LT1377 Linear Technology Corporation, LT1377 Datasheet

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LT1377

Manufacturer Part Number
LT1377
Description
500kHz and 1MHz High Efficiency 1.5A Switching Regulators
Manufacturer
Linear Technology Corporation
Datasheet

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APPLICATIONS
FEATURES
TYPICAL
+
Boost Regulators
CCFL Backlight Driver
Laptop Computer Supplies
Multiple Output Flyback Supplies
Inverting Supplies
Faster Switching with Increased Efficiency
Uses Small Inductors: 4.7 H
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: 12 A Typ
Easy External Synchronization
8-Pin SO or PDIP Packages
OFF
C1**
22 F
ON
5V-to-12V Boost Converter
4
S/S
GND
LT1372/LT1377
APPLICATION
6, 7
0.047 F
V
5V
IN
U
C2
5
R3
2k
4.7 H
V
V
L1*
SW
C
FB
1
8
2
MBRS120T3
C3
0.0047 F
D1
U
R2
6.19k
1%
R1
53.6k
1%
+
C4**
22 F
V
12V
OUT
**AVX TPSD226M025R0200
*COILCRAFT DO1608-472 (4.7 H) OR
MAX I
4.7 H
COILCRAFT DT3316-103 (10 H) OR
SUMIDA CD43-4R7 (4.7 H) OR
SUMIDA CD73-100KC (10 H) OR
10 H
L1
OUT
0.25A
0.35A
I
OUT
The LT
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 quies-
cent 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 exter-
nal logic level source. A logic low on the shutdown pin
reduces supply current to 12 A. Unique error amplifier
circuitry can regulate positive or negative output voltage
while maintaining simple frequency compensation tech-
niques. Nonlinear error amplifier transconductance re-
duces output overshoot on start-up or overload recovery.
Oscillator frequency shifting protects external compo-
nents during overload conditions.
DESCRIPTION
, LTC and LT are registered trademarks of Linear Technology Corporation.
1.5A Switching Regulators
®
LT1372 • TA01
1372/LT1377 are monolithic high frequency
100
90
60
50
80
70
U
0.01
500kHz and 1MHz
V
IN
= 5V
12V Output Efficiency
High Efficiency
OUTPUT CURRENT (A)
LT1372/LT1377
0.1
LT1372 • TA02
1
1

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LT1377 Summary of contents

Page 1

... All functions of the LT1372/LT1377 are integrated into 8-pin SO/PDIP packages. The LT1372/LT1377 typically consumes only 4mA quies- cent current and has higher efficiency than previous parts. High frequency switching allows for very small inductors to be used ...

Page 2

... BSOLUTE 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 ........................................ 125 C* Industrial ......................................... – 125 C Short Circuit ......................................... 150 C Storage Temperature Range ................ – ...

Page 3

... Note 1: For duty cycles (DC) between 50% and 90%, minimum guaranteed switch current is given by I Switch Current Limit vs Duty Cycle 3.0 2 AND 125 C 2.0 –55 C 1.5 1.0 0 100 DUTY CYCLE (%) LT1372 • G02 LT1372/LT1377 MIN TYP MAX UNITS 130 260 0.5 0.8 1.5 1.9 2.7 A 1.3 1.7 2 ...

Page 4

... THRESHOLD C 1.0 0.8 0.6 0.4 –50 – 100 125 150 TEMPERATURE ( C) LT1372 • G10 4 Minimum Synchronization Voltage vs Temperature 2.0 3 700kHz (LT1372) SYNC 1 1.4MHz (LT1377) SYNC 2.5 1.6 1.4 2.0 1.2 LT1377 1.0 1.5 0.8 LT1372 1.0 0.6 0.4 0.5 0 –50 – ...

Page 5

... Keep the traces to the switching components as short as possible to minimize radiation and voltage spikes. or leave LOW DROPOUT 2.3V REG LOGIC OSC 5:1 FREQUENCY SHIFT COMP LT1372/LT1377 drops below IN compensation network C SW ANTI-SAT DRIVER SWITCH + 0.08 – GND LT1372 • ...

Page 6

... A 500kHz (LT1372) or 1MHz (LT1377) oscillator is the basic clock for all internal timing. It turns “On” the output switch via the logic and driver circuitry. Special adaptive anti-sat ...

Page 7

... resetable shutdown delay network guarantees the part will not go into shutdown while receiving a synchro- nization signal. Caution should be used when synchronizing above 700kHz (LT1372) or 1.4MHz (LT1377) because at higher sync frequencies the amplitude of the internal slope compensa ...

Page 8

... At 500kHz, any polarized capacitor is essentially resistive. To get low ESR takes volume , so physically smaller capacitors have high ESR. The ESR range for typical LT1372 and LT1377 applications is 0. typical output capacitor is an AVX type TPS 25V, with a guaranteed ESR less than 0.2 . ...

Page 9

... RIPPLE RIPPLE CURRENT (A) 0 500kHz Switching frequency (LT1372) or, 0.4 1MHz Switching frequency (LT1377) 0.7 to 1.1 The input capacitor can see a very high surge current when 0.36 to 0.24 a battery or high capacitance source is connected “live” and solid tantalum capacitors can fail under this condition. ...

Page 10

... Application Note 19. Linear Technol- C ogy also offers a computer software program, SwitcherCAD, to assist in designing switching converters. SwitcherCAD pin reduces will be updated in late 1995 for the LT1372 and LT1377 addition, our applications department is always ready to lend a helping hand. SWITCH L1 ...

Page 11

... MAX LAMP C2 10 27pF 0 330 1N5818 2 562 * 20k LT1372/LT1377 DIMMING GND V C 22k 1N4148 2 F OPTIONAL REMOTE DIMMING CCFL BACKLIGHT APPLICATION CIRCUITS CONTAINED IN THIS DATA SHEET ARE COVERED BY U.S. PATENT NUMBER 5408162 AND OTHER PATENTS PENDING V OUT 15V + –V OUT – ...

Page 12

... Linear Technology Corporation 12 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 : (408) 434-0507 FAX TELEX N 2 Li-Ion Cell to 5V SEPIC Converter L1A MBRS130LT3 V IN • S LT1372/LT1377 18. • GND V C L1B 6.19k 0.0047 F 0.047 F U Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0 ...

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