Datasheet LT3478, LT3478-1 (Analog Devices)
| Manufacturer | Analog Devices |
| Description | 4.5A Monolithic LED Drivers with True Color PWM Dimming |
| Pages / Page | 24 / 1 — FEATURES. DESCRIPTIO. True Color PWM™ Dimming Delivers Constant LED. … |
| File Format / Size | PDF / 295 Kb |
| Document Language | English |
FEATURES. DESCRIPTIO. True Color PWM™ Dimming Delivers Constant LED. Color with Up to 3000:1 Range
Model Line for this Datasheet
Text Version of Document
LT3478/LT3478-1 4.5A Monolithic LED Drivers with True Color PWM Dimming
U FEATURES DESCRIPTIO
■
True Color PWM™ Dimming Delivers Constant LED
The LT®3478/LT3478-1 are 4.5A step-up DC/DC convert-
Color with Up to 3000:1 Range
ers designed to drive LEDs with a constant current over ■
Wide Input Voltage Range: 2.8V to 36V
a wide programmable range. Series connection of the ■
4.5A, 60m
Ω
, 42V Internal Switch
LEDs provides identical LED currents for uniform bright- ■
Drives LEDs in Boost, Buck-Boost or Buck Modes
ness without the need for ballast resistors and expensive ■
Integrated Resistors for Inductor and LED Current
factory calibration.
Sensing
The LT3478-1 reduces external component count and cost ■
Program LED Current:
by integrating the LED current sense resistor. The LT3478
100mA to 1050mA (LT3478-1)
uses an external sense resistor to extend the maximum
(10mV to 105mV)/RSENSE (LT3478)
programmable LED current beyond 1A and also to achieve ■
Program LED Current De-Rating vs Temperature
greater accuracy when programming low LED currents. ■
Separate Inductor Supply Input
Operating frequency can be set with an external resistor ■ Inrush Current Protection from 200kHz up to 2.25MHz. Unique circuitry allows a ■ Programmable Soft-Start PWM dimming range up to 3000:1 while maintaining ■ Fixed Frequency Operation from 200kHz to 2.25MHz constant LED color. The LT3478/LT3478-1 are ideal for ■ Open LED Protection (Programmable OVP) high power LED driver applications such as automotive TFT ■ Accurate Shutdown/UVLO Threshold with LCD backlights, courtesy lighting and heads-up displays. Programmable Hysteresis One of two CTRL pins can be used to program maximum ■ 16-Pin Thermally Enhanced TSSOP Package LED current. The other CTRL pin can be used to program
U
a reduction in maximum LED current vs temperature to
APPLICATIO S
maximize LED usage and improve reliability. ■ High Power LED Driver Additional features include inrush current protection, ■ Automotive Lighting programmable open LED protection and programmable , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. soft-start. Each part is available in a 16-pin thermally All other trademarks are the property of their respective owners. Patents Pending. enhanced TSSOP Package.
U TYPICAL APPLICATIO Automotive TFT LCD Backlight Effi ciency vs VIN
100 V 10µH IN 8V TO 16V ILED = 700mA fOSC = 500kHz 10µF 4.7µF PWM DUTY CYCLE = 100% VIN VS L SW 95 SHDN OUT VREF 0.1Ω R 45.3k SENSE 90 CTRL2 LT3478-1 LED (LT3478) OVPSET EFFICIENCY (%) 54.9k 85 CTRL1 700mA 15W 130k PWM SS VC RT 6 LEDs 6 LEDs LUXEON III (WHITE) 80 (WHITE) 8 10 12 14 16 1µF 0.1µF 69.8k VIN (V) PWM DIMMING 3478 TA01b CONTROL 3478 TA01 34781f 1
U FEATURES DESCRIPTIO
■
True Color PWM™ Dimming Delivers Constant LED
The LT®3478/LT3478-1 are 4.5A step-up DC/DC convert-
Color with Up to 3000:1 Range
ers designed to drive LEDs with a constant current over ■
Wide Input Voltage Range: 2.8V to 36V
a wide programmable range. Series connection of the ■
4.5A, 60m
Ω
, 42V Internal Switch
LEDs provides identical LED currents for uniform bright- ■
Drives LEDs in Boost, Buck-Boost or Buck Modes
ness without the need for ballast resistors and expensive ■
Integrated Resistors for Inductor and LED Current
factory calibration.
Sensing
The LT3478-1 reduces external component count and cost ■
Program LED Current:
by integrating the LED current sense resistor. The LT3478
100mA to 1050mA (LT3478-1)
uses an external sense resistor to extend the maximum
(10mV to 105mV)/RSENSE (LT3478)
programmable LED current beyond 1A and also to achieve ■
Program LED Current De-Rating vs Temperature
greater accuracy when programming low LED currents. ■
Separate Inductor Supply Input
Operating frequency can be set with an external resistor ■ Inrush Current Protection from 200kHz up to 2.25MHz. Unique circuitry allows a ■ Programmable Soft-Start PWM dimming range up to 3000:1 while maintaining ■ Fixed Frequency Operation from 200kHz to 2.25MHz constant LED color. The LT3478/LT3478-1 are ideal for ■ Open LED Protection (Programmable OVP) high power LED driver applications such as automotive TFT ■ Accurate Shutdown/UVLO Threshold with LCD backlights, courtesy lighting and heads-up displays. Programmable Hysteresis One of two CTRL pins can be used to program maximum ■ 16-Pin Thermally Enhanced TSSOP Package LED current. The other CTRL pin can be used to program
U
a reduction in maximum LED current vs temperature to
APPLICATIO S
maximize LED usage and improve reliability. ■ High Power LED Driver Additional features include inrush current protection, ■ Automotive Lighting programmable open LED protection and programmable , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. soft-start. Each part is available in a 16-pin thermally All other trademarks are the property of their respective owners. Patents Pending. enhanced TSSOP Package.
U TYPICAL APPLICATIO Automotive TFT LCD Backlight Effi ciency vs VIN
100 V 10µH IN 8V TO 16V ILED = 700mA fOSC = 500kHz 10µF 4.7µF PWM DUTY CYCLE = 100% VIN VS L SW 95 SHDN OUT VREF 0.1Ω R 45.3k SENSE 90 CTRL2 LT3478-1 LED (LT3478) OVPSET EFFICIENCY (%) 54.9k 85 CTRL1 700mA 15W 130k PWM SS VC RT 6 LEDs 6 LEDs LUXEON III (WHITE) 80 (WHITE) 8 10 12 14 16 1µF 0.1µF 69.8k VIN (V) PWM DIMMING 3478 TA01b CONTROL 3478 TA01 34781f 1
