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PDF LT1937ESC6 Data sheet ( Hoja de datos )
| Número de pieza | LT1937ESC6 | |
| Descripción | White LED Step-Up Converter in SC70 and ThinSOT | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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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
6.34Ω
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
1 page  
LT1937
APPLICATIO S I FOR ATIO
Inductor Selection
A 22µH 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 DCR (copper wire resistance). Some
inductors in this category with small size are listed in
Table␣ 1. The efficiency comparison of different inductors
is shown in Figure 4.
Table 1. Recommended Inductors
PART NUMBER
CURRENT
DCR RATING
(Ω) (mA)
LQH3C220
0.71 250
ELJPC220KF
4.0 160
CDRH3D16-220 0.53
350
LB2012B220M
1.7
75
LEM2520-220
5.5
125
MANUFACTURER
Murata
814-237-1431
www.murata.com
Panasonic
714-373-7334
www.panasonic.com
Sumida
847-956-0666
www.Sumida.com
Taiyo Yuden
408-573-4150
www.t-yuden.com
Taiyo Yuden
408-573-4150
www.t-yuden.com
90
VIN = 3.6V
85 3LEDs
80
75
70
65
MURATA LQH3C-220
60 PANASONIC ELJPC220KF
SUMIDA CDRH3D16-220
55 TAIYO YUDEN LB2012B220M
TAIYO YUDEN LEM2520-220
50
0 2 4 6 8 10 12 14 16 18 20
LOAD CURRENT (mA)
1937 F04
Figure 4. Efficiency Comparison of Different Inductors
Capacitor Selection
The small size of ceramic capacitors makes them ideal for
LT1937 applications. X5R and X7R types are recom-
mended because they retain their capacitance over wider
voltage and temperature ranges than other types such as
Y5V or Z5U. A 1µF input capacitor and a 0.22µF output
capacitor are sufficient for most LT1937 applications.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER
PHONE
URL
Taiyo Yuden
408-573-4150
www.t-yuden.com
AVX
843-448-9411
www.avxcorp.com
Murata
814-237-1431
www.murata.com
Kemet
408-986-0424
www.kemet.com
Diode Selection
Schottky diodes, with their low forward voltage drop and
fast reverse recovery, are the ideal choices for LT1937
applications. The forward voltage drop of a Schottky diode
represents the conduction losses in the diode, while the
diode capacitance (CT or CD) represents the switching
losses. For diode selection, both forward voltage drop and
diode capacitance need to be considered. Schottky diodes
with higher current ratings usually have lower forward
voltage drop and larger diode capacitance, which can
cause significant switching losses at the 1.2MHz switch-
ing frequency of the LT1937. A Schottky diode rated at
100mA to 200mA is sufficient for most LT1937 applica-
tions. Some recommended Schottky diodes are listed in
Table 3.
Table 3. Recommended Schottky Diodes
FORWARD VOLTAGE DIODE
PART
CURRENT DROP CAPACITANCE
NUMBER (mA)
(V)
(pF) MANUFACTURER
CMDSH-3 100 0.58 at
7.0 at Central
100mA
10V 631-435-1110
www.centralsemi.com
CMDSH2-3 200 0.49 at
15 at Central
200mA
10V 631-435-1110
www.centralsemi.com
BAT54
200 0.53 at
10 at Zetex
100mA
25V 631-543-7100
www.zetex.com
1937f
5
5 Page 
PACKAGE DESCRIPTIO
0.62
MAX
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
0.95
REF
1.22 REF
2.90 BSC
(NOTE 4)
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC
1.50 – 1.75
(NOTE 4)
LT1937
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.20 BSC
DATUM ‘A’
PIN ONE
0.95 BSC
0.80 – 0.90
1.00 MAX
0.30 – 0.50 REF
0.09 – 0.20
NOTE:
(NOTE 3)
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
SC6 Package
6-Lead Plastic SC70
(Reference LTC DWG # 05-08-1638)
0.47 0.65
MAX REF
1.90 BSC
1.80 – 2.20
(NOTE 4)
1.16 REF
3.26 MAX 2.1 REF
0.96 MIN
1.80 – 2.40 1.15 – 1.35
(NOTE 4)
INDEX AREA
(NOTE 6)
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
0.01 – 0.10
S5 TSOT-23 0302
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.10 – 0.40
PIN 1
0.65 BSC
0.80 – 1.00
1.00 MAX
0.15 – 0.30
6 PLCS (NOTE 3)
0.00 – 0.10
0.10 – 0.30
0.10 – 0.18
NOTE:
(NOTE 3)
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. DETAILS OF THE PIN 1 INDENTIFIER ARE OPTIONAL,
BUT MUST BE LOCATED WITHIN THE INDEX AREA
7. EIAJ PACKAGE REFERENCE IS EIAJ SC-70
SC6 SC70 0302
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.
1937f
11
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| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet LT1937ESC6.PDF ] | |
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