LT3474/LT3474-1
Step-Down
1A LED Driver
FEATURES
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DESCRIPTION
The LT
®
3474/LT3474-1 are fixed 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.
True Color PWM™ Delivers Constant Color with
400:1 Dimming Range
Wide Input Range: 4V to 36V
Up to 1A LED Current
Adjustable 200kHz–2MHz Switching Frequency
Adjustable Control of LED Current
Integrated Boost Diode
High Output Current Accuracy is Maintained
Over a Wide Range from 35mA to 1A
Open LED (LT3474) and Short-Circuit Protection
High Side Sense Allows Grounded
Cathode Connection
Uses Small Inductors and Ceramic Capacitors
LT3474-1 Drives LED Strings Up to 26V
Compact 16-Lead TSSOP Thermally Enhanced
Surface Mount Package
APPLICATIONS
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Automotive and Avionic Lighting
Architectural Detail Lighting
Display Backlighting
Constant Current Sources
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
V
IN
5V TO 36V
2.2μF
V
IN
SHDN
LT3474
R
T
REF
80.6k
0.1μF
V
ADJ
V
C
GND
LED1
55
*SEE APPLICATIONS SECTION FOR DETAILS
3474 TA01a
Efficiency
95
0.22μF
EFFICIENCY (%)
10μH
90
85
80
ONE WHITE 1A LED
75
70
65
60
0
200
800
600
LED CURRENT (mA)
400
1000
3474 G02
V
IN
= 12V
TWO SERIES CONNECTED
WHITE 1A LEDS
BOOST
SW
BIAS
OUT
PWM
LED
DIMMING*
CONTROL
2.2μF
3474fd
1
LINER [ LINEAR TECHNOLOGY ]
