LT1372 Linear Technology, LT1372 Datasheet

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LT1372

Manufacturer Part Number
LT1372
Description
500kHz and 1MHz High Efficiency 1.5A Switching Regulators
Manufacturer
Linear Technology
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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LT1372 Summary of contents

Page 1

... 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 ...

Page 2

... A 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

... C 0.9 100 0.8 0.7 0.6 0.5 –55 C 0.4 0.3 0.2 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 SWITCH CURRENT (A) LT1372 • G01 CONDITIONS LT1372/LT1377 LT1372HV 125 C J – < Grade Duty Cycle = 50% Duty Cycle = 80% (Note 1) 2.7V V 25V IN 2.7V V 25V, V 0. 125 C J – < Grade ...

Page 4

... Error Amplifier Output Current vs Feedback Pin Voltage 400 300 25 C –55 C 200 125 C 100 0 –100 –200 –300 125 150 –0.3 –0.2 –0.1 FEEDBACK PIN VOLTAGE (V) LT1372 • G05 Error Amplifier Transconductance vs Temperature 2000 1800 1600 1400 1200 1000 800 600 400 200 0 0.9 1.0 –50 –25 0 ...

Page 5

... S/S (Pin 4): Shutdown and Synchronization Pin. The S/S pin is logic level compatible. Shutdown is active low and the shutdown threshold is typically 1.3V. For normal operation, pull the S/S pin high, tie floating. To synchronize switching, drive the S/S pin be- tween 600kHz and 800kHz (LT1372) or 1.2MHz to 1.6MHz (LT1377). W BLOCK DIAGRAM ...

Page 6

... This low dropout design allows input voltage to vary from 2.7V to 25V with virtually no change in device performance. 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 ...

Page 11

... 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 –15V R4 12. 2.49k 1% LT1372 • TA04 D1 1N4148 D2 1N4148 10k 0.1 F LT1372 • TA06 11 ...

Page 12

... C3 *SINGLE INDUCTOR WITH TWO WINDINGS 100 F COILTRONICS CTX10-1 10V † MAX I OUT I V OUT IN 0.45A 4V 0.55A 5V 0.65A 7V 0.72A 9V LT1372 • TA07 0.400* (10.160) MAX 0.255 0.015 0695 0.189 – 0.197* (4.801 – 5.004 0.150 – 0.157** 0.228 – ...

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