LT1248
Power Factor Controller
U
GND
1
–
+
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTIO
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 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
Universal Power Factor Corrected Power Supplies
Preregulators Up To 1500W
BLOCK DIAGRA
V
CC
16V TO 10V
EN/SYNC
10
V
SENSE
11
I
AC
6
OVP
8
7.9V
7.5V
2.6V/
2.2V
+
–
–
+
–
EA
+
+
–
–
SS
13
12µA
5V
+
ONE SHOT
200ns
–
+
W
U
VA
OUT
7
V
REF
9
7.5V
V
REF
RUN
M
OUT
I
SENSE
5
4
CA
OUT
PK
LIM
3
2
V
CC
15
2.2V
7µA
+
M1
–
I
A
32k
I I
I =
A B
I
B M
200µA
2
2
I
M
–
CA
+
–
+
R
R
RUN
S
Q
16
GTDR
0.7V
SYNC
OSC
1 6V
14
C
SET
12
R
SET
1248 BD
1
LT1248
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
GND
PK
LIM
CA
OUT
I
SENSE
M
OUT
I
AC
VA
OUT
OVP
1
2
3
4
5
6
7
8
16 GTDR
15 V
CC
14 C
SET
13 SS
12 R
SET
11 V
SENSE
10 EN/SYNC
9
V
REF
Supply Voltage ....................................................... 27V
GTDR Current Continuous ..................................... 0.5A
GTDR Output Energy(Per Cycle) .............................. 5µJ
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
ORDER PART
NUMBER
LT1248CN
LT1248IN
LT1248CS
LT1248IS
N PACKAGE
16-LEAD PDIP
S PACKAGE
16-LEAD NARROW PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 100°C/W (N)
T
JMAX
= 125°C,
θ
JA
= 120°C/W (S)
Consult factory for Military grade parts.
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
= 100µA, I
SENSE
= 0V, CA
OUT
= 3.5V, VA
OUT
= 5V, OVP = 7.5V, no load on any outputs, unless otherwise noted.
PARAMETER
Overall
Supply Current (V
CC
in Undervoltage Lockout)
Supply Current (Inactive)
Supply Current, On
V
CC
Turn-On Threshold (Undervoltage Lockout)
V
CC
Turn-Off Threshold
EN/SYNC Threshold, Rising
EN/SYNC Threshold Hysteresis
EN/SYNC Input Current
Voltage Amplifier
Voltage Amp Offset Voltage
Input Bias Current
Voltage Gain
Voltage Amp Unity-Gain Bandwidth
Voltage Amp Output High (Internally Clamped)
Voltage Amp Output Low
Voltage Amp Short-Circuit Current
SS Current
Current Amplifier
Current Amp Offset Voltage
I
SENSE
Bias Current
Current Amp Voltage Gain
Current Amp Unity-Gain Bandwidth
Current Amp Output High
Current Amp Output Low
CONDITIONS
V
CC
= Lockout Voltage – 0.2V
EN/SYNC = 0V, V
CC
≤
V
MAX
11.5V
≤
V
CC
≤
V
MAX
, CA
OUT
= 1V
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
MIN
TYP
0.25
0.5
8.5
16.5
10.5
2.6
0.40
–1
– 25
MAX
0.45
1.5
12.0
17.5
11.5
2.85
5
50
8
– 250
UNITS
mA
mA
mA
V
V
V
V
µA
µA
mV
nA
dB
MHz
V
V
mA
µA
mV
nA
dB
MHz
V
V
15.5
9.5
2.2
–5
– 50
–8
70
EN/SYNC = 0V
3V
≤
EN/SYNC
≤
7V
VA
OUT
= 3.5V
V
SENSE
= 0V to 7V
q
q
q
q
q
11.3
5
5
VA
OUT
= 0V
SS = 2.5V
q
q
q
q
– 25
100
3
13.3
1.1
14
12
±1
– 25
110
3
8.5
1.1
2
30
30
±4
– 250
80
q
q
7.2
2
2
U
W
U
U
W W
W
LT1248
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
= 100µA, I
SENSE
= 0V, CA
OUT
= 3.5V, VA
OUT
= 5V, OVP = 7.5V, no load on any outputs, unless otherwise noted.
PARAMETER
Current Amplifier
Current Amp Short-Circuit Current
Input Range, I
SENSE
, M
OUT
(Linear Operation)
Reference
Reference Output Voltage
V
REF
Load Regulation
V
REF
Line Regulation
V
REF
Short-Circuit Current
V
REF
Worst Case
Current Limit
PK
LIM
Offset Voltage
PK
LIM
Input Current
PK
LIM
to GTDR Propagation Delay
Multiplier
Multiplier Output Current
Multiplier Output Current Offset
Multiplier Maximum Output Current
Multiplier Gain Constant (Note 2)
I
AC
Input Resistance
Oscillator
Oscillator Frequency
C
SET
Ramp Peak-to-Peak Amplitude
C
SET
Ramp Valley Voltage
Synchronization Pulse Threshold on EN/SYNC Pin
Synchronization Frequency Range
Overvoltage Comparator
Comparator Trip Voltage Ratio (V
TRIP
/ V
REF
)
Hysteresis
OVP Bias Current
OVP Propagation Delay
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
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired
I
M
Note 2:
Multiplier Gain Constant: K =
I
AC
(VA
OUT
– 2)
2
0mA Load, 18V < V
CC
– 200mA Load, 11.5V
≤
V
CC
≤
15V
V
CC
= 0V, 50mA Load (Sinking)
200mA Load (Sinking)
10mA Load
10nF from GTDR to GND
1nF from GTDR to GND
90
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
CA
OUT
= 0V
q
q
MIN
5
– 0.3
7.39
q
q
q
TYP
14
MAX
30
1
UNITS
mA
V
V
mV
mV
mA
V
mV
µA
ns
µA
I
REF
= 0mA, T
A
= 25°C
– 5mA < I
REF
< 0mA
11.5V < V
CC
< V
MAX
V
REF
= 0V
Load, Line, Temperature
7.50
5
5
28
7.5
7.60
20
50
7.68
15
– 20
12
7.32
– 15
PK
LIM
= – 0.1V
PK
LIM
Falling from 50mV to – 50mV
I
AC
= 100µA, R
SET
= 15k
R
AC
= 1M from I
AC
to GND
I
AC
= 450µA, R
SET
= 15k, VA
OUT
= 7V, M
OUT
= 0V
I
AC
from 50µA to 1mA
R
SET
= 15k, C
SET
= 1000pF
R
SET
= 15k, C
SET
= 1500pF
q
– 50
400
35
– 100
q
q
– 0.05
– 286
15
– 260
0.035
32
100
68
4.7
1.4
5.6
– 0.5
– 235
50
115
78
5.0
1.55
6.5
1.6
µA
µA
V
–2
kΩ
kHz
kHz
V
V
V
f
NOM
q
q
85
58
4.35
1.25
Pulse Low = 3.5V, High = 7V, Width > 200ns
R
SET
= 15k, C
SET
= 1000pF
4.5
q
1.2
1.04
1.05
0.35
– 50
100
12
V
CC
– 3.0
0.9
0.5
0.2
2
25
96
15
1.06
V
– 250
nA
ns
17.5
1.5
1
0.4
V
V
V
V
V
A
ns
%
OVP = 7.5V
q
3
LT1248
TYPICAL PERFOR A CE CHARACTERISTICS
Voltage Amplifier Open-Loop
Gain and Phase
100
80
GAIN
60
GAIN (dB)
40
20
0
–20
–60
–80
GAIN (dB)
PHASE
10
100
1k
10k 100k
FREQUENCY (Hz)
Reference Voltage vs
Temperature
7.536
7.524
REFERENCE VOLTAGE (V)
300
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)
1248 G03
I
M
(µA)
Supply Current vs Supply Voltage
11
10
9
T
J
= –55°C
18.5
18.0
17.5
17.0
16.5
16.0
15.5
15.0
14.5
14.0
13.5
13.0
10
21
SUPPLY VOLTAGE (V)
32
1248 G05
SUPPLY CURRENT (mA)
GTDR VOLTAGE (V)
7
6
5
4
3
2
1
0
GTDR VOLTAGE (V)
8
T
J
= 125°C
T
J
= 25°C
4
U W
Current Amplifier Open-Loop
Gain and Phase
0
–20
–40
100
80
GAIN
60
40
20
0
–20
–40
–60
–80
–100
–120
10M
1148 G02
0
–20
–100
–120
10M
1148 G01
PHASE (DEG)
PHASE (DEG)
PHASE
1M
10
100
1k
10k 100k
FREQUENCY (Hz)
1M
Multiplier Current
VA
OUT
= 7V
VA
OUT
= 6.5V
VA
OUT
= 6V
150
VA
OUT
= 5V
VA
OUT
= 4.5V
VA
OUT
= 4V
VA
OUT
= 3.5V
0
VA
OUT
= 3V
VA
OUT
= 2.5V
500
1248 G04
VA
OUT
= 5.5V
0
250
I
AC
(µA)
GTDR Source Current
1.1
V
CC
= 18V
GTDR Sink Current
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
T
A
= 25°C
T
A
= 125°C
0
60
120
180
240
SINK CURRENT (mA)
300
1248 G07
T
J
= 125°C
T
J
= 25°C
T
J
= –55°C
T
A
= –55°C
0
–120
–180
–240
– 60
SOURCE CURRENT (mA)
–300
1248 G06
LT1248
TYPICAL PERFOR A CE CHARACTERISTICS
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
1248 G08
GTDR Maximum Duty Cycle vs
R
SET
and C
SET
1.00
0.99
0.98
1.1
1.0
0.9
SUPPLY CURRENT (mA)
MAXIMUM DUTY CYCLE
0.97
0.96
0.95
0.94
0.93
0.92
0.91
0.90
200
600
1000
R
SET
= 10k
R
SET
= 15k
R
SET
= 20k
R
SET
= 30k
1800
1400
C
SET
CAPACITANCE (pF)
2200
1248 G11
Synchronization and Shutdown
Thresholds at EN/SYNC Pin
–44
–40
–36
SHUTDOWN
THRESHOLD
SYNCHRONIZATION
THRESHOLD
T
J
= – 55°C
T
J
= 25°C
T
J
= 125°C
–22
–20
–18
–16
–14
–12
–10
–8
–6
–4
–2
0
1
2
3 4 5
6 7 8
EN/SYNC VOLTAGE (V)
9
10
0
EN/SYNC CURRENT (µA)
–28
–24
–20
–16
–12
–8
–4
0
SS CURRENT (µA)
T
J
= –55°C
T
J
= 25°C
T
J
= 125°C
M
OUT
CURRENT (mA)
–32
U W
1248 G13
Start-Up Supply Current vs
Supply Voltage
500
450
400
350
300
250
200
150
100
50
0
2
4
6 8 10 12 14 16 18 20
SUPPLY VOLTAGE (V)
1248 G09
Frequency vs R
SET
and C
SET
R
SET
= 10k
R
SET
= 15k
R
SET
= 20k
R
SET
= 30k
400
0
200
600
1000
1800
1400
C
SET
CAPACITANCE (pF)
2200
1248 G10
Shutdown Mode Supply Current
and Reference Voltage
1.1
EN/SYNC
≤
1.8V
1.0
0.9
REFERENCE VOLTAGE (V)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
REFERENCE VOLTAGE
T
J
≤
125°C
16
SUPPLY VOLTAGE (V)
SUPPLY CURRENT
–55°C
≤
T
J
≤
25°C
T
J
= 125°C
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
32
1248 G12
SS Pin Characteristics
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
–3.5
0
4
SS VOLTAGE (V)
8
1248 G14
M
OUT
Pin Characteristics
T
J
= 125°C
T
J
= 25°C
T
J
= –55°C
–4.0
–2.4
1.2
–1.2
0
M
OUT
VOLTAGE (V)
2.4
1248 G15
5
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