LT1249
Power Factor Controller
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
Standard 8-Pin Packages
High Power Factor Over Wide Load Range
with Line Current Averaging
International Operation Without Switches
Instantaneous Overvoltage Protection
Minimal Line Current Dead Zone
Typical 250µA Start-Up Supply Current
Rejects Line Switching Noise
Synchronization Capability
Low Quiescent Current: 9mA
Fast 1.5A Peak Current Gate Driver
The 8-pin LT
®
1249 provides active power factor correc-
tion for universal offline power systems with very few
external parts. By using fixed high frequency PWM current
averaging without the need for slope compensation, the
LT1249 achieves far lower line current distortion, with a
smaller magnetic element than systems that use either peak
current detection or zero current switching approach, in
both continuous and discontinuous modes of operation.
The LT1249 uses a multiplier containing a square gain
function from the voltage amplifier to reduce the AC gain
at light output load and thus maintains low line current
distortion and high system stability. The LT1249 also
provides filtering capability to reject line switching noise
which can cause instability when fed into the multiplier.
Line current dead zone is minimized with low bias voltage
at the current input to the multiplier.
The LT1249 provides many protection features including
peak current limiting and overvoltage protection. The
switching frequency is internally set at 100kHz.
While the LT1249 simplifies PFC design with minimal
parts count, the LT1248 provides flexibilities in switching
frequency, overvoltage and current limit.
APPLICATIO S
s
s
Universal Power Factor Corrected Power Supplies
Preregulators up to 1500W
, LTC and LT are registered trademarks of Linear Technology Corporation.
BLOCK DIAGRA
VA
OUT
5
V
SENSE
7.5V
6
I
AC
4
+
M
OUT
3
R
MOUT
4k
I
A
I
B
32k
MULTIPLIER
I I
I
M
=
A B
2
200µA
15µA
1V
+
2
CA
OUT
2
EA
–
V
CC
16V/10V
+
–
–
I
M
250µA MAX
+
CA
–
+
+
g
m
= 1/3k
RUN
0.7V
M1
–
+
SYNC
OSC
20µA
35pF
1249 BD
44µA
22µA
4k
–
U
GND
1
7.5V
V
REF
RUN
V
CC
7
R
S
Q
GTDR
8
16V
W
U
1
LT1249
ABSOLUTE
MAXIMUM
RATINGS
Supply Voltage ....................................................... 27V
GTDR Current Continuous ..................................... 0.5A
GTDR Output Energy (Per Cycle) ............................. 5µJ
I
AC
Input Current ................................................. 20mA
V
SENSE
Input Voltage ............................................ V
MAX
M
OUT
Input Current..............................................
±
5mA
Operating Junction Temperature Range
LT1249C ................................................ 0°C to 100°C
LT1249I ........................................... – 40°C to 125°C
Thermal Resistance (Junction-to-Ambient)
N8 Package ................................................ 100°C/W
S8 Package ................................................. 120°C/W
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
GND 1
CA
OUT
2
M
OUT
3
I
AC
4
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 100°C/W (N8)
T
JMAX
= 125°C,
θ
JA
= 120°C/W (S8)
ORDER PART
NUMBER
8
7
6
5
GTDR
V
CC
V
SENSE
VA
OUT
LT1249CN8
LT1249IN8
LT1249CS8
LT1249IS8
S8 PART
MARKING
1249
1249I
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Overall
Supply Current (V
CC
in Undervoltage Lockout)
Supply Current, On
V
CC
Turn-On Threshold
V
CC
Turn-Off Threshold
Voltage Amplifier
V
SENSE
Bias Current
Voltage Amp Gain
Voltage Amp Unity-Gain Bandwidth
Voltage Amp Output High
Voltage Amp Output Low
Voltage Amp Source Current
Voltage Amp Sink Current Threshold
Voltage Amp Sink Current Hysteresis
Current Amplifier
Current Amp Offset Voltage
Current Amp Transconductance
Current Amp Voltage Gain
Current Amp Source Current
Current Amp Sink Current
Current Amp Output High
Current Amp Output Low
The
q
denotes specifications which apply over the operating temperature
range, otherwise specifications are at T
A
= 25°C. Maximum operating voltage (V
MAX
) = 25V, V
CC
= 18V, I
AC
= 100µA, CA
OUT
= 3.5V,
VA
OUT
= 5V, no load on any outputs, unless otherwise noted.
CONDITIONS
V
CC
= Lockout Voltage – 0.2V
11.5V
≤
V
CC
≤
V
MAX
, CA
OUT
= 1V
q
q
q
q
MIN
TYP
0.25
9
16.5
10.5
–25
100
1.5
12
0.1
260
44
22.5
±2
320
1000
145
95
8.1
1.2
MAX
0.45
12
17.5
11.5
–250
UNITS
mA
mA
V
V
nA
dB
MHz
V
V
µA
µA
µA
mV
µmho
V/V
µA
µA
V
V
15.5
9.5
V
SENSE
= 0V to 7V
q
70
0
≤
Source Current
≤
50µA
0
≤
Sink Current
≤
5µA
Linear Operation, 2V < VA
OUT
< 10V
2V < VA
OUT
< 10V
q
q
q
q
q
q
10
130
33
14
0.4
450
57
30
±15
550
220
125
2
∆I
CAOUT
=
±40µA
2.5V
≤
V
CAOUT
≤
7.5V
V
MOUT
= 1V, I
M
= 0µA
V
MOUT
= – 0.3V, I
M
= 0µA
q
150
500
100
67
7.4
2
U
W
U
U
W W
W
LT1249
ELECTRICAL CHARACTERISTICS
PARAMETER
Reference
Reference Output Voltage
Reference Output Voltage Worst Case
Reference Output Voltage Line Regulation
Multiplier
Multiplier Output Current
Multiplier Output Current Offset
Multiplier Max Output Current (I
M(MAX)
)
Multiplier Max Output Voltage (I
M(MAX)
• R
MOUT
)
Multiplier Gain Constant (Note 3)
I
AC
Input Resistance
Oscillator
Oscillator Frequency
Control Pin (CA
OUT
) Threshold
Synchronization Frequency Range
Gate Driver
Max GTDR Output Voltage
GTDR Output High
GTDR Output Low (Device Unpowered)
GTDR Output Low (Device Active)
Peak GTDR Current
GTDR Rise and Fall Time
GTDR Max Duty Cycle
The
q
denotes specifications which apply over the operating temperature
range, otherwise specifications are at T
A
= 25°C. Maximum operating voltage (V
MAX
) = 25V, V
CC
= 18V, I
AC
= 100µA, CA
OUT
= 3.5V,
VA
OUT
= 5V, no load on any outputs, unless otherwise noted.
CONDITIONS
T
A
= 25°C, Measured at V
SENSE
Pin
All Line, Temperature
V
LOCKOUT
< V
CC
< V
MAX
I
AC
= 100µA, VA
OUT
= 5V
R
AC
= 1M from I
AC
to GND
I
AC
= 450µA, VA
OUT
= 7V (Note 2)
I
AC
= 450µA, VA
OUT
= 7V (Note 2)
I
AC
from 50µA to 1mA
q
MIN
7.39
7.32
– 20
TYP
7.5
7.5
5
35
– 0.05
– 250
– 1.1
0.035
32
100
1.8
MAX
7.6
7.68
20
UNITS
V
V
mV
µA
µA
µA
V
V
–2
kΩ
kHz
V
kHz
V
V
V
V
A
ns
%
q
q
q
q
q
– 375
– 1.25
15
75
1.3
127
12
V
CC
– 3.0
– 0.5
– 150
– 0.96
50
125
2.3
160
17.5
1.5
1
Duty Cycle = 0
Synchronizing Pulse Low
≤
0.35V on CA
OUT
0mA Load, 18V < V
CC
< V
MAX
(Note 4)
– 200mA Load, 11.5V
≤
V
CC
≤
15V
V
CC
= 0V, 50mA Load (Sinking)
200mA Load (Sinking)
10nF from GTDR to GND
1nF from GTDR to GND
q
q
q
q
q
q
15
0.9
0.5
1.5
25
96
I
M
90
Note 3:
Multiplier Gain Constant: K =
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Current amplifier is in linear mode with 0V input common mode.
I
AC
(VA
OUT
– 1.5)
2
Note 4:
Maximum GTDR output voltage is internally clamped for higher
V
CC
voltages.
TYPICAL PERFORMANCE CHARACTERISTICS
Voltage Amplifier Open-Loop
Gain and Phase
100
80
GAIN
60
GAIN (dB)
TRANSCONDUCTANCE (µmho)
40
20
0
–20
PHASE
10
100
1k
10k 100k
FREQUENCY (Hz)
U W
Transconductance of
Current Amplifier
0
–20
–40
–60
–80
–100
–120
10M
1249 G01
1249 G02
400
350
300
250
200
150
100
50
0
1k
10k
1M
100k
FREQUENCY (Hz)
θ
g
m
20
0
–20
PHASE (DEG)
–40
–60
–80
PHASE (DEG)
–100
–120
–140
10M
1M
3
LT1249
TYPICAL PERFORMANCE CHARACTERISTICS
Reference Voltage vs
Temperature
7.536
7.524
REFERENCE VOLTAGE (V)
300
VA
OUT
= 6.5V
VA
OUT
= 6V
VA
OUT
= 5.5V
VA
OUT
= 4.5V
VA
OUT
= 4V
VA
OUT
= 3.5V
VA
OUT
= 3V
0
VA
OUT
= 2.5V
VA
OUT
= 2V
500
1249 G04
7.512
7.500
7.488
7.476
7.464
7.452
7.440
7.428
–75 –50 –25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (°C)
1249 G03
I
M
(µA)
Supply Current vs Supply Voltage
10
9
8
T
J
= –55°C
T
J
= 25°C
SUPPLY CURRENT (mA)
GTDR VOLTAGE (V)
T
J
= 125°C
6
5
4
3
2
1
0
10 12 14 16 18 20 22 24 26 28 30
SUPPLY VOLTAGE (V)
1249 G05
16.5
16.0
15.5
15.0
14.5
14.0
13.5
13.0
0
–120
–180
–240
– 60
SOURCE CURRENT (mA)
–300
1249 G06
GTDR VOLTAGE (V)
7
GTDR Rise and Fall Time
400
550
500
450
SUPPLY CURRENT (µA)
300
TIME (ns)
350
300
250
200
150
100
50
0
–55°C
25°C
125°C
FREQUENCY (kHz)
FALL TIME
200
RISE TIME
100
NOTE: GTDR SLEWS
BETWEEN 1V AND 16V
0
0
10
20
30
40
LOAD CAPACITANCE (nF)
50
1249 G08
4
U W
Multiplier Current
VA
OUT
= 5V
150
0
250
I
AC
(µA)
GTDR Source Current
18.5
18.0
17.5
17.0
V
CC
= 18V
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
GTDR Sink Current
T
J
= 125°C
T
J
= 25°C
T
J
= –55°C
T
A
= –55°C
T
A
= 25°C
T
A
= 125°C
0
60
120
180
240
SINK CURRENT (mA)
300
1249 G07
Start-Up Supply Current vs
Supply Voltage
140
130
120
110
100
90
80
Switching Frequency
400
0
2
4
6 8 10 12 14 16 18 20
SUPPLY VOLTAGE (V)
1249 G09
70
25 50 75
–75 –50 –25 0
TEMPERATURE (°C)
100 125
1249 G10
LT1249
TYPICAL PERFORMANCE CHARACTERISTICS
Synchronization Threshold
at CA
OUT
1.0
1.2
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–25
0
25
50
75
TEMPERATURE (°C)
100
125
–1.0
–2.4
0
–1.2
1.2
M
OUT
VOLTAGE (V)
2.4
1249 G12
SYNCHRONIZATION THRESHOLD (V)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
–50
TRANSCONDUCTANCE (µmho)
M
OUT
CURRENT (mA)
Voltage Amp Sink Current Limits
(Threshold)
60
50
UP THRESHOLD
I
M(MAX)
×
R
MOUT
(V)
40
30
DOWN THRESHOLD
20
10
0
–75 –50
–1.15
–1.10
–1.05
–1.00
–0.95
DUTY CYCLE (%)
CURRENT (µA)
–25 0
25 50 75
TEMPERATURE (°C)
NOTE: THESE SINK CURRENT THRESHOLDS ARE
FOR OVERVOLTAGE PROTECTION FUNCTION.
PIN FUNCTIONS
GND (Pin 1):
Ground.
CA
OUT
(Pin 2):
This is the output of the current amplifier
that senses and forces the line current to follow the
reference signal that comes from the multiplier by com-
manding the pulse width modulator. When CA
OUT
is low,
the modulator has zero duty cycle.
M
OUT
(Pin 3):
The multiplier current goes out of this pin
through the 4k resistor R
MOUT
. The voltage developed
across R
MOUT
is the reference voltage of the current loop
and it is limited to 1.1V. The noninverting input of the
current amplifier is also tied to R
MOUT
. In operation, M
OUT
is normally at negative potential and only AC signals
appear at the noninverting input of the current amplifier.
I
AC
(Pin 4):
This is the AC line voltage sensing input to the
multiplier. It is a current input that is biased at 2V to
minimize the crossover dead zone caused by low line
voltage. A 32k resistor is in series with the current input,
so that a small external capacitor can be used to filter out
the switching noise from the high impedance lines.
VA
OUT
(Pin 5):
This is the output of the voltage error
amplifier. The output is clamped at 12V. When the output
goes below 1.5V, the multiplier output current is zero.
U W
1249 G11
M
OUT
Pin Characteristics
400
125°C
25°C
–50°C
350
300
250
200
150
100
50
Transconductance of Current
Amplifier Over Temperature
0
–50 –25
0
25
50
75
100
125
TEMPERATURE (°C)
1249 G13
Maximum Multiplier Output
Voltage (I
M(MAX)
• R
MOUT
)
–1.30
–1.25
–1.20
Maximum Duty Cycle
100
99
98
97
96
95
94
93
92
91
100 125
–0.90
–75 –50
–25
0
25
50
75
100 125
1249 G15
90
–50
–25
TEMPERATURE (°C)
1249 G14
0
25
50
75
TEMPERATURE (°C)
100
125
1249 G16
U
U
U
5
