LT3475 Datasheet, PDF (1/20 Pages) Linear Technology – Dual Step-Down l 1.5A LED Driver

LT3475/LT3475-1
Dual Step-Down
1.5A LED Driver
FEATURES
■ _{True Color PWM}^TM _{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 Surfac_Ue Mount Package
APPLICATIO S
■ _{Automotive and Avionic Lighting}
■ _{Architectural Detail Lighting}
■ _{Display Backlighting}
■ _{Constant-Current Sources}
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Patents Pending.
DESCRIPTIO
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 al-
lows 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, avoid-
ing 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 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.
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.
TYPICAL APPLICATIO
Dual Step-Down 1.5A LED Driver
V_IN
5V TO 36V
4.7μF
0.22μF
10μH
V_IN
BOOST1
SHDN
BOOST2
LT3475
SW1
SW2
0.22μF
10μH
2.2μF
*DIMMING
CONTROL
0.1μF
1.5A LED
CURRENT
OUT1
LED1
OUT2
LED2
PWM1
V_C1
REF
V_ADJ1
GND
PWM2
V_C2
R_T
V_ADJ2
DIMMING*
CONTROL
24.3k
0.1μF
1.5A LED
CURRENT
2.2μF
*SEE APPLICATIONS SECTION FOR DETAILS
f_SW = 600kHz
3475 TA01
Efficiency
95 _{VIN = 12V}
90
TWO SERIES CONNECTED
WHITE 1.5A LEDS
85
80
SINGLE WHITE 1.5A LED
75
70
65
60
55
0
0.5
1
LED CURRENT (A)
1.5
3475 TA01b
3475fb
1