LT3474_15 Datasheet, PDF (1/20 Pages) Linear Technology – Step-Down 1A LED Driver

LT3474/LT3474-1
Step-Down
1A LED Driver
FEATURES
n _{True Color PWM™ Delivers Constant Color with}
400:1 Dimming Range
n _{Wide Input Range: 4V to 36V}
n _{Up to 1A LED Current}
n _{Adjustable 200kHz–2MHz Switching Frequency}
n _{Adjustable Control of LED Current}
n _{Integrated Boost Diode}
n _{High Output Current Accuracy is Maintained}
Over a Wide Range from 35mA to 1A
n _{Open LED (LT3474) and Short-Circuit Protection}
n _{High Side Sense Allows Grounded}
Cathode Connection
n _{Uses Small Inductors and Ceramic Capacitors}
n _{LT3474-1 Drives LED Strings Up to 26V}
n _{Compact 16-Lead TSSOP Thermally Enhanced}
Surface Mount Package
APPLICATIONS
■ _{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
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.
TYPICAL APPLICATION
Step-Down 1A LED Driver
V_IN
5V TO 36V
2.2μF
80.6k
0.1μF
V_IN
BOOST
SHDN
SW
LT3474
R_T
BIAS
REF
OUT
V_ADJ
PWM
V_C
LED
GND
0.22μF
10μH
DIMMING*
CONTROL
LED1
2.2μF
*SEE APPLICATIONS SECTION FOR DETAILS
3474 TA01a
95
V_IN = 12V
90
Efficiency
TWO SERIES CONNECTED
WHITE 1A LEDS
85
80
ONE WHITE 1A LED
75
70
65
60
55
0
200 400 600 800 1000
LED CURRENT (mA)
3474 G02
3474fd
1