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PDF LT1932 Data sheet ( Hoja de datos )
| Número de pieza | LT1932 | |
| Descripción | Constant-Current DC/DC LED Driver in ThinSOT | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LT1932 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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FEATURES
s Up to 80% Efficiency
s Inherently Matched LED Current
s Adjustable Control of LED Current
s Drives Five White LEDs from 2V
s Drives Six White LEDs from 2.7V
s Drives Eight White LEDs from 3V
s Disconnects LEDs In Shutdown
s 1.2MHz Fixed Frequency Switching
s Uses Tiny Ceramic Capacitors
s Uses Tiny 1mm-Tall Inductors
s Regulates Current Even When VIN > VOUT
s Operates with VIN as Low as 1V
s Low Profile (1mm) ThinSOTTM Package
U
APPLICATIO S
s Cellular Telephones
s Handheld Computers
s Digital Cameras
s Portable MP3 Players
s Pagers
TYPICAL APPLICATIO
Li-Ion Driver for Four White LEDs
VIN
2.7V TO 4.2V
L1
6.8µH
D1
C1
4.7µF
PWM
DIMMING
CONTROL
61
VIN SW
LT1932
5
SHDN
3
LED
RSET
GND
4
RSET
1.50k
2
15mA
C1: TAIYO YUDEN JMK212BJ475
C2: TAIYO YUDEN EMK212BJ105
D1:ZETEX ZHCS400
L1: SUMIDA CLQ4D106R8 OR PANASONIC ELJEA6R8
LT1932
Constant-Current DC/DC
LED Driver in ThinSOT
DESCRIPTIO
The LT®1932 is a fixed frequency step-up DC/DC converter
designed to operate as a constant-current source. Be-
cause it directly regulates output current, the LT1932 is
ideal for driving light emitting diodes (LEDs) whose light
intensity is proportional to the current passing through
them, not the voltage across their terminals.
With an input voltage range of 1V to 10V, the device works
from a variety of input sources. The LT1932 accurately
regulates LED current even when the input voltage is
higher than the LED voltage, greatly simplifying battery-
powered designs. A single external resistor sets LED
current between 5mA and 40mA, which can then be easily
adjusted using either a DC voltage or a pulse width
modulated (PWM) signal. When the LT1932 is placed in
shutdown, the LEDs are disconnected from the output,
ensuring a quiescent current of under 1µA for the entire
circuit. The device’s 1.2MHz switching frequency permits
the use of tiny, low profile chip inductors and capacitors to
minimize footprint and cost in space-conscious portable
applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
C2
1µF
1932 TA01
Efficiency
85
80 VIN = 4.2V
75 VIN = 2.7V
70
65
60
55
0
5 10 15
LED CURRENT (mA)
20
1932 TA02
1932f
1
1 page  
LT1932
APPLICATIO S I FOR ATIO
Inductor Selection
Several inductors that work well with the LT1932 are listed
in Table 1. Many different sizes and shapes are available.
Consult each manufacturer for more detailed information
and for their entire selection of related parts. As core
losses at 1.2MHz are much lower for ferrite cores that for
the cheaper powdered-iron ones, ferrite core inductors
should be used to obtain the best efficiency. Choose an
inductor that can handle at least 0.5A and ensure that the
inductor has a low DCR (copper wire resistance) to mini-
mize I2R power losses. A 4.7µH or 6.8µH inductor will be
a good choice for most LT1932 designs.
Table 1. Recommended Inductors
PART
MAX
L DCR
(µH) (mΩ)
ELJEA4R7
ELJEA6R8
4.7 180
6.8 250
LQH3C4R7M24
LQH3C100M24
4.7 260
10 300
LB2016B4R7
LB2016B100
4.7 250
6.8 350
CMD4D06-4R7
CMD4D06-6R8
CLQ4D10-4R7
CLQ4D10-6R8
4.7 216
6.8 296
4.7 162
6.8 195
MAX
HEIGHT
(mm)
2.2
2.2
2.2
2.2
1.6
1.6
0.8
0.8
1.2
1.2
VENDOR
Panasonic
(714) 373-7334
www.panasonic.com
Murata
(814) 237-1431
www.murata.com
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
Sumida
(847) 956-0666
www.sumida.com
Inductor Efficiency Considerations
Many applications have thickness requirements that re-
strict component heights to 1mm or 2mm. There are 2mm
tall inductors currently available that provide a low DCR
and low core losses that help provide good overall effi-
ciency. Inductors with a height of 1mm (and less) are
becoming more common, and a few companies have
introduced chip inductors that are not only thin, but have
a very small footprint as well. While these smaller induc-
tors will be a necessity in some designs, their smaller size
gives higher DCR and core losses, resulting in lower
efficiencies. Figure 2 shows efficiency for the Typical
Application circuit on the front page of this data sheet, with
several different inductors. The larger devices improve
efficiency by up to 12% over the smaller, thinner ones.
Keep this in mind when choosing an inductor.
The value of inductance also plays an important role in the
overall system efficiency. While a 1µH inductor will have
a lower DCR and a higher current rating than the 6.8µH
version of the same part, lower inductance will result in
higher peak currents in the switch, inductor and diode.
Efficiency will suffer if inductance is too small. Figure 3
shows the efficiency of the Typical Application on the front
page of this data sheet, with several different values of the
same type of inductor (Panasonic ELJEA). The smaller
values give an efficiency 3% to 5% lower than the 6.8µH
value.
85
80
SUMIDA
CLQ4D10-6R8
75
70
PANASONIC
ELJEA6R8
SUMIDA
CMD4D06-6R8
65 TAIYO YUDEN
LB2016B6R8
60
TAIYO YUDEN
LB2012B6R8
55
0 5 10
VIN = 3.6V
4 WHITE LEDs
ALL ARE 10µH
INDUCTORS
15 20
LED CURRENT (mA)
1932 F02
Figure 2. Efficiency for Several Different Inductor Types
85
80
6.8µH
75 22µH
4.7µH
70
2.2µH
65
60
55
0
VIN = 3.6V
4 WHITE LEDs
PANASONIC ELJEA
INDUCTORS
5 10 15
LED CURRENT (mA)
20
1932 F03
Figure 3. Efficiency for Several Different Inductor Values
1932f
5
5 Page 
TYPICAL APPLICATIO S
2-Cell Driver for Two White LEDs
VIN
1.8V TO 3V
L1
4.7µH
D1
C1
4.7µF
2.5V DC
DIMMING
CONTROL
61
VIN SW
LT1932
5
SHDN
3
LED
RSET GND 15mA
60.4k 4
2
RSET
1.50k
C1: TAIYO YUDEN JMK212BJ475
C2: TAIYO YUDEN LMK212BJ225
D1: ZETEX ZHCS400
L1: MURATA LQH3C4R7M24
(408) 573-4150
(408) 573-4150
(631) 543-7100
(814) 237-1431
C2
2.2µF
1932 TA15a
2-Cell Driver for Three White LEDs
VIN
1.8V TO 3V
L1
4.7µH
D1
C1
4.7µF
2.5V DC
DIMMING
CONTROL
61
VIN SW
LT1932
5
SHDN
3
LED
RSET GND 15mA
60.4k 4
2
RSET
1.50k
C1: TAIYO YUDEN JMK212BJ475
C2: TAIYO YUDEN EMK316BJ225
D1: ZETEX ZHCS400
L1: MURATA LQH3C4R7M24
(408) 573-4150
(408) 573-4150
(631) 543-7100
(814) 237-1431
C2
2.2µF
1932 TA06a
LT1932
85
80
75
70
65
60
55
0
Efficiency
VIN = 3V
VIN = 1.8V
5 10 15
LED CURRENT (mA)
20
1932 TA15b
Efficiency
85
80
75
70
65
60
55
0
VIN = 3V
VIN = 1.8V
5 10 15
LED CURRENT (mA)
20
1932 TA06b
1932f
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1932.PDF ] | |
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