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Linear Technology Electronic Components Datasheet

LT1937 Datasheet

White LED Step-Up Converter in SC70 and ThinSOT

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FEATURES
s Inherently Matched LED Current
s High Efficiency: 84% Typical
s Drives Up to Four LEDs from a 3.2V Supply
s Drives Up to Six LEDs from a 5V Supply
s 36V Rugged Bipolar Switch
s Fast 1.2MHz Switching Frequency
s Uses Tiny 1mm Tall Inductors
s Requires Only 0.22µF Output Capacitor
s Low Profile SC70 and ThinSOTTM Packaging
U
APPLICATIO S
s Cellular Phones
s PDAs, Handheld Computers
s Digital Cameras
s MP3 Players
s GPS Receivers
LT1937
White LED
Step-Up Converter in
SC70 and ThinSOT
DESCRIPTIO
The LT®1937 is a step-up DC/DC converter specifically
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
0.22µF, 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
VIN
3V TO 5V
OFF ON
L1
22µH
D1
C1 C2
1µF
LED 1
0.22µF
VIN SW LED 2
15mA
LT1937
LED 3
SHDN
FB
GND R1
6.34
C1, C2: X5R OR X7R DIELECTRIC
D1: CENTRAL SEMICONDUCTOR CMDSH-3
L1: MURATA LQH3C-220 OR EQUIVALENT
1937 F01a
Figure 1. Li-Ion Powered Driver for Three White LEDs
Conversion Efficiency
90
85
80
VIN = 3V VIN = 3.6V
75
70
65
60
0
5 10 15
LED CURRENT (mA)
20
1937 TA01b
1937f
1


Linear Technology Electronic Components Datasheet

LT1937 Datasheet

White LED Step-Up Converter in SC70 and ThinSOT

No Preview Available !

LT1937
ABSOLUTE AXI U RATI GS (Note 1)
Input Voltage (VIN) ................................................. 10V
SW Voltage ............................................................. 36V
FB Voltage .............................................................. 10V
SHDN Voltage ......................................................... 10V
Extended Commercial
Operating Temperature Range (Note 2)... – 40°C to 85°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
UW U
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SW 1
GND 2
FB 3
5 VIN
4 SHDN
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
TJMAX = 125°C, θJA = 256°C/ W IN FREE AIR
θJA = 120°C ON BOARD OVER GROUND PLANE
ORDER PART
NUMBER
LT1937ES5
S5 PART MARKING
LTYN
TOP VIEW
SW 1
GND 2
FB 3
6 VIN
5 GND
4 SHDN
SC6 PACKAGE
6-LEAD PLASTIC SC70
TJMAX = 125°C, θJA = 256°C/ W IN FREE AIR
θJA = 150°C ON BOARD OVER GROUND PLANE
ORDER PART
NUMBER
LT1937ESC6
SC6 PART MARKING
LAAB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS TA = 25°C, VIN = 3V, VSHDN = 3V, unless otherwise noted.
PARAMETER
Minimum Operating Voltage
Maximum Operating Voltage
Feedback Voltage
FB Pin Bias Current
Supply Current
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch VCESAT
Switch Leakage Current
SHDN Voltage High
SHDN Voltage Low
SHDN Pin Bias Current
CONDITIONS
ISW = 100mA, Duty Cycle = 66%
SHDN = 0V
ISW = 250mA
VSW = 5V
MIN TYP MAX
2.5
10
86 95 104
10 45 100
1.9 2.5
0.1 1.0
0.8 1.2 1.6
85 90
320
350
0.01 5
1.5
0.4
65
UNITS
V
V
mV
nA
mA
µA
MHz
%
mA
mV
µA
V
V
µA
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: The LT1937E is guaranteed to meet specifications from 0°C to
70°C. Specifications over the –40°C to 85°C operating temperature range
are assured by design, characterization and correlation with statistical
process controls.
1937f
2


Part Number LT1937
Description White LED Step-Up Converter in SC70 and ThinSOT
Maker Linear Technology
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LT1937 Datasheet PDF






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