LT3474/LT3474-1
Step-Down
1A LED Driver
FEATURES
DESCRIPTION
The LT®3474/LT3474-1 are fixed frequency step-down
DC/DCconvertersdesignedtooperateasconstant-current
sources. An internal sense resistor monitors the output
current allowing accurate current regulation, ideal for
driving high current LEDs. High output current accuracy
is maintained over a wide current range, from 35mA to
1A, allowing a wide dimming range.
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True Color PWM™ Delivers Constant Color with
400:1 Dimming Range
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Wide Input Range: 4V to 36V
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Up to 1A LED Current
Adjustable 200kHz–2MHz Switching Frequency
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Adjustable Control of LED Current
Integrated Boost Diode
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High Output Current Accuracy is Maintained
Unique PWM circuitry allows a dimming range of 400:1,
avoiding the color shift normally associated with LED
current dimming.
Over a Wide Range from 35mA to 1A
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Open LED (LT3474) and Short-Circuit Protection
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High Side Sense Allows Grounded
Cathode Connection
The high switching frequency offers several advantages,
permitting the use of small inductors and ceramic capaci-
tors. Small inductors combined with the 16-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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Uses Small Inductors and Ceramic Capacitors
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LT3474-1 Drives LED Strings Up to 26V
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Compact 16-Lead TSSOP Thermally Enhanced
Surface Mount Package
APPLICATIONS
With their wide input range of 4V to 36V, the LT3474/
LT3474-1 regulate a broad array of power sources, from
5V logic rails to unregulated wall transformers, lead acid
batteries and distributed power supplies. A current mode
PWM architecture provides fast transient response and
cycle-by-cycle current limiting. Frequency foldback and
thermal shutdown provide additional protection.
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Automotive and Avionic Lighting
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Architectural Detail Lighting
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Display Backlighting
Constant Current Sources
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L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners. Patent Pending
TYPICAL APPLICATION
Step-Down 1A LED Driver
Efficiency
95
V
IN
V
= 12V
IN
5V TO 36V
TWO SERIES CONNECTED
WHITE 1A LEDS
90
85
80
0.22μF
10μH
V
BOOST
SW
LT3474
IN
2.2μF
SHDN
ONE WHITE 1A LED
R
BIAS
OUT
T
75
70
REF
V
DIMMING*
CONTROL
PWM
ADJ
80.6k
0.1μF
2.2μF
65
60
55
V
LED
C
GND
LED1
*SEE APPLICATIONS SECTION FOR DETAILS
200
400
LED CURRENT (mA)
800
0
1000
600
3474 TA01a
3474 G02
3474fd
1