ANALOG DEVICES LT 1372 CS8 Datasheet

FEATURES

LT1372/LT1377

500kHz and 1MHz

High Efficiency

1.5A Switching Regulators

U

DESCRIPTIO

■

Faster Switching with Increased Efficiency

■

Uses Small Inductors: 4.7µH

■

All Surface Mount Components

■

Only 0.5 Square Inch of Board Space

■

Low Minimum Supply Voltage: 2.7V

■

Quiescent Current: 4mA Typ

■

Current Limited Power Switch: 1.5A

■

Regulates Positive or Negative Outputs

■

Shutdown Supply Current: 12µA Typ

■

Easy External Synchronization

■

8-Pin SO or PDIP Packages

U

APPLICATIO S

■

Boost Regulators

■

CCFL Backlight Driver

■

Laptop Computer Supplies

■

Multiple Output Flyback Supplies

■

Inverting Supplies

The LT®1372/LT1377 are monolithic high frequency
switching regulators. They can be operated in all standard
switching configurations including boost, buck, flyback,
forward, inverting and “Cuk.” A 1.5A high efficiency switch
is included on the die, along with all oscillator, control and
protection circuitry. All functions of the LT1372/LT1377
are integrated into 8-pin SO/PDIP packages.

The LT1372/LT1377 typically consumes only 4mA quies­cent current and has higher efficiency than previous parts.
High frequency switching allows for very small inductors
to be used. All surface mount components consume less
than 0.5 square inch of board space.

New design techniques increase flexibility and maintain
ease of use. Switching is easily synchronized to an exter­nal logic level source. A logic low on the shutdown pin
reduces supply current to 12µA. Unique error amplifier
circuitry can regulate positive or negative output voltage
while maintaining simple frequency compensation tech­niques. Nonlinear error amplifier transconductance re­duces output overshoot on start-up or overload recovery.
Oscillator frequency shifting protects external compo­nents during overload conditions.

, LTC and LT are registered trademarks of Linear Technology Corporation.

TYPICAL APPLICATIO

5V-to-12V Boost Converter

5V

L1*

4.7µH

5

V

4

ON

OFF

+ +

C1**
22µF

IN

S/S

LT1372/LT1377

GND

6, 7

C2

0.047µF

V

SW

FB

V

C

1

R3

2k

MBRS120T3

8

2

C3

0.0047µF

D1

U

R1

53.6k
1%

R2

6.19k
1%

†

V

OUT

12V

*FOR LT1372 USE 10µH
COILCRAFT DO1608-472 (4.7µH) OR
COILCRAFT DT3316-103 (10µH) OR

C4**

SUMIDA CD43-4R7 (4.7µH) OR

22µF

SUMIDA CD73-100KC (10µH) OR
**AVX TPSD226M025R0200

†MAX I

OUT

I

OUT

(LT1377)

0.25A

0.35A

L1

4.7µH
10µH

I

OUT

(LT1372)

NA

0.29A

LT1372 • TA01

100

VIN = 5V

90

80

70

EFFICIENCY (%)

60

50

0.01

12V Output Efficiency

0.1 1

OUTPUT CURRENT (A)

LT1372 • TA02

1

LT1372/LT1377

PACKAGE/ORDER I FOR ATIO

UU

W

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

Supply Voltage ....................................................... 30V

Switch Voltage

LT1372/LT1377 .................................................. 35V

LT1372HV .......................................................... 42V

S/S Pin Voltage....................................................... 30V

Feedback Pin Voltage (Transient, 10ms) .............. ±10V

Feedback Pin Current........................................... 10mA

Negative Feedback Pin Voltage

(Transient, 10ms)............................................. ±10V

Operating Junction Temperature Range

Commercial ........................................ 0°C to 125°C*

Industrial ......................................... – 40°C to 125°C

Short Circuit ......................................... 0°C to 150°C

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

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

ORDER PART NUMBER

TOP VIEW

V

1

C

FB

2

NFB

3

S/S

4

N8 PACKAGE
8-LEAD PDIP

T

= 125°C, θ

JMAX

T

JMAX

Consult factory for parts specified with wider operating temperature ranges.
*Units shipped prior to Date Code 9552 are rated at 100°C maximum
operating temperature.

= 125°C, θ

JA
JA

V

8

GND

7

GND S

6

V

5

S8 PACKAGE

8-LEAD PLASTIC SO

= 100°C/ W (N8)
= 120°C/ W (S8)

LT1372CN8

SW

LT1372HVCN8
LT1372CS8
LT1372HVCS8

IN

LT1372IN8

LT1372HVIN8
LT1372IS8
LT1372HVIS8
LT1377CS8
LT1377IS8

S8 PART MARKING

1372
1372I

1372H
1372HI

1377
1377I

ELECTRICAL CHARACTERISTICS

The ● denotes specifcatons which appy over the full operating temperature range, otherwise specifications are at TA = 25°C.
VIN = 5V, VC = 0.6V, VFB = V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

REF

I

FB

V

NFB

I

NFB

g

m

A

V

f Switching Frequency 2.7V ≤ VIN ≤ 25V

Reference Voltage Measured at Feedback Pin 1.230 1.245 1.260 V

Feedback Input Current VFB = V

Reference Voltage Line Regulation 2.7V ≤ VIN ≤ 25V, VC = 0.8V ● 0.01 0.03 %/V
Negative Feedback Reference Voltage Measured at Negative Feedback Pin –2.540 – 2.490 –2.440 V

Negative Feedback Input Current V
Negative Feedback Reference Voltage 2.7V ≤ VIN ≤ 25V, VC = 0.8V ● 0.01 0.05 %/V

Line Regulation
Error Amplifier Transconductance ∆IC = ±25µA 1100 1500 1900 µmho

Error Amplifier Source Current VFB = V
Error Amplifier Sink Current VFB = V
Error Amplifier Clamp Voltage High Clamp, VFB = 1V 1.70 1.95 2.30 V

Error Amplifier Voltage Gain 500 V/V
VC Pin Threshold Duty Cycle = 0% 0.8 1 1.25 V

, VSW, S/S and NFB pins open, unless otherwise noted.

REF

V

= 0.8V ● 1.225 1.245 1.265 V

C

REF

Feedback Pin Open, V

= V

NFB

NFR

– 150mV, VC = 1.5V ● 120 200 350 µA

REF

+ 150mV, VC = 1.5V ● 1400 2400 µA

REF

Low Clamp, V

LT1372 450 500 550 kHz
0°C ≤ TJ ≤ 125°C ● 430 500 580 kHz
–40°C ≤ T
LT1377 0.90 1 1.10 MHz
0°C ≤ TJ ≤ 125°C ● 0.86 1 1.16 MHz
–40°C ≤ T

FB

< 0°C (I Grade) 400 580 kHz

J

< 0°C (I Grade) 0.80 1.16 MHz

J

= 0.8V ● –2.570 – 2.490 –2.410 V

C

= 1.5V 0.25 0.40 0.52 V

250 550 nA

● 900 nA

● –45 –30 –15 µA

● 700 2300 µmho

2

LT1372/LT1377

TEMPERATURE (°C)

–50

1.8

INPUT VOLTAGE (V)

2.0

2.2

2.4

2.6

050

100

150

LT1372 • G03

2.8

3.0

–25 25

75

125

ELECTRICAL CHARACTERISTICS

The ● denotes specifcatons which appy over the full operating temperature range, otherwise specifications are at TA = 25°C.
VIN = 5V, VC = 0.6V, VFB = V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Maximum Switch Duty Cycle ● 85 95 %
Switch Current Limit Blanking Time 130 260 ns

BV Output Switch Breakdown Voltage LT1372/LT1377 ● 35 47 V

V
I

∆I
∆I

I

SAT

LIM

IN
SW

Q

Output Switch “On” Resistance ISW = 1A ● 0.5 0.8 Ω
Switch Current Limit Duty Cycle = 50% ● 1.5 1.9 2.7 A

Supply Current Increase During Switch On-Time 15 25 mA/A

Control Voltage to Switch Current 2A/V
Transconductance

Minimum Input Voltage ● 2.4 2.7 V
Supply Current 2.7V ≤ VIN ≤ 25V ● 4 5.5 mA
Shutdown Supply Current 2.7V ≤ VIN ≤ 25V, V

Shutdown Threshold 2.7V ≤ VIN ≤ 25V ● 0.6 1.3 2 V
Shutdown Delay ● 51225µs
S/S Pin Input Current 0V ≤ V
Synchronization Frequency Range LT1372 ● 600 800 kHz

, VSW, S/S and NFB pins open, unless otherwise noted.

REF

LT1372HV
0°C ≤ TJ ≤ 125°C ● 42 47 V
–40°C ≤ T

< 0°C (I Grade) 40 V

J

Duty Cycle = 80% (Note 2)

≤ 0.6V

0°C ≤ T

J

–40°C ≤ T

≤ 5V ● –10 15 µA

S/S

≤ 125°C ● 12 30 µA

S/S

< 0°C (I Grade) 50 µA

J

LT1377

● 1.3 1.7 2.5 A

● 1.2 1.6 MHz

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

TYPICAL PERFORMANCE CHARACTERISTICS

SWITCH SATURATION VOLTAGE (V)

Switch Saturation Voltage
vs Switch Current

1.0

0.9

0.8

0.7

0.2

0.1

0.6

0.5

0.4

0.3

0

0.2

0.4

0

0.6

SWITCH CURRENT (A)

0.8

100°C

1.0

1.2

150°C

–55°C

1.4

1.6

W

25°C

1.8

LT1372 • G01

2.0

U

3.0

2.5

2.0

1.5

1.0

SWITCH CURRENT LIMIT (A)

0.5

0

Note 2: For duty cycles (DC) between 50% and 90%, minimum
guaranteed switch current is given by I

Switch Current Limit
vs Duty Cycle

20 40 60 80

DUTY CYCLE (%)

–55°C

25°C AND
125°C

LT1372 • G02

= 0.667 (2.75 – DC).

LIM

Minimum Input Voltage
vs Temperature

10010030 50 70 90

3

LT1372/LT1377

FEEDBACK PIN VOLTAGE (V)

400

ERROR AMPLIFIER OUTPUT CURRENT (µA)

–300

–200

–100

300

100

–0.1 0.1

200

0

–0.3 –0.2

V

REF

–55°C

125°C

25°C

LT1372 • G06

TEMPERATURE (°C)

–50

0

TRANSCONDUCTANCE (µmho)

200

600

800

1000

2000

1400

0

50

75

LT1372 • G09

400

1600

1800

1200

–25 25

100

125

150

gm =

∆I (V

C

)

∆V (FB)

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Shutdown Delay and Threshold
vs Temperature

20
18
16
14
12
10

8
6

SHUTDOWN DELAY (µs)

4
2
0

–50

SHUTDOWN THRESHOLD

SHUTDOWN DELAY

–25 25

0

TEMPERATURE (°C)

50

75

S/S Pin Input Current
vs Voltage

5

VIN = 5V

4
3
2
1

0
–1
–2
–3

S/S PIN INPUT CURRENT (µA)

–4
–5

1

2

08

–1

S/S PIN VOLTAGE (V)

5

3

4

100

6

125

LT1372 • G04

7

LT1372 • G07

)

3.0

P-P

SHUTDOWN THRESHOLD (V)

2.5

2.0

1.5

1.0

0.5

MINIMUM SYNCHRONIZATION VOLTAGE (V

110
100

90
80
70
60
50
40
30
20

SWITCHING FREQUENCY (% OF TYPICAL)

10

150

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2
0

9

Minimum Synchronization
Voltage vs Temperature

f

= 700kHz (LT1372)

SYNC

= 1.4MHz (LT1377)

f

SYNC

LT1377

LT1372

0

–50

050

–25 25

TEMPERATURE (°C)

75

Switching Frequency
vs Feedback Pin Voltage

0.2

0

0.3

0.1 0.9
FEEDBACK PIN VOLTAGE (V)

0.4

0.5

0.6

0.7

100

0.8

125

LT1372 • G05

LT1372 • G08

Error Amplifier Output Current
vs Feedback Pin Voltage

150

Error Amplifier Transconductance
vs Temperature

1.0

VC Pin Threshold and High
Clamp Voltage vs Temperature

2.4

2.2

2.0

1.8

1.6

1.4

1.2

PIN VOLTAGE (V)

C

1.0

V

0.8

0.6

0.4

4

–50

–25 25

VC HIGH CLAMP

VC THRESHOLD

0

TEMPERATURE (°C)

50

75

100

125

LT1372 • G10

150

Feedback Input Current
vs Temperature

800

VFB =V

0

–50

–25

REF

0

50

25

TEMPERATURE (°C)

700

600

500

400

300

200

FEEDBACK INPUT CURRENT (nA)

100

Negative Feedback Input Current
vs Temperature

0

V

=V

NFB

NFR

–10

–20

–30

–40

NEGATIVE FEEDBACK INPUT CURRENT (µA)

–50

–50

–25 25

75

100

125

LT1372 • G11

150

0

50

TEMPERATURE (°C)

75

100

125

LT1372 • G12

150