Linear Technology LT1248 Datasheet

FEATURES

LT1248

Power Factor Controller

U

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

U

APPLICATIO S

■

Universal Power Factor Corrected Power Supplies

■

Preregulators Up To 1500W

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.

BLOCK DIAGRA

+

V

CC

2.6V/

2.2V

7.5V

7.9V

12µA

–

–

+

–

EA

+

+

–

5V

16V TO 10V

EN/SYNC

10

V

SENSE

11

I

AC

6

OVP

8

SS
13

W

–

CA

+

CA

PK

OUT

32

–

+

+

0.7V

–

SYNC

C

SET

LIM

GND

1

–

+

R
R

Q

S

RUN

OSC

1 6V

1214

R

SET

V

CC

15

16

GTDR

1248 BD

M

OUTISENSE

4

5

7µA

I

2

M

I

A

B

2

32k

+

M1

–

I

A

I

B

ONE SHOT

V

REF

9

7.5V

V

REF

IM =

200ns

RUN

I

200µA

VA

OUT

7

2.2V

–

+

1

LT1248

A

W

O

LUTEXI TIS

S

A

WUW

ARB

U
G

PACKAGE

/

O

RDER I FOR ATIO

WU

U

(Note 1)

Supply Voltage ....................................................... 27V

GTDR Current Continuous ..................................... 0.5A

GTDR Output Energy(Per Cycle) .............................. 5µJ

IAC, R
V

SENSE

I

SENSE

SET

, PK

Input Current............................. 20mA

LIM

, EN/SYNC, OVP Input Voltage................... V

, M

Input Current.................................. ±5mA

OUT

MAX

Operating Junction Temperature Range

LT1248C................................................ 0°C to 100°C

LT1248I ........................................... –40°C to 125°C

GND

PK
CA
I

SENSE

M

VA

OVP

LIM

OUT

OUT

I

OUT

AC

Thermal Resistance (Junction-to-Ambient)

N Package .................................................. 100°C/W

S Package................................................... 120°C/W

Storage Temperature Range ..................–65°C to 150°C

16-LEAD NARROW PLASTIC SO

T
T

Lead Temperature (Soldering, 10 sec)................. 300°C

Consult factory for Military grade parts.

LECTRICAL C CHARA TERIST

E

ture range, otherwise specifications are at T
C

= 1nF to GND, I

SET

PARAMETER CONDITIONS MIN TYP MAX UNITS
Overall

Supply Current (VCC in Undervoltage Lockout) VCC = Lockout Voltage – 0.2V ● 0.25 0.45 mA
Supply Current (Inactive) EN/SYNC = 0V, VCC ≤ V
Supply Current, On 11.5V ≤ VCC ≤ V
VCC Turn-On Threshold (Undervoltage Lockout) ● 15.5 16.5 17.5 V
VCC Turn-Off Threshold ● 9.5 10.5 11.5 V
EN/SYNC Threshold, Rising ● 2.2 2.6 2.85 V
EN/SYNC Threshold Hysteresis 0.40 V
EN/SYNC Input Current EN/SYNC = 0V ● –5 –1 5 µA

Voltage Amplifier

Voltage Amp Offset Voltage VA
Input Bias Current V
Voltage Gain 70 100 dB
Voltage Amp Unity-Gain Bandwidth 3 MHz
Voltage Amp Output High (Internally Clamped) ● 11.3 13.3 V
Voltage Amp Output Low ● 1.1 2 V
Voltage Amp Short-Circuit Current VA
SS Current SS = 2.5V ● 51230 µA

Current Amplifier

Current Amp Offset Voltage ● ±1 ±4mV
I

Bias Current ● – 25 –250 nA

SENSE

Current Amp Voltage Gain 80 110 dB
Current Amp Unity-Gain Bandwidth 3 MHz
Current Amp Output High ● 7.2 8.5 V
Current Amp Output Low ● 1.1 2 V

= 100µA, I

AC

SENSE

= 0V, CA

ICS

= 25°C. Maximum operating voltage (V

A

OUT

The ● denotes specifications which apply over the full operating tempera-

= 3.5V, VA

3V ≤ EN/SYNC ≤ 7V –50 – 25 50 µA

OUT

SENSE

OUT

= 5V, OVP = 7.5V, no load on any outputs, unless otherwise noted.

OUT

MAX

, CA

MAX

OUT

= 3.5V ● –8 8 mV

= 0V to 7V ● – 25 –250 nA

= 0V ● 51430 mA

TOP VIEW

1
2
3
4
5
6
7
8

N PACKAGE

16-LEAD PDIP

S PACKAGE

= 125°C, θJA = 100°C/W (N)

JMAX

= 125°C, θJA = 120°C/W (S)

JMAX

) = 25V, VCC = 18V, R

MAX

= 1V ● 8.5 12.0 mA

GTDR

16

V

15

CC

C

14

SET

SS

13

R

12

SET

V

11

SENSE

EN/SYNC

10

V

9

REF

● 0.5 1.5 mA

ORDER PART

NUMBER

LT1248CN
LT1248IN
LT1248CS
LT1248IS

= 15k to GND,

SET

2

LT1248

LECTRICAL C CHARA TERIST

E

ture range, otherwise specifications are at T
C

= 1nF to GND, I

SET

= 100µA, I

AC

SENSE

A

= 0V, CA

ICS

= 25°C. Maximum operating voltage (V

OUT

The ● denotes specifications which apply over the full operating tempera-

= 3.5V, VA

) = 25V, VCC = 18V, R

= 5V, OVP = 7.5V, no load on any outputs, unless otherwise noted.

OUT

MAX

= 15k to GND,

SET

PARAMETER CONDITIONS MIN TYP MAX UNITS
Current Amplifier

Current Amp Short-Circuit Current CA
Input Range, I

SENSE

, M

(Linear Operation) ● –0.3 1 V

OUT

= 0V ● 51430 mA

OUT

Reference

Reference Output Voltage I
V

Load Regulation –5mA < I

REF

V

Line Regulation 11.5V < VCC < V

REF

V

Short-Circuit Current V

REF

V

Worst Case Load, Line, Temperature ● 7.32 7.5 7.68 V

REF

= 0mA, TA = 25°C 7.39 7.50 7.60 V

REF

< 0mA 5 mV

REF

MAX

= 0V ● 12 28 50 mA

REF

● –20 5 20 mV

Current Limit

PK

Offset Voltage ● –15 15 mV

LIM

PK

Input Current PK

LIM

PK

to GTDR Propagation Delay PK

LIM

= –0.1V ● – 50 –100 µA

LIM

Falling from 50mV to –50mV 400 ns

LIM

Multiplier

Multiplier Output Current IAC = 100µA, R

= 15k 35 µA

SET

Multiplier Output Current Offset RAC = 1M from IAC to GND ● –0.05 –0.5 µA
Multiplier Maximum Output Current IAC = 450µA, R

= 15k, VA

SET

OUT

= 7V, M

= 0V ● –286 –260 – 235 µA

OUT

Multiplier Gain Constant (Note 2) 0.035 V
IAC Input Resistance IAC from 50µA to 1mA 15 32 50 kΩ

Oscillator

Oscillator Frequency R

C

Ramp Peak-to-Peak Amplitude 4.35 4.7 5.0 V

SET

C

Ramp Valley Voltage 1.25 1.4 1.55 V

SET

Synchronization Pulse Threshold on EN/SYNC Pin
Synchronization Frequency Range

SET

R

SET

= 15k, C
= 15k, C

= 1000pF ● 85 100 115 kHz

SET

= 1500pF ● 58 68 78 kHz

SET

Pulse Low = 3.5V, High = 7V, Width > 200ns
R

SET

= 15k, C

= 1000pF

SET

4.5 5.6 6.5 V

● 1.2 1.6 f

NOM

Overvoltage Comparator

Comparator Trip Voltage Ratio (V

TRIP/VREF

) ● 1.04 1.05 1.06

Hysteresis 0.35 V
OVP Bias Current OVP = 7.5V ● –50 – 250 nA
OVP Propagation Delay 100 ns

Gate Driver

Max GTDR Output Voltage 0mA Load, 18V < V

CC

GTDR Output High –200mA Load, 11.5V ≤ VCC ≤ 15V ● V

● 12 15 17.5 V

– 3.0 V

CC

GTDR Output Low (Device Unpowered) VCC = 0V, 50mA Load (Sinking) ● 0.9 1.5 V
GTDR Output Low (Device Active) 200mA Load (Sinking) ● 0.5 1 V

10mA Load

● 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 %

–2

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired

I

Note 2: Multiplier Gain Constant: K =

IAC (VA

M

OUT

– 2)

2

3

LT1248

LPER

UW

R

F

O

ATYPICA

CCHARA TERIST

E

C

ICS

Voltage Amplifier Open-Loop
Gain and Phase

100

80

60

40

GAIN (dB)

20

0

–20

10

100

GAIN

PHASE

1k 10k 100k

FREQUENCY (Hz)

Reference Voltage vs
Temperature

7.536

7.524

7.512

7.500

7.488

7.476

7.464

REFERENCE VOLTAGE (V)

7.452

7.440

7.428
–50 150

–75

0 25 50 100

–25

JUNCTION TEMPERATURE (°C)

75

1M 10M

1148 G01

125

1248 G03

0

–20

–40

–60

–80

–100

–120

PHASE (DEG)

Current Amplifier Open-Loop
Gain and Phase

100

80

GAIN

60

40

GAIN (dB)

–20

20

0

10

100

PHASE

1k 10k 100k

FREQUENCY (Hz)

Multiplier Current

300

VA

= 7V

OUT

VA

= 6.5V

OUT

VA

= 6V

OUT

150

(µA)

M

I

0

0

250

IAC (µA)

1M 10M

1148 G02

500

1248 G04

0

–20

–40

–60

–80

–100

–120

VA

VA

VA

VA

VA
VA

VA

OUT

OUT

OUT

OUT

OUT
OUT

OUT

PHASE (DEG)

= 5.5V

= 5V

= 4.5V

= 4V

= 3.5V
= 3V

= 2.5V

Supply Current vs Supply Voltage GTDR Source Current

11
10

TJ = –55°C

9
8
7
6
5
4
3

SUPPLY CURRENT (mA)

2
1
0

10

SUPPLY VOLTAGE (V)

TJ = 25°CTJ = 125°C

21

32

1248 G05

18.5
VCC = 18V

18.0

17.5

17.0

16.5

16.0

15.5

15.0

GTDR VOLTAGE (V)

14.5

14.0

13.5

13.0

0

–60

SOURCE CURRENT (mA)

4

TJ = 125°C

TJ = 25°C

TJ = –55°C

–120 –180 –240

1248 G06

–300

GTDR Sink Current

1.1

1.0

0.9

0.8

0.7

0.6

0.5
TA = –55°C

0.4

GTDR VOLTAGE (V)

0.3

0.2

0.1

0

TA = 125°C

0

TA = 25°C

60

120 180 240

SINK CURRENT (mA)

300

1248 G07