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LT3590

3590f

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

48V Buck Mode

LED Driver in SC70

and 2mm x 2mm DFN

The LT

3590 is a ﬁ xed frequency buck mode converter

speciﬁ cally designed to drive up to 10 LEDs in series from

a 48V DC source. Series connection of the LEDs provides

identical LED currents of up to 50mA, resulting in uniform

brightness and eliminating the need for ballast resistors.

A ﬁ xed frequency, current mode architecture results in

stable operation over a wide range of input voltage and

output voltage.

The high switching frequency of 850kHz permits the use

of tiny, low proﬁ le inductors and capacitors. A single pin

performs both shutdown and accurate LED dimming

control. The power switch, Schottky diode and control

circuitry are all contained inside a space saving SC70

package or 2mm × 2mm DFN package to allow a small

converter footprint and lower parts cost.

Buck Mode Driver for Ten White LEDs

■

4.5V to 55V Input Voltage Range

■

Up to 50mA LED Current

■

80mA, 55V Switch

■

Internal Schottky Diode

■

15μA Supply Current in Shutdown

■

500μA Supply Current Operating, Not Switching

■

Switching Frequency: 850kHz

■

200mV Feedback Voltage with ±5% Accuracy

■

CTRL Input Performs Dimming and Shutdown

■

91% Efﬁ ciency (10 LEDs, 50mA)

■

Requires Only 1μF Output Capacitor

■

8-Lead SC70 Package

■

6-Lead 2mm × 2mm DFN Package

■

LED Fixed Signage

■

Trafﬁ c Signs

■

Neon Sign Replacement

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

48V

CONTROL

CTRL

4Ω

50mA

LT3590

VREG SW

LED

GND

1μF

0.1μF

1μF

3590 TA01a

470μH

Conversion Efﬁ ciency

LED CURRENT (mA)

EFFICIENCY (%)

10 20 40

100

3590 TA01b

Summary of content (16 pages)

PAGE 1
LT3590 48V Buck Mode LED Driver in SC70 and 2mm x 2mm DFN DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 4.
PAGE 2
LT3590 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage (VIN) ..................................... –0.3V to 55V LED Voltage ............................................... –0.3V to 55V CTRL Voltage ................................................. 0V to 6.0V VREG Voltage ................................................. 0V to 4.0V Operating Junction Temperature Range (Note 2) ...............................................– 40°C to 85°C Maximum Junction Temperature...........................
PAGE 3
LT3590 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C, VIN = 48V, VCTRL = 3.3V, unless otherwise noted. PARAMETER CONDITIONS MIN Minimum Operating Voltage TYP MAX UNITS 200 210 mV 4.5 ● LED Current Sense Voltage (VIN - VLED) Sense Voltage Load Regulation ΔILED = 10mA to 50mA Quiescent Current ON, No Switching VLED = 47.
PAGE 4
LT3590 TYPICAL PERFORMANCE CHARACTERISTICS Switch Saturation Voltage (VCESAT) 0.7 –40°C 0.6 125°C 0.5 25°C 0.4 0.3 VCTRL = 0V TA = 25°C 1.1 1.0 25°C –40°C 0.9 0.8 125°C 0.7 0.6 0.4 20 60 40 80 SWITCH CURRENT (mA) 100 16 14 12 0 Quiescent Current 14 12 550 50 75 25 TEMPERATURE (°C) 100 125 50 40 60 500 450 1.5 VIN = 48V 1.0 VIN = 24V 0.5 400 0 30 VIN (V) Schottky Leakage Current SCHOTTKY LEAKAGE CURRENT (μA) QUIESCENT CURRENT (μA) 16 20 10 2.0 VCTRL = 3.
PAGE 5
LT3590 TYPICAL PERFORMANCE CHARACTERISTICS Sense Voltage (VIN – VLED) vs VCTRL 150 0.20 0.15 0.10 0.05 0 Switching Current Limit vs Temperature 150 TA = 25°C 140 130 120 110 100 90 1 0.5 0 2 1.
PAGE 6
LT3590 PIN FUNCTIONS (SC70/DFN) SW (Pin 1/Pin 3): Switch Pin. Minimize trace area at this pin to minimize EMI. Connect the inductor at this pin. VREG (Pin 6/Pin 6): Internally Generated 3.3V Regulated Output Pin. Must be locally bypassed with a 0.1μF X5R capacitor. GND (Pins 2, 3, 4/Pin 2): Ground Pins. All ground pins should be tied directly to local ground plane. Proper soldering of these pins to the PCB ground is required to achieve the rated thermal performance.
PAGE 7
LT3590 OPERATION The LT3590 uses a constant-frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the Block Diagram. The maximum input voltage is limited by the absolute maximum VIN rating of 55V. At power-up, the bandgap reference, the start-up bias, and the regulator are turned on.
PAGE 8
LT3590 APPLICATIONS INFORMATION Inductor Selection Capacitor Selection A 220μH inductor is recommended for most LT3590 applications with VIN < 25V and 470μH is recommended for applications with VIN > 25V. Although small size and high efﬁciency are major concerns, the inductor should have low core losses at 850kHz and low DCR (copper wire resistance). Several manufacturers and inductor series that meet these criteria are listed in Table 1.
PAGE 9
LT3590 APPLICATIONS INFORMATION Programming LED Current Using a DC Voltage The feedback resistor (R1 in Figure 1) and the sense voltage (VIN - VLED) control the LED current. For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The CTRL pin voltage can be modulated to set the dimming of the LED string. As the voltage on the CTRL pin increases from 0V to 1.5V, the LED current increases from 0 to ILED.
PAGE 10
LT3590 APPLICATIONS INFORMATION Direct PWM Dimming Changing the forward current ﬂowing in the LEDs not only changes the intensity of the LEDs, it also changes the color. The chromaticity of the LEDs changes with the change in forward current. Many applications cannot tolerate any shift in the color of the LEDs. Controlling the intensity of the LEDs with a direct PWM signal allows dimming of the LEDs without changing the color. In addition, direct PWM dimming offers a wider dimming range to the user.
PAGE 11
LT3590 APPLICATIONS INFORMATION The dimming range can be further extended by changing the amplitude of the PWM signal. The height of the PWM signal sets the commanded sense voltage across the sense resistor through the CTRL pin. In this manner both analog dimming and direct PWM dimming extend the dimming range for a given application. The color of the LEDs no longer remains constant because the forward current of the LED changes with the height of the CTRL signal.
PAGE 12
LT3590 TYPICAL APPLICATIONS 48V Supply for 6 LED String, 50mA Current Conversion Efﬁciency 100 C2 1μF 90 R1 4Ω 6 LEDs C1 1μF VIN CONTROL >1.5V LED L1 470μH CTRL EFFICIENCY (%) VIN 48V 50mA LT3590 70 60 50 VREG C3 0.1μF 80 SW 3590 TA02a 40 GND 10 0 20 30 LED CURRENT (mA) 40 50 3590 TA02b L1: MURATA LQH32CN221K03 48V Supply for 5 LED String, 30mA Current Conversion Efﬁciency 100 C2 1μF 90 R1 6.8Ω C1 1μF VIN CONTROL >1.
PAGE 13
LT3590 TYPICAL APPLICATIONS 12V or 24V Supply for a Single LED, 50mA Current Conversion Efﬁciency 80 C2 2.2μF 75 R1 4Ω C1 1μF VIN CONTROL >1.5V LED L1 220μH CTRL VREG 65 24V 60 55 50 LT3590 45 SW C3 0.1μF 12V 70 EFFICIENCY (%) VIN 12V OR 24V 50mA 3590 TA05a 40 GND 0 10 20 30 LED CURRENT (mA) 40 50 3590 TA05b 48V Supply for Two Strings of 10 LEDs, 25mA Current Conversion Efﬁciency 100 C2 1μF 90 EFFECIENCY (%) 25mA R1 4Ω 25mA VIN 48V C1 1μF 80 70 60 50 VIN CONTROL >1.
PAGE 14
LT3590 PACKAGE DESCRIPTION DC Package 6-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1703) R = 0.115 TYP 0.56 ± 0.05 (2 SIDES) 0.675 ±0.05 2.50 ±0.05 1.15 ±0.05 0.61 ±0.05 (2 SIDES) PACKAGE OUTLINE PIN 1 BAR TOP MARK (SEE NOTE 6) 0.38 ± 0.05 4 2.00 ±0.10 (4 SIDES) PIN 1 CHAMFER OF EXPOSED PAD 3 0.25 ± 0.05 0.50 BSC 1.42 ±0.05 (2 SIDES) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 6 0.75 ±0.05 1 (DC6) DFN 1103 0.25 ± 0.05 0.50 BSC 1.37 ±0.05 (2 SIDES) 0.00 – 0.
PAGE 15
LT3590 PACKAGE DESCRIPTION SC8 Package 8-Lead Plastic SC70 (Reference LTC DWG # 05-08-1639 Rev Ø) 0.30 MAX 0.50 REF PIN 8 1.80 – 2.20 (NOTE 4) 1.00 REF INDEX AREA (NOTE 6) 1.80 – 2.40 1.15 – 1.35 (NOTE 4) 2.8 BSC 1.8 REF PIN 1 RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.10 – 0.40 0.50 BSC 0.15 – 0.27 8 PLCS (NOTE 3) 0.80 – 1.00 0.00 – 0.10 REF 1.00 MAX GAUGE PLANE 0.15 BSC 0.26 – 0.46 SC8 SC70 0905 REV Ø 0.10 – 0.18 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2.
PAGE 16
LT3590 TYPICAL APPLICATION Conversion Efﬁciency 24V Supply for 6 LED String, 50mA Current C2 1μF 100 95 R1 4Ω C1 1μF CONTROL >1.5V VIN 90 LED L1 220μH CTRL LT3590 VREG C3 0.1μF EFFICIENCY (%) VIN 24V 50mA 85 80 75 70 65 SW 3590 TA08a GND 60 0 L1: MURATA LQH32CN-221 10 20 30 LED CURRENT (mA) 40 50 3590 TA08b RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1932 Constant Current, 1.2MHz, High Efﬁciency White LED Boost Regulator VIN: 1.0V to 10.