LT1937ESC6 Linear Technology, LT1937ESC6 Datasheet

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LT1937ESC6

Manufacturer Part Number
LT1937ESC6
Description
White LED Step-Up Converter in SC70 and ThinSOT
Manufacturer
Linear Technology
Datasheet

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FEATURES
TYPICAL APPLICATIO
APPLICATIO S
3V TO 5V
Inherently Matched LED Current
High Efficiency: 84% Typical
Drives Up to Four LEDs from a 3.2V Supply
Drives Up to Six LEDs from a 5V Supply
36V Rugged Bipolar Switch
Fast 1.2MHz Switching Frequency
Uses Tiny 1mm Tall Inductors
Requires Only 0.22 F Output Capacitor
Low Profile SC70 and ThinSOT
Cellular Phones
PDAs, Handheld Computers
Digital Cameras
MP3 Players
GPS Receivers
OFF ON
Figure 1. Li-Ion Powered Driver for Three White LEDs
V
IN
C1, C2: X5R OR X7R DIELECTRIC
D1: CENTRAL SEMICONDUCTOR CMDSH-3
L1: MURATA LQH3C-220 OR EQUIVALENT
C1
1 F
U
SHDN
V
IN
LT1937
22 H
GND
L1
SW
FB
LED 1
LED 2
LED 3
D1
U
TM
Packaging
R1
6.34
15mA
1937 F01a
C2
0.22 F
DESCRIPTIO
The LT
designed to drive white LEDs with a constant current. The
device can drive two, three or four LEDs in series from a
Li-Ion cell. Series connection of the LEDs provides iden-
tical LED currents resulting in uniform brightness and
eliminating the need for ballast resistors. The LT1937
switches at 1.2MHz, allowing the use of tiny external
components. The output capacitor can be as small as
0.22 F, saving space and cost versus alternative solu-
tions. A low 95mV feedback voltage minimizes power loss
in the current setting resistor for better efficiency.
The LT1937 is available in low profile SC70 and ThinSOT
packages.
ThinSOT is a trademark of Linear Technology Corporation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
®
1937 is a step-up DC/DC converter specifically
90
85
80
75
70
65
60
Step-Up Converter in
0
V
IN
= 3V
SC70 and ThinSOT
Conversion Efficiency
U
5
LED CURRENT (mA)
V
IN
= 3.6V
10
15
White LED
1937 TA01b
20
LT1937
1
1937f

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LT1937ESC6 Summary of contents

Page 1

... Packaging tions. A low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. The LT1937 is available in low profile SC70 and ThinSOT packages. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. C2 0.22 F 15mA R1 6 ...

Page 2

... Note 2: The LT1937E is guaranteed to meet specifications from Specifications over the – operating temperature range are assured by design, characterization and correlation with statistical process controls. ORDER PART NUMBER TOP VIEW LT1937ESC6 GND 4 SHDN SC6 PART MARKING SC6 PACKAGE ...

Page 3

W U TYPICAL PERFOR A CE CHARACTERISTICS Quiescent Current 2.2 –50 C 2.0 1.8 100 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0 (V) IN 1937 G01 Feedback Bias ...

Page 4

LT1937 W BLOCK DIAGRA (PIN 6 FOR 5 3 SC70 PACKAGE) 95mV V REF 1.25V SHDN 4 SHUTDOWN U OPERATIO The LT1937 uses a constant frequency, current mode control scheme to provide excellent line and load regula- ...

Page 5

U U APPLICATIO S I FOR ATIO Inductor Selection inductor is recommended for most LT1937 appli- cations. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2MHz and low ...

Page 6

LT1937 U U APPLICATIO S I FOR ATIO LED Current Control The LED current is controlled by the feedback resistor (R1 in Figure 1). The feedback reference is 95mV. The LED current is 95mV/R1. In order to have accurate LED ...

Page 7

U U APPLICATIO S I FOR ATIO 2. Using a DC Voltage For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The dimming control using a DC voltage is shown ...

Page 8

LT1937 U U APPLICATIO S I FOR ATIO D1 2.2nF R2 D2 LT1937 D2: MMBT (11a) Recommended Soft-Startup Circuit Figure 11. Recommended Soft-Startup Circuit and Waveforms Board Layout Consideration As with all switching regulators, careful attention must ...

Page 9

U TYPICAL APPLICATIO S Li-Ion to Two White LEDs DIMMING LT1937 SHDN FB GND C : TAIYO YUDEN JMK107BJ105 ...

Page 10

LT1937 U U TYPICAL APPLICATIO S TYPICAL APPLICATIO S Li-Ion to Five White LEDs DIMMING 90k LT1937 SHDN FB GND C : ...

Page 11

... DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. ...

Page 12

... No Inductor Required, Digital Brightness Adjust, MS8 Package www.linear.com C OUT 0. 1937 TA02a Switching Waveforms 1937 TA02c = 3.6V 0.2 s/DIV V IN FOUR LEDs 15mA , 15V 10V, Drives Up to Eight LEDs from 3V Input, IN LT/TP 0702 2K • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2002 , OUT Q 1937f ...

Page 13

... This datasheet has been download from: www.datasheetcatalog.com Datasheets for electronics components. ...

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