LT3475IFE-PBF Ver la hoja de datos (PDF) - Linear Technology
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LT3475IFE-PBF Datasheet PDF : 20 Pages
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LT3475/LT3475-1
Dual Step-Down
1.5A LED Driver
FEATURES
■ True Color PWMTM Delivers Constant Color with
3000:1 Dimming Range
■ Wide Input Range: 4V to 36V Operating, 40V
Maximum
■ Accurate and Adjustable Control of LED Current
from 50mA to 1.5A
■ High Side Current Sense Allows Grounded Cathode
LED Operation
■ Open LED (LT3475) and Short Circuit Protection
■ LT3475-1 Drives LED Strings Up to 25V
■ Accurate and Adjustable 200kHz to 2MHz
Switching Frequency
■ Anti-Phase Switching Reduces Ripple
■ Uses Small Inductors and Ceramic Capacitors
■ Available in the Compact 20-Lead TSSOP Thermally
Enhanced SurfacUe Mount Package
APPLICATIO S
■ Automotive and Avionic Lighting
■ Architectural Detail Lighting
■ Display Backlighting
■ Constant-Current Sources
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Patents Pending.
DESCRIPTIO
The LT®3475/LT3475-1 are dual step-down DC/DC
converters designed to operate as a constant-current
source. An internal sense resistor monitors the output
current allowing accurate current regulation ideal for
driving high current LEDs. The high side current sense al-
lows grounded cathode LED operation. High output current
accuracy is maintained over a wide current range, from
50mA to 1.5A, allowing a wide dimming range. Unique
PWM circuitry allows a dimming range of 3000:1, avoid-
ing the color shift normally associated with LED current
dimming.
The high switching frequency offers several advantages,
permitting the use of small inductors and ceramic capaci-
tors. Small inductors combined with the 20 lead TSSOP
surface mount package save space and cost versus
alternative solutions. The constant switching frequency
combined with low-impedance ceramic capacitors result
in low, predictable output ripple.
With its wide input range of 4V to 36V, the LT3475/LT3475-1
regulate a broad array of power sources. A current mode
PWM architecture provides fast transient response and
cycle-by-cycle current limiting. Frequency foldback and
thermal shutdown provide additional protection.
TYPICAL APPLICATIO
Dual Step-Down 1.5A LED Driver
VIN
5V TO 36V
4.7μF
0.22μF
10μH
VIN
BOOST1
SHDN
BOOST2
LT3475
SW1
SW2
0.22μF
10μH
2.2μF
*DIMMING
CONTROL
0.1μF
1.5A LED
CURRENT
OUT1
LED1
OUT2
LED2
PWM1
VC1
REF
VADJ1
GND
PWM2
VC2
RT
VADJ2
DIMMING*
CONTROL
24.3k
0.1μF
1.5A LED
CURRENT
2.2μF
*SEE APPLICATIONS SECTION FOR DETAILS
fSW = 600kHz
3475 TA01
Efficiency
95 VIN = 12V
90
TWO SERIES CONNECTED
WHITE 1.5A LEDS
85
80
SINGLE WHITE 1.5A LED
75
70
65
60
55
0
0.5
1
LED CURRENT (A)
1.5
3475 TA01b
3475fb
1
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