Datasheet LT3474, LT3474-1 (Analog Devices)
| Hersteller | Analog Devices |
| Beschreibung | Step-Down 1A LED Driver |
| Seiten / Seite | 20 / 1 — FEATURES. DESCRIPTION. True Color PWM™ Delivers Constant Color with. … |
| Dateiformat / Größe | PDF / 226 Kb |
| Dokumentensprache | Englisch |
FEATURES. DESCRIPTION. True Color PWM™ Delivers Constant Color with. 400:1 Dimming Range. Wide Input Range: 4V to 36V
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LT3474/LT3474-1 Step-Down 1A LED Driver
FEATURES DESCRIPTION
n
True Color PWM™ Delivers Constant Color with
The LT®3474/LT3474-1 are fi xed frequency step-down
400:1 Dimming Range
DC/DC converters designed to operate as constant-current n
Wide Input Range: 4V to 36V
sources. An internal sense resistor monitors the output n
Up to 1A LED Current
current allowing accurate current regulation, ideal for n
Adjustable 200kHz–2MHz Switching Frequency
driving high current LEDs. High output current accuracy n
Adjustable Control of LED Current
is maintained over a wide current range, from 35mA to n
Integrated Boost Diode
1A, allowing a wide dimming range. n
High Output Current Accuracy is Maintained
Unique PWM circuitry allows a dimming range of 400:1,
Over a Wide Range from 35mA to 1A
avoiding the color shift normally associated with LED n
Open LED (LT3474) and Short-Circuit Protection
current dimming. n
High Side Sense Allows Grounded
The high switching frequency offers several advantages,
Cathode Connection
n permitting the use of small inductors and ceramic capaci-
Uses Small Inductors and Ceramic Capacitors
tors. Small inductors combined with the 16-lead TSSOP n
LT3474-1 Drives LED Strings Up to 26V
surface mount package save space and cost versus n Compact 16-Lead TSSOP Thermally Enhanced alternative solutions. The constant switching frequency Surface Mount Package combined with low-impedance ceramic capacitors result in low, predictable output ripple.
APPLICATIONS
With their wide input range of 4V to 36V, the LT3474/ ■ Automotive and Avionic Lighting LT3474-1 regulate a broad array of power sources, from ■ Architectural Detail Lighting 5V logic rails to unregulated wall transformers, lead acid ■ Display Backlighting batteries and distributed power supplies. A current mode ■ Constant Current Sources PWM architecture provides fast transient response and L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. cycle-by-cycle current limiting. Frequency foldback and True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patent Pending thermal shutdown provide additional protection.
TYPICAL APPLICATION Step-Down 1A LED Driver Effi ciency
VIN 95 5V TO 36V VIN = 12V TWO SERIES CONNECTED 90 WHITE 1A LEDS V 0.22μF 2.2μF IN BOOST 85 SHDN SW LT3474 10μH 80 ONE WHITE 1A LED R BIAS T 75 REF OUT 70 V EFFICIENCY (%) ADJ PWM DIMMING* 80.6k CONTROL 2.2μF 65 V LED C 0.1μF GND 60 LED1 55 0 200 400 600 800 1000 *SEE APPLICATIONS SECTION FOR DETAILS LED CURRENT (mA) 3474 TA01a 3474 G02 3474fd 1
FEATURES DESCRIPTION
n
True Color PWM™ Delivers Constant Color with
The LT®3474/LT3474-1 are fi xed frequency step-down
400:1 Dimming Range
DC/DC converters designed to operate as constant-current n
Wide Input Range: 4V to 36V
sources. An internal sense resistor monitors the output n
Up to 1A LED Current
current allowing accurate current regulation, ideal for n
Adjustable 200kHz–2MHz Switching Frequency
driving high current LEDs. High output current accuracy n
Adjustable Control of LED Current
is maintained over a wide current range, from 35mA to n
Integrated Boost Diode
1A, allowing a wide dimming range. n
High Output Current Accuracy is Maintained
Unique PWM circuitry allows a dimming range of 400:1,
Over a Wide Range from 35mA to 1A
avoiding the color shift normally associated with LED n
Open LED (LT3474) and Short-Circuit Protection
current dimming. n
High Side Sense Allows Grounded
The high switching frequency offers several advantages,
Cathode Connection
n permitting the use of small inductors and ceramic capaci-
Uses Small Inductors and Ceramic Capacitors
tors. Small inductors combined with the 16-lead TSSOP n
LT3474-1 Drives LED Strings Up to 26V
surface mount package save space and cost versus n Compact 16-Lead TSSOP Thermally Enhanced alternative solutions. The constant switching frequency Surface Mount Package combined with low-impedance ceramic capacitors result in low, predictable output ripple.
APPLICATIONS
With their wide input range of 4V to 36V, the LT3474/ ■ Automotive and Avionic Lighting LT3474-1 regulate a broad array of power sources, from ■ Architectural Detail Lighting 5V logic rails to unregulated wall transformers, lead acid ■ Display Backlighting batteries and distributed power supplies. A current mode ■ Constant Current Sources PWM architecture provides fast transient response and L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. cycle-by-cycle current limiting. Frequency foldback and True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patent Pending thermal shutdown provide additional protection.
TYPICAL APPLICATION Step-Down 1A LED Driver Effi ciency
VIN 95 5V TO 36V VIN = 12V TWO SERIES CONNECTED 90 WHITE 1A LEDS V 0.22μF 2.2μF IN BOOST 85 SHDN SW LT3474 10μH 80 ONE WHITE 1A LED R BIAS T 75 REF OUT 70 V EFFICIENCY (%) ADJ PWM DIMMING* 80.6k CONTROL 2.2μF 65 V LED C 0.1μF GND 60 LED1 55 0 200 400 600 800 1000 *SEE APPLICATIONS SECTION FOR DETAILS LED CURRENT (mA) 3474 TA01a 3474 G02 3474fd 1