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LT3466

3466fa

Dual Full Function White LED

Step-Up Converter with

Built-In Schottky Diodes

Figure 1. Li-Ion Powered Driver for 8/8 White LEDs

■

Drives Up to 20 White LEDs (10 in Series

per Converter) from a 3.6V Supply

■

Two Independent Step-Up Converters Capable of

Driving Asymmetric LED Strings

■

Independent Dimming and Shutdown Control

of the Two LED Strings

■

Internal Schottky Diodes

■

Internal Soft-Start Eliminates Inrush Current

■

Open LED Protection (39.5V Max V

OUT

)

■

Fixed Frequency Operation Up to 2MHz

■

81% Efficiency Driving 16 White LEDs at 15mA

(Eight per Driver) from a 3.6V Supply

■

Wide Input Voltage Range: 2.7V to 24V

■

Available in 10-Pin DFN and 16-Pin Thermally

Enhanced TSSOP Packages

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

■

Main/Sub Displays

■

Digital Cameras, Sub-Notebook PCs

■

PDAs, Handheld Computers

■

Automotive

3466 is a dual full function step-up DC/DC converter

specifically designed to drive up to 20 White LEDs (10 in

series per converter) with a constant current. Series

connection of the LEDs provides identical LED currents

resulting in uniform brightness and eliminating the need

for ballast resistors and expensive factory calibration.

The two independent converters are capable of driving

asymmetric LED strings. The dimming of the two LED

strings can also be controlled independently. The LT3466

is ideal for providing backlight for main and sub-displays

in cell phones and other handheld devices.

The LT3466 operating frequency can be set with an

external resistor over a 200kHz to 2MHz range. A low

200mV feedback voltage minimizes power loss in the

current setting resistor for better efficiency. Additional

features include output voltage limiting when LEDs are

disconnected and internal soft-start.

The LT3466 is available in the 10-pin (3mm × 3mm ×

0.75mm) DFN and 16-pin thermally enhanced TSSOP

packages.

CTRL1 GND CTRL2

SW1 SW2V

3V TO 5V

47µH

1µF

2.2µF 2.2µF

LED1 LED2

47µH

LT3466

SHUTDOWN

AND DIMMING

CONTROL 2

SHUTDOWN

AND DIMMING

CONTROL 1

OUT1

FB1

10Ω 10Ω

3466 F01a

OUT2

FB2

63.4k

OFF ON OFF ON

Conversion Efficiency

LED CURRENT (mA)

EFFICIENCY (%)

3466 F01b

= 3.6V

8/8 LEDs

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (20 pages)

PAGE 1
LT3466 Dual Full Function White LED Step-Up Converter with Built-In Schottky Diodes U FEATURES DESCRIPTIO ■ LT®3466 is a dual full function step-up DC/DC converter specifically designed to drive up to 20 White LEDs (10 in series per converter) with a constant current. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors and expensive factory calibration.
PAGE 2
LT3466 W W W AXI U U ABSOLUTE RATI GS (Note 1) Input Voltage (VIN) ................................................... 24V SW1, SW2 Voltages ................................................ 44V VOUT1, VOUT2 Voltages ............................................. 44V CTRL1, CTRL2 Voltages ........................................... 24V FB1, FB2, RT Voltages ................................................ 2V Operating Temperature Range (Note 2) ... –40°C to 85°C Maximum Junction Temperature ..........
PAGE 3
LT3466 ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, VCTRL1 = 3V, VCTRL2 = 3V, unless otherwise specified. PARAMETER CONDITIONS MIN TYP Converter 1 Current Limit (Note 5) ● 320 400 mA Converter 2 Current Limit (Note 5) ● 320 400 mA Converter 1 VCESAT ISW1 = 300mA 360 mV Converter 2 VCESAT ISW2 = 300mA 360 mV Switch 1 Leakage Current VSW1 = 10V 0.
PAGE 4
LT3466 U W TYPICAL PERFOR A CE CHARACTERISTICS VFB vs VCTRL (Temperature Variation) VFB vs VCTRL 250 200 150 100 200 150 100 0 1 0.5 1.5 CONTROL VOLTAGE (V) 0 2 350 150 200 150 50 0 0 100 150 200 250 300 350 400 SWITCH CURRENT (mA) 20 0 60 40 DUTY CYCLE (%) 80 VOUT1 39.0 2 4 6 8 10 12 14 16 18 20 22 24 VIN (V) 3466 G07 TA = 25°C 70 TA = 100°C 60 50 40 30 20 0 100 2 4 6 Input Current with Output 1 and Output 2 Open Circuit 25 TA = 25°C RT = 63.4k VIN = 3.6V RT = 63.
PAGE 5
LT3466 U W TYPICAL PERFOR A CE CHARACTERISTICS Oscillator Frequency vs VIN RT vs Oscillator Frequency 1200 OSCILLATOR FREQUENCY (kHz) RT (kΩ) 1000 100 10 200 RT = 48.7k 1100 1000 900 800 600 1000 1400 1800 OSCILLATOR FREQUENCY (kHz) 4 2 6 8 10 12 14 16 18 20 22 24 VIN (V) 3466 G10 3466 G11 Oscillator Frequency vs Temperature Quiescent Current (CTRL1 = CTRL2 = 3V) 6 2500 2250 5 RT = 20.5k 2000 QUIESCENT CURRENT (mA) OSCILLATOR FREQUENCY (kHz) TA = 25°C VIN = 3.
PAGE 6
LT3466 U U U PI FU CTIO S (DD/TSSOP) VOUT1 (Pin 1/Pin 3): Output of Converter 1. This pin is connected to the cathode of the internal Schottky diode. Connect an output capacitor from this pin to ground. RT (Pin 8/Pin 12): Timing Resistor to Program the Switching Frequency. The switching frequency can be programmed from 200KHz to 2MHz. SW1 (Pin 2/Pin 4): Switch Pin for Converter 1. Connect the inductor at this pin. CTRL1 (Pin 9/Pin 14): Dimming and Shutdown Pin for Converter 1.
PAGE 7
C2 RFB1 FB1 PWM LOGIC PWM COMP A2 RSNS1 DRIVER CONVERTER 1 OSC OVERVOLT DETECTION Q1 SW1 – + A3 EA PIN NUMBERS CORRESPOND TO THE 10-PIN DFN PACKAGE 10 1 2 – + VOUT1 L1 A1 Σ 20k + + – C1 RT 9 VIN START-UP CONTROL REF 1.25V CTRL1 SHDN OSC 3 7 CTRL2 80k 0.2V Figure 2. LT3466 Block Diagram 80k 0.
PAGE 8
LT3466 U OPERATIO Main Control Loop The LT3466 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. It incorporates two identical, but fully independent PWM converters. Operation can be best understood by referring to the Block Diagram in Figure 2. The oscillator, start-up bias and the bandgap reference are shared between the two converters. The control circuitry, power switch, Schottky diode etc., are all identical for both the converters.
PAGE 9
LT3466 U OPERATIO However, the other converter will continue functioning properly. The photo in Figure 4b shows circuit operation with converter 1 output open-circuit and converter 2 driving eight LEDs at 20mA. Converter 1 starts switching at a lower peak inductor current and begins skipping pulses, thereby reducing its input current. Soft-Start The LT3466 has a separate internal soft-start circuitry for each converter. Soft-start helps to limit the inrush current during start-up.
PAGE 10
LT3466 U W U U APPLICATIO S I FOR ATIO DUTY CYCLE The duty cycle for a step-up converter is given by: D= VOUT + VD – VIN VOUT + VD – VCESAT current that flows into the timing resistor is used to charge and discharge an internal oscillator capacitor. A graph for selecting the value of RT for a given operating frequency is shown in Figure 6.
PAGE 11
LT3466 U W U U APPLICATIO S I FOR ATIO INDUCTOR SELECTION CAPACITOR SELECTION The choice of the inductor will depend on the selection of the switching frequency of the LT3466. The switching frequency can be programmed from 200kHz to 2MHz. Higher switching frequency allows the use of smaller inductors albeit at the cost of increased switching losses. The small size of ceramic capacitors make them ideal for LT3466 applications.
PAGE 12
LT3466 U W U U APPLICATIO S I FOR ATIO Table 3. Inrush Peak Current Using a DC Voltage VIN (V) L (µH) COUT (µF) IP (A) 5 15 0.47 0.78 5 33 1.00 0.77 5 47 2.2 0.95 5 68 1.00 0.53 9 47 0.47 0.84 12 33 0.22 0.93 Typically peak inrush current will be less than the value calculated above. This is due to the fact that the DC resistance in the inductor provides some damping resulting in a lower peak inrush current.
PAGE 13
LT3466 U W U U APPLICATIO S I FOR ATIO Figure 9 shows four LEDs being powered off two AA cells. The battery is connected to the inductors and the chip is powered off 3.3V logic supply voltage. 3.3V 2 AA CELLS 1.8V to 3V 0.1µF 1µF L2 15µH L1 15µH SW1 VIN SW2 VOUT2 VOUT1 1µF 1µF LT3466 FB1 CTRL1 FB2 RT CTRL2 10Ω 10Ω OFF ON 63.4k 1% OFF ON 3466 F09 BOARD LAYOUT CONSIDERATION As with all switching regulators, careful attention must be paid to the PCB board layout and component placement.
PAGE 14
LT3466 U TYPICAL APPLICATIO S Li-Ion to 2/4 White LEDs Conversion Efficiency 3V TO 5V 85 CIN 1µF VIN = 3.6V 2/4 LEDs 80 L2 15µH SW1 VIN SW2 VOUT2 VOUT1 COUT1 1µF COUT2 0.47µF LT3466 FB1 RFB1 10Ω EFFICIENCY (%) 75 L1 15µH RT OFF ON 55 RFB2 10Ω CTRL2 OFF ON 38.
PAGE 15
LT3466 U TYPICAL APPLICATIO S Li-Ion to 6/6 White LEDs Conversion Efficiency 3V TO 5V 85 VIN = 3.6V 6/6 LEDs 80 CIN 1µF L2 33µH SW1 VIN SW2 VOUT1 COUT1 1µF VOUT2 LT3466 FB1 COUT2 1µF RT OFF ON 65 55 CTRL2 50 0 RFB2 10Ω OFF ON 63.
PAGE 16
LT3466 U TYPICAL APPLICATIO S Li-Ion to 8/8 White LEDs Conversion Efficiency 3V TO 5V 85 CIN 1µF VIN = 3.6V 8/8 LEDs 80 SW1 COUT1 2.2µF EFFICIENCY (%) 75 L2 47µH L1 47µH VIN SW2 VOUT2 VOUT1 LT3466 RT 65 60 FB2 55 CTRL2 50 FB1 CTRL1 COUT2 2.2µF 70 5 0 OFF ON OFF ON 63.4k 1% RFB1 10Ω 3466 TA05a Conversion Efficiency 3V TO 5V 90 CIN 1µF EFFICIENCY (%) COUT1 1µF SW2 VOUT2 VOUT1 VIN = 3.
PAGE 17
LT3466 U TYPICAL APPLICATIO S Li-Ion to 10/10 White LEDs Conversion Efficiency 3V TO 5V 90 CIN 1µF L2 68µH VIN SW2 VOUT2 VOUT1 COUT1 1µF EFFICIENCY (%) 85 L1 68µH SW1 VIN = 3.6V 10/10 LEDs COUT2 1µF LT3466 80 75 70 65 FB1 CTRL1 OFF ON RFB1 16.5Ω FB2 RT 60 CTRL2 RFB2 16.5Ω 3466 TA07a Conversion Efficiency 3.3V 75 CIN1 0.1µF VIN SW2 VOUT2 VOUT1 COUT1 1µF COUT2 1µF LT3466 FB1 RFB1 10Ω CTRL1 OFF ON FB2 RT CTRL2 63.
PAGE 18
LT3466 U TYPICAL APPLICATIO S 2 Li-Ion Cells to 10/10 White LEDs Conversion Efficiency 90 6V TO 9V L2 47µH SW1 VIN VOUT2 COUT2 0.47µF LT3466 FB1 CTRL1 OFF ON RFB1 10Ω SW2 VOUT1 COUT1 0.47µF 80 EFFICIENCY (%) L1 47µH 70 65 55 50 CTRL2 63.4k 1% 75 60 FB2 RT VIN = 7V 10/10 LEDs 85 CIN 1µF 0 10 5 RFB2 10Ω 3466 TA09a Conversion Efficiency 2 Li-Ion Cells to 16/16 White LEDs 6V TO 9V 90 D3 80 VLED1 VLED2 D2 D4 L1 L2 47µH 47µH C1 0.1µF 16 LEDs SW1 VIN C4 0.
PAGE 19
LT3466 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 6 0.38 ± 0.10 10 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) PACKAGE OUTLINE (DD10) DFN 1103 5 0.25 ± 0.05 1 0.75 ±0.05 0.200 REF 0.50 BSC 2.38 ±0.05 (2 SIDES) 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1.
PAGE 20
LT3466 U TYPICAL APPLICATIO Conversion Efficiency 12V to 25/25 White LEDs CAR BATTERY 12V (TYP) 9V TO 18V 85 D9 C4 0.1µF D7 25 LEDs C5 0.1µF L1 33µH C2 0.1µF L2 33µH D1 C7 0.1µF D2 VLED2 3.3V C8 0.1µF C3 0.1µF C9 0.1µF D3 CIN D4 D8 SW1 VIN C6 0.22µF SW2 VOUT2 VOUT1 LT3466 C10 0.1µF 25 LEDs RT 70 65 60 55 C11 0.