1
LT1248
Power Factor Controller
+
+
+
I
M
=
I
A
2
I
B
200
µ
A
2
V
CC
VA
OUT
16V TO 10V
2.6V/
2.2V
7.5V
7.9V
12
µ
A
5V
EA
V
REF
+
+
+
+
2.2V
32k
I
A
I
B
7
µ
A
I
M
7.5V
V
REF
+
+
0.7V
ONE SHOT
200ns
OSC
R
R
S
Q
C
SET
R
SET
13
6
11
8
10
7
9
5
4
3
2
1
15
16
12
14
SS
OVP
I
AC
V
SENSE
EN/SYNC
M
OUT
I
SENSE
CA
OUT
PK
LIM
V
CC
RUN
CA
RUN
1 6V
GND
+
GTDR
1248 BD
SYNC
M1
The LT
®
1248 provides active power factor correction for
universal off-line power systems. By using fixed high
frequency PWM current averaging, without the need for
slope compensation, the LT1248 achieves far lower line
current distortion with a smaller magnetic element than
systems that use either peak-current detection or zero
current switching approaches in both continuous and
discontinuous modes of operation.
The LT1248 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 LT1248 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 LT1248 provides many protection features including
peak current limiting and overvoltage protection, and can
be operated at frequencies as high as 300kHz.
s
High Power Factor Over Wide Load Range
with Line Current Averaging
s
International Operation Without Switches
s
Instantaneous Overvoltage Protection
s
Minimal Line Current Dead Zone
s
Typical 250
µ
A Start-Up Supply Current
s
Rejects Line Switching Noise
s
Synchronization Capability
s
Low Quiescent Current: 9mA
s
Fast 1.5A Peak Current Gate Driver
s
Universal Power Factor Corrected Power Supplies
s
Preregulators Up To 1500W
, LTC and LT are registered trademarks of Linear Technology Corporation.
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
BLOCK DIAGRA
W
2
LT1248
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
(Note 1)
Supply Voltage ....................................................... 27V
GTDR Current Continuous ..................................... 0.5A
GTDR Output Energy(Per Cycle) .............................. 5
µ
J
I
AC
, R
SET
, PK
LIM
Input Current ............................. 20mA
V
SENSE
, EN/SYNC, OVP Input Voltage ................... V
MAX
I
SENSE
, M
OUT
Input Current ..................................
±
5mA
Operating Junction Temperature Range
LT1248C ................................................ 0
°
C to 100
°
C
LT1248I ........................................... 40
°
C to 125
°
C
Thermal Resistance (Junction-to-Ambient)
N Package .................................................. 100
°
C/W
S Package ................................................... 120
°
C/W
Storage Temperature Range ..................65
°
C to 150
°
C
Lead Temperature (Soldering, 10 sec)................. 300
°
C
W
U
U
PACKAGE/ORDER I FOR ATIO
ELECTRICAL C
C
HARA TERISTICS
ORDER PART
NUMBER
The
q
denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at T
A
= 25
°
C. Maximum operating voltage (V
MAX
) = 25V, V
CC
= 18V, R
SET
= 15k to GND,
C
SET
= 1nF to GND, I
AC
= 100
µ
A, I
SENSE
= 0V, CA
OUT
= 3.5V, VA
OUT
= 5V, OVP = 7.5V, no load on any outputs, unless otherwise noted.
LT1248CN
LT1248IN
LT1248CS
LT1248IS
T
JMAX
= 125
°
C,
JA
= 100
°
C/W (N)
T
JMAX
= 125
°
C,
JA
= 120
°
C/W (S)
Consult factory for Military grade parts.
1
2
3
4
5
6
7
8
TOP VIEW
N PACKAGE
16-LEAD PDIP
S PACKAGE
16-LEAD NARROW PLASTIC SO
16
15
14
13
12
11
10
9
GND
PK
LIM
CA
OUT
I
SENSE
M
OUT
I
AC
VA
OUT
OVP
GTDR
V
CC
C
SET
SS
R
SET
V
SENSE
EN/SYNC
V
REF
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Overall
Supply Current (V
CC
in Undervoltage Lockout)
V
CC
= Lockout Voltage 0.2V
q
0.25
0.45
mA
Supply Current (Inactive)
EN/SYNC = 0V, V
CC
V
MAX
q
0.5
1.5
mA
Supply Current, On
11.5V
V
CC
V
MAX
, CA
OUT
= 1V
q
8.5
12.0
mA
V
CC
Turn-On Threshold (Undervoltage Lockout)
q
15.5
16.5
17.5
V
V
CC
Turn-Off Threshold
q
9.5
10.5
11.5
V
EN/SYNC Threshold, Rising
q
2.2
2.6
2.85
V
EN/SYNC Threshold Hysteresis
0.40
V
EN/SYNC Input Current
EN/SYNC = 0V
q
5
1
5
µ
A
3V
EN/SYNC
7V
50
25
50
µ
A
Voltage Amplifier
Voltage Amp Offset Voltage
VA
OUT
= 3.5V
q
8
8
mV
Input Bias Current
V
SENSE
= 0V to 7V
q
25
250
nA
Voltage Gain
70
100
dB
Voltage Amp Unity-Gain Bandwidth
3
MHz
Voltage Amp Output High (Internally Clamped)
q
11.3
13.3
V
Voltage Amp Output Low
q
1.1
2
V
Voltage Amp Short-Circuit Current
VA
OUT
= 0V
q
5
14
30
mA
SS Current
SS = 2.5V
q
5
12
30
µ
A
Current Amplifier
Current Amp Offset Voltage
q
±
1
±
4
mV
I
SENSE
Bias Current
q
25
250
nA
Current Amp Voltage Gain
80
110
dB
Current Amp Unity-Gain Bandwidth
3
MHz
Current Amp Output High
q
7.2
8.5
V
Current Amp Output Low
q
1.1
2
V
3
LT1248
I
M
I
AC
(VA
OUT
2)
2
Note 2: Multiplier Gain Constant: K =
ELECTRICAL C
C
HARA TERISTICS
The
q
denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at T
A
= 25
°
C. Maximum operating voltage (V
MAX
) = 25V, V
CC
= 18V, R
SET
= 15k to GND,
C
SET
= 1nF to GND, I
AC
= 100
µ
A, I
SENSE
= 0V, CA
OUT
= 3.5V, VA
OUT
= 5V, OVP = 7.5V, no load on any outputs, unless otherwise noted.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Current Amplifier
Current Amp Short-Circuit Current
CA
OUT
= 0V
q
5
14
30
mA
Input Range, I
SENSE
, M
OUT
(Linear Operation)
q
0.3
1
V
Reference
Reference Output Voltage
I
REF
= 0mA, T
A
= 25
°
C
7.39
7.50
7.60
V
V
REF
Load Regulation
5mA < I
REF
< 0mA
5
mV
V
REF
Line Regulation
11.5V < V
CC
< V
MAX
q
20
5
20
mV
V
REF
Short-Circuit Current
V
REF
= 0V
q
12
28
50
mA
V
REF
Worst Case
Load, Line, Temperature
q
7.32
7.5
7.68
V
Current Limit
PK
LIM
Offset Voltage
q
15
15
mV
PK
LIM
Input Current
PK
LIM
= 0.1V
q
50
100
µ
A
PK
LIM
to GTDR Propagation Delay
PK
LIM
Falling from 50mV to 50mV
400
ns
Multiplier
Multiplier Output Current
I
AC
= 100
µ
A, R
SET
= 15k
35
µ
A
Multiplier Output Current Offset
R
AC
= 1M from I
AC
to GND
q
0.05
0.5
µ
A
Multiplier Maximum Output Current
I
AC
= 450
µ
A, R
SET
= 15k, VA
OUT
= 7V, M
OUT
= 0V
q
286
260
235
µ
A
Multiplier Gain Constant (Note 2)
0.035
V
2
I
AC
Input Resistance
I
AC
from 50
µ
A to 1mA
15
32
50
k
Oscillator
Oscillator Frequency
R
SET
= 15k, C
SET
= 1000pF
q
85
100
115
kHz
R
SET
= 15k, C
SET
= 1500pF
q
58
68
78
kHz
C
SET
Ramp Peak-to-Peak Amplitude
4.35
4.7
5.0
V
C
SET
Ramp Valley Voltage
1.25
1.4
1.55
V
Synchronization Pulse Threshold on EN/SYNC Pin
Pulse Low = 3.5V, High = 7V, Width > 200ns
4.5
5.6
6.5
V
Synchronization Frequency Range
R
SET
= 15k, C
SET
= 1000pF
q
1.2
1.6
f
NOM
Overvoltage Comparator
Comparator Trip Voltage Ratio (V
TRIP
/ V
REF
)
q
1.04
1.05
1.06
Hysteresis
0.35
V
OVP Bias Current
OVP = 7.5V
q
50
250
nA
OVP Propagation Delay
100
ns
Gate Driver
Max GTDR Output Voltage
0mA Load, 18V < V
CC
q
12
15
17.5
V
GTDR Output High
200mA Load, 11.5V
V
CC
15V
q
V
CC
3.0
V
GTDR Output Low (Device Unpowered)
V
CC
= 0V, 50mA Load (Sinking)
q
0.9
1.5
V
GTDR Output Low (Device Active)
200mA Load (Sinking)
q
0.5
1
V
10mA Load
q
0.2
0.4
V
Peak GTDR Current
10nF from GTDR to GND
2
A
GTDR Rise and Fall Time
1nF from GTDR to GND
25
ns
GTDR Max Duty Cycle
90
96
%
4
LT1248
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Reference Voltage vs
Temperature
JUNCTION TEMPERATURE (
°
C)
75
REFERENCE VOLTAGE (V)
75
7.536
7.524
7.512
7.500
7.488
7.476
7.464
7.452
7.440
7.428
1248 G03
50
150
25
0
25
50
100 125
I
AC
(
µ
A)
0
I
M
(
µ
A)
300
150
0
1248 G04
250
500
VA
OUT
= 7V
VA
OUT
= 6.5V
VA
OUT
= 6V
VA
OUT
= 5.5V
VA
OUT
= 5V
VA
OUT
= 4.5V
VA
OUT
= 4V
VA
OUT
= 3.5V
VA
OUT
= 3V
VA
OUT
= 2.5V
SUPPLY VOLTAGE (V)
10
SUPPLY CURRENT (mA)
11
10
9
8
7
6
5
4
3
2
1
0
1248 G05
21
32
T
J
= 25
°
C
T
J
= 125
°
C
T
J
= 55
°
C
Supply Current vs Supply Voltage
GTDR Source Current
SINK CURRENT (mA)
0
GTDR VOLTAGE (V)
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1248 G07
300
T
A
= 125
°
C
T
A
= 55
°
C
60
120
180
240
T
A
= 25
°
C
FREQUENCY (Hz)
10
GAIN (dB)
100
80
60
40
20
0
20
100
1k
10k
100k
1148 G01
1M
10M
0
20
40
60
80
100
120
PHASE (DEG)
PHASE
GAIN
Voltage Amplifier Open-Loop
Gain and Phase
FREQUENCY (Hz)
10
GAIN (dB)
100
80
60
40
20
0
20
100
1k
10k
100k
1148 G02
1M
10M
0
20
40
60
80
100
120
PHASE (DEG)
PHASE
GAIN
Current Amplifier Open-Loop
Gain and Phase
Multiplier Current
SOURCE CURRENT (mA)
0
GTDR VOLTAGE (V)
18.5
18.0
17.5
17.0
16.5
16.0
15.5
15.0
14.5
14.0
13.5
13.0
1248 G06
300
T
J
= 25
°
C
T
J
= 125
°
C
V
CC
= 18V
T
J
= 55
°
C
60
120
180
240
GTDR Sink Current
5
LT1248
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
GTDR Rise and Fall Time
M
OUT
VOLTAGE (V)
M
OUT
CURRENT (mA)
1.5
1.0
0.5
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
1248 G15
2.4
1.2
0
1.2
2.4
T
J
= 125
°
C
T
J
= 25
°
C
T
J
= 55
°
C
Start-Up Supply Current vs
Supply Voltage
SUPPLY VOLTAGE (V)
0
SUPPLY CURRENT (
µ
A)
550
500
450
400
350
300
250
200
150
100
50
0
1248 G09
20
125
°
C
55
°
C
25
°
C
4
8
12
16
2
6
10
14
18
Frequency vs R
SET
and C
SET
Shutdown Mode Supply Current
and Reference Voltage
Synchronization and Shutdown
Thresholds at EN/SYNC Pin
C
SET
CAPACITANCE (pF)
200
FREQUENCY (kHz)
500
450
400
350
300
250
200
150
100
50
0
1248 G10
1400
2200
600
1000
1800
R
SET
= 10k
R
SET
= 15k
R
SET
= 20k
R
SET
= 30k
C
SET
CAPACITANCE (pF)
200
MAXIMUM DUTY CYCLE
1.00
0.99
0.98
0.97
0.96
0.95
0.94
0.93
0.92
0.91
0.90
1248 G11
1400
2200
600
1000
1800
R
SET
= 10k
R
SET
= 15k
R
SET
= 20k
R
SET
= 30k
EN/SYNC VOLTAGE (V)
0
EN/SYNC CURRENT (
µ
A)
44
40
36
32
28
24
20
16
12
8
4
0
1248 G13
10
5
T
J
= 125
°
C
1
2
3
4
6
7
8
9
T
J
= 25
°
C
T
J
= 55
°
C
SHUTDOWN
THRESHOLD
SYNCHRONIZATION
THRESHOLD
SS VOLTAGE (V)
0
SS CURRENT (
µ
A)
22
20
18
16
14
12
10
8
6
4
2
0
1248 G14
T
J
= 25
°
C
T
J
= 125
°
C
T
J
= 55
°
C
4
8
M
OUT
Pin Characteristics
SS Pin Characteristics
GTDR Maximum Duty Cycle vs
R
SET
and C
SET
LOAD CAPACITANCE (nF)
0
TIME (ns)
400
300
200
100
0
10
20
30
40
1248 G08
50
RISE TIME
NOTE: GTDR SLEWS
BETWEEN 1V AND 16V
FALL TIME
SUPPLY VOLTAGE (V)
0
SUPPLY CURRENT (mA)
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1248 G12
32
16
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
REFERENCE VOLTAGE (V)
EN/SYNC
1.8V
REFERENCE VOLTAGE
T
J
125
°
C
T
J
= 125
°
C
55
°
C
T
J
25
°
C
SUPPLY CURRENT
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