.4kΩ, R
RAMP1
= 15.4kΩ, 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
Transconductance
Feedback Reference Voltage
Input Bias Current
Output High Voltage
Output Low Voltage
Source Current
Sink Current
Open Loop Gain
PSRR
CURRENT ERROR AMPLIFIER
Input Voltage Range
Transconductance
Input Offset Voltage
Input Bias Current
Output High Voltage
Output Low Voltage
Source Current
Sink Current
Open Loop Gain
PSRR
11V < V
CC
< 16.5V
∆V
IN
=
±0.5V,
V
OUT
= 6V
∆V
IN
=
±0.5V,
V
OUT
= 1.5V
-40
40
55
60
6.0
V
NON INV
= V
INV
, VEAO = 3.75V
-1.5
60
0
100
8
-0.5
6.7
0.65
-70
70
65
75
1.0
-150
150
2
120
15
-1.0
V
11V < V
CC
< 16.5V
∆V
IN
=
±0.5V,
V
OUT
= 6V
∆V
IN
=
±0.5V,
V
OUT
= 1.5V
-40
40
60
60
Note 2
6.0
V
NON INV
= V
INV
, VEAO = 3.75V
0
40
2.43
65
2.50
-0.5
6.7
0.1
-70
70
70
70
0.4
-150
150
5
80
2.57
-1.0
V
V
µA
V
V
µA
µA
dB
dB
mV
µA
V
V
µA
µA
dB
dB
REV. 1.1 3/9/2001
Ω
µ
Ω
µ
3
ML4805
ELECTRICAL CHARACTERISTICS
(Continued)
SYMBOL
OVP COMPARATOR
Threshold Voltage
Hysteresis
PFC I
LIMIT
COMPARATOR
Threshold Voltage
∆PFC
I
LIMIT
Threshold - Gain Modulator Output
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
2.65
175
2.75
250
2.85
325
V
mV
-0.9
120
-1.0
220
150
-1.1
V
mV
Delay to Output
DC I
LIMIT
COMPARATOR
Threshold Voltage
Input Bias Current
Delay to Output
V
IN
OK COMPARATOR
Threshold Voltage
Hysteresis
GAIN MODULATOR
Gain (Note 3)
I
AC
= 100µA, V
RMS
= V
FB
= 0V
I
AC
= 50µA, V
RMS
= 1V, V
FB
= 0V
I
AC
= 50µA, V
RMS
= 1.8V, V
FB
= 0V
I
AC
= 100µA, V
RMS
= 3.3V, V
FB
= 0V
Bandwidth
Output Voltage
OSCILLATOR
Initial Accuracy
Voltage Stability
Temperature Stability
Total Variation
Ramp Valley to Peak Voltage
PFC Dead Time
C
T
Discharge Current
V
RAMP 2
= 0V, V
RAMP 1
= 2.5V
350
3.5
Line, Temp
182
T
A
= 25ºC
11V < V
CC
< 16.5V
188
IAC = 100µA
I
AC
= 350µA, V
RMS
= 1V,
V
FB
= 0V
0.65
0.65
1.90
0.90
0.20
2.4
0.8
1.4
300
ns
1.5
±0.3
150
1.6
±1
300
V
µA
ns
2.5
1.0
2.6
1.2
V
V
0.85
2.20
1.05
0.30
10
0.75
1.05
2.40
1.25
0.40
MHz
0.85
V
200
1
2
212
kHz
%
%
218
2.5
470
5.5
600
7.5
kHz
V
ns
mA
4
REV. 1.1 3/9/2001
ML4805
ELECTRICAL CHARACTERISTICS
(Continued)
SYMBOL
REFERENCE
Output Voltage
Line Regulation
Load Regulation
Temperature Stability
Total Variation
Long Term Stability
PFC
Minimum Duty Cycle
Maximum Duty Cycle
Output Low Voltage
V
IEAO
> 6.7V
V
IEAO
< 1.2V
I
OUT
= -20mA
I
OUT
= -100mA
I
OUT
= -10mA, V
CC
= 9V
Output High Voltage
I
OUT
= 20mA
I
OUT
= 100mA
Rise/Fall Time
PWM
DC
V
OL
Duty Cycle Range
Output Low Voltage
I
OUT
= -20mA
I
OUT
= -100mA
I
OUT
= -10mA, V
CC
= 9V
V
OH
Output High Voltage
I
OUT
= 20mA
I
OUT
= 100mA
Rise/Fall Time
SUPPLY
Start-up Current
Operating Current
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
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
.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
T
A
= 25ºC, I(V
REF
) = 1mA
11V < V
CC
< 16.5V
1mA < I(V
REF
) < 10mA
7.4
7.5
10
10
0.4
7.6
25
20
V
mV
mV
%
Line, Load, Temp
T
J
= 125ºC, 1000 Hours
7.35
5
7.65
25
V
mV
0
90
95
0.4
0.7
0.4
V
CC
- 0.8
V
CC
- 2.0
50
0.8
2.0
0.8
%
%
V
V
V
V
V
ns
C
L
= 1000pF
0-44
0-47
0.4
0.7
0.4
0-50
0.8
2.0
0.8
%
V
V
V
V
V
V
CC
- 0. 8
V
CC
- 2.0
50
C
L
= 1000pF
ns
V
CC
= 12V, C
L
= 0
V
CC
= 14V, C
L
= 0
12.4
2.7
200
5.5
13.0
3.0
350
7.0
13.6
3.3
µA
mA
V
V
REV. 1.1 3/9/2001
5
Analog electronics
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