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LT1937ESC6#TRMPBF

P1-P3P4-P6P7-P9P10-P12
1
LT1937
1937f
White LED
Step-Up Converter in
SC70 and ThinSOT
, LTC and LT are registered trademarks of Linear Technology Corporation.
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.
■
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 0.22µF Output Capacitor
■
Low Profile SC70 and ThinSOT
TM
Packaging
■
Cellular Phones
■
PDAs, Handheld Computers
■
Digital Cameras
■
MP3 Players
■
GPS Receivers
ThinSOT is a trademark of Linear Technology Corporation.
LED CURRENT (mA)
0
60
EFFICIENCY (%)
65
70
75
80
85
90
V
IN
= 3V
5101520
1937 TA01b
V
IN
= 3.6V
Figure 1. Li-Ion Powered Driver for Three White LEDs
Conversion Efficiency
V
IN
SW
LT1937
L1
22µH
C1
1µF
C2
0.22µF
15mA
1937 F01a
V
IN
3V TO 5V
OFF ON
SHDN
R1
6.34Ω
C1, C2: X5R OR X7R DIELECTRIC
D1: CENTRAL SEMICONDUCTOR CMDSH-3
L1: MURATA LQH3C-220 OR EQUIVALENT
FB
LED 3
LED 2
LED 1
D1
GND
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
2
LT1937
1937f
Input Voltage (V
IN
) ................................................. 10V
SW Voltage ............................................................. 36V
FB Voltage .............................................................. 10V
SHDN Voltage ......................................................... 10V
T
JMAX
= 125°C, θ
JA
= 256°C/ W IN FREE AIR
θ
JA
= 120°C ON BOARD OVER GROUND PLANE
ABSOLUTE AXI U RATI GS
WWWU
PACKAGE/ORDER I FOR ATIO
UU
W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
SW 1
GND 2
TOP VIEW
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
FB 3
5 V
IN
4 SHDN
ORDER PART
NUMBER
S5 PART MARKING
LT1937ES5
LTYN
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage 2.5 V
Maximum Operating Voltage 10 V
Feedback Voltage I
SW
= 100mA, Duty Cycle = 66% 86 95 104 mV
FB Pin Bias Current 10 45 100 nA
Supply Current 1.9 2.5 mA
SHDN = 0V 0.1 1.0 µA
Switching Frequency 0.8 1.2 1.6 MHz
Maximum Duty Cycle 85 90 %
Switch Current Limit 320 mA
Switch V
CESAT
I
SW
= 250mA 350 mV
Switch Leakage Current V
SW
= 5V 0.01 5 µA
SHDN Voltage High 1.5 V
SHDN Voltage Low 0.4 V
SHDN Pin Bias Current 65 µA
T
A
= 25°C, V
IN
= 3V, V
SHDN
= 3V, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
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.
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
(Note 1)
ORDER PART
NUMBER
SC6 PART MARKING
LT1937ESC6
LAAB
SW 1
GND 2
FB 3
6 V
IN
5 GND
4 SHDN
TOP VIEW
SC6 PACKAGE
6-LEAD PLASTIC SC70
T
JMAX
= 125°C, θ
JA
= 256°C/ W IN FREE AIR
θ
JA
= 150°C ON BOARD OVER GROUND PLANE
3
LT1937
1937f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Current Limit vs Duty Cycle
Quiescent Current SHDN Pin Bias Current
Switching Frequency
Feedback Bias Current
UU
U
PI FU CTIO S
SW (Pin 1): Switch Pin. Connect inductor/diode here.
Minimize trace area at this pin to reduce EMI.
GND (Pin 2): Ground Pin. Connect directly to local ground
plane.
FB (Pin 3): Feedback Pin. Reference voltage is 95mV.
Connect cathode of lowest LED and resistor here. Calcu-
late resistor value according to the formula:
R
FB
= 95mV/I
LED
SHDN (Pin 4): Shutdown Pin. Connect to 1.5V or higher to
enable device; 0.4V or less to disable device.
GND (Pin 5, SC70 Package): Ground Pin. Connect to Pin
2 and to local ground plane
V
IN
(Pin 5/Pin 6 SC70 Package): Input Supply Pin. Must
be locally bypassed.
V
IN
(V)
0
0
I
Q
(mA)
0.4
0.8
1.2
1.6
2468
1937 G01
10
2.0
0.2
0.6
1.0
1.4
1.8
2.2
–50°C
100°C
25°C
TEMPERATURE (°C)
–50
SHDN PIN BIAS CURRENT (µA)
350
25
1937 G02
200
100
–25 0 50
50
0
400
300
250
150
75 100
SHDN = 10V
SHDN = 3.6V SHDN = 3V
SHDN = 2.7V
TEMPERATURE (°C)
–50
0.8
1.0
1.4
25 75
1937 G03
0.6
0.4
–25 0
50 100
0.2
0
1.2
SWITCHING FREQUENCY (MHz)
TEMPERATURE (°C)
–50
FEEDBACK BIAS CURRENT (nA)
40
50
60
25 75
1937 G04
30
20
–25 0
50 100
10
0
Efficiency vs Temperature
TEMPERATURE (°C)
–50
EFFICIENCY (%)
82
83
1937 G05
81
80
0
50
100
85
84
I
LED
= 20mA
I
LED
= 15mA
I
LED
= 10mA
V
IN
= 3.6V
3 LEDs
DUTY CYCLE (%)
0
350
300
250
200
150
100
50
0
60
1937 G06
20 40 80 100
CURRENT LIMIT (mA)
P1-P3P4-P6P7-P9P10-P12

LT1937ESC6#TRMPBF

Mfr. #:
Buy LT1937ESC6#TRMPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
LED Lighting Drivers White LED Boost Conv in SC70 & SOT
Lifecycle:
New from this manufacturer.
Delivery:
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