LT3475/LT3475-1
Dual Step-Down
1.5A LED Driver
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DESCRIPTIO
FEATURES
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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 Surface Mount Package
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 allows 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, avoiding the color shift normally associated with LED current
dimming.
The high switching frequency offers several advantages,
permitting the use of small inductors and ceramic capacitors. 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.
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APPLICATIO S
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Automotive and Avionic Lighting
Architectural Detail Lighting
Display Backlighting
Constant-Current Sources
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.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Patents Pending.
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TYPICAL APPLICATIO
Dual Step-Down 1.5A LED Driver
Efficiency
VIN
5V TO 36V
4.7μF
BOOST2
SW1
10μH
2.2μF
0.1μF
1.5A LED
CURRENT
85
SW2
OUT1
LED1
*DIMMING
CONTROL
OUT2
LED2
PWM1
PWM2
VC1
VC2
REF
DIMMING*
CONTROL
RT
VADJ1
24.3k
1.5A LED
CURRENT
SINGLE WHITE 1.5A LED
75
70
fSW = 600kHz
60
55
3475 TA01
*SEE APPLICATIONS SECTION FOR DETAILS
80
65
2.2μF
0.1μF
VADJ2
GND
TWO SERIES CONNECTED
WHITE 1.5A LEDS
0.22μF
LT3475
10μH
VIN = 12V
90
EFFICIENCY (%)
0.22μF
95
SHDN
VIN
BOOST1
0
0.5
1
1.5
LED CURRENT (A)
3475 TA01b
3475fb
1