LT3474/LT3474-1
1
3474fd
The LT
®
3474/LT3474-1 are fi xed frequency step-down
DC/DC converters designed to operate as constant-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.
Unique PWM circuitry allows a dimming range of 400:1,
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 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.
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
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Constant Current Sources
n
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
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Adjustable 200kHz–2MHz Switching Frequency
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Adjustable Control of LED Current
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Integrated Boost Diode
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High Output Current Accuracy is Maintained
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
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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
TYPICAL APPLICATION
DESCRIPTION
Step-Down
1A LED Driver
Step-Down 1A LED Driver
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
FEATURES
APPLICATIONS
Effi ciency
V
IN
BIAS
OUT
PWM
LED
LED1
DIMMING*
CONTROL
LT3474
0.1μF
V
IN
5V TO 36V
2.2μF
0.22μF
10μH
3474 TA01a
80.6k
*SEE APPLICATIONS SECTION FOR DETAILS
SHDN
REF
BOOST
SW
V
ADJ
R
T
V
C
GND
2.2μF
LED CURRENT (mA)
0
EFFICIENCY (%)
70
75
80
600
1000
3474 G02
65
60
55
200 400 800
85
90
95
TWO SERIES CONNECTED
WHITE 1A LEDS
ONE WHITE 1A LED
V
IN
= 12V