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LT3466-1

34661f

White LED Driver and Boost

Converter in 3mm × 3mm

DFN Package

Figure 1. Li-Ion Powered Driver for 6 White LEDs and OLED Display

■

Drives Up to 10 White LEDs from a 3.6V Supply

■

Two Independent Step-Up DC/DC Converters

■

Independent Dimming and Shutdown Control

of the Outputs

■

±1.5% Output Voltage Accuracy (Boost Converter)

■

±4% LED Current Programming Accuracy

■

Internal Schottky Diodes

■

Internal Soft-Start Eliminates Inrush Current

■

Output Overvoltage Protection (39.5V Max V

OUT

)

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Fixed Frequency Operation Up to 2MHz

■

83% Efficiency Driving 8 White LEDs at 15mA

from a 3.6V Supply

■

Wide Input Voltage Range: 2.7V to 24V

■

Tiny (3mm × 3mm) 10-Lead DFN Package

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White LED and OLED Displays

■

Digital Cameras, Sub-Notebook PCs

■

PDAs, Handheld Computers

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TFT - LCD Bias Supply

■

Automotive

3466-1 is a dual switching regulator that combines a

white LED driver and a boost converter in a low profile,

small footprint (3mm × 3mm × 0.75mm) DFN package.

The LED driver can be configured to drive up to 10 White

LEDs in series and the boost converter can be used for

generating the LCD bias voltages or driving a secondary

OLED display. 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 LT3466-1 provides independent dimming and shut-

down control of the two converters. The operating fre-

quency can be set with an external resistor over a 200kHz

to 2MHz range. The white LED driver features a low 200mV

reference, thereby minimizing power loss in the current

setting resistor for better efficiency. The boost converter

achieves ±1.5% output voltage accuracy by the use of a

precision 0.8V reference. Protection features include out-

put overvoltage protection and internal soft-start. Wide

input supply range allows operation from 2.7V to 24V.

3V TO 5V

16V

30mA

33µH

1µF

1µF1µF

6 LEDs

33µH

SHUTDOWN

AND DIMMING

CONTROL 2

SHUTDOWN

AND DIMMING

CONTROL 1

10Ω

24.9k

475k

34661 F01a

63.4k

CTRL1 GND CTRL2

SW1 SW2V

LT3466-1

OUT1

FB1

OUT2

FB2

Conversion Efficiency

OUTPUT CURRENT (mA)

EFFICIENCY (%)

302520

34661 F01b

51015

BOOST CONVERTER

LED DRIVER

= 3.6V

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

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

All other trademarks are the property of their respective owners.

Summary of content (20 pages)

PAGE 1
LT3466-1 White LED Driver and Boost Converter in 3mm × 3mm DFN Package U FEATURES DESCRIPTIO ■ LT®3466-1 is a dual switching regulator that combines a white LED driver and a boost converter in a low profile, small footprint (3mm × 3mm × 0.75mm) DFN package. The LED driver can be configured to drive up to 10 White LEDs in series and the boost converter can be used for generating the LCD bias voltages or driving a secondary OLED display.
PAGE 2
LT3466-1 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) Input Voltage (VIN) ................................................... 24V SW1, SW2 Voltages ................................................ 44V VOUT1, VOUT2 Voltages ............................................. 44V CTRL1, CTRL2 Voltages ........................................... 24V FB1, FB2 Voltages ...................................................... 2V Operating Temperature Range (Note 2) ...
PAGE 3
LT3466-1 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 MAX UNITS VOUT1 Overvoltage Threshold 39.5 V VOUT2 Overvoltage Threshold 39.5 V Schottky 1 Forward Drop ISCHOTTKY1 = 300mA 0.85 V Schottky 2 Forward Drop ISCHOTTKY2 = 300mA 0.
PAGE 4
LT3466-1 U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise specified 500 7 TA = –50°C 450 UVLO TA = 85°C 350 300 250 200 150 100 5 4 3 2 1 50 80 0 100 4 8 12 VIN (V) 16 Open-Circuit Output Clamp Voltage OUTPUT CLAMP VOLTAGE (V) OUTPUT CLAMP VOLTAGE (V) 42 40.50 40.00 VOUT2 39.50 VOUT1 39.00 38.50 38.
PAGE 5
LT3466-1 U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise specified Oscillator Frequency vs Temperature 150 VIN = 3.6V RT = 48.7k VIN = 3.
PAGE 6
LT3466-1 U U U PI FU CTIO S VOUT1 (Pin 1): 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. SW1 (Pin 2): Switch Pin for Converter 1. Connect the inductor at this pin. VIN (Pin 3): Input Supply Pin. Must be locally bypassed with a 1µF, X5R or X7R type ceramic capacitor. SW2 (Pin 4): Switch Pin for Converter 2. Connect the inductor at this pin. VOUT2 (Pin 5): Output of Converter 2.
PAGE 7
C2 RFB1 10 1 FB1 PWM LOGIC PWM COMP A2 RSNS1 DRIVER CONVERTER 1 OSC OVERVOLT DETECTION SW1 Q1 2 – + VOUT1 L1 – + A3 EA A1 Σ 20k + + – C1 RT 9 VIN START-UP CONTROL REF 1.25V CTRL1 SHDN OSC 3 7 CTRL2 0.8V Figure 2. Block Diagram 80k 0.
PAGE 8
LT3466-1 U OPERATIO Main Control Loop Minimum Output Current The LT3466-1 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. It incorporates two similar, 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 similar for both converters.
PAGE 9
LT3466-1 U OPERATIO In the event one of the converters has an output open-circuit, its output voltage will be clamped at 39.5V. 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 the OLED display. Converter 1 starts switching at a lower inductor current and begins skipping pulses, thereby reducing its input current. Converter 2 continues functioning properly.
PAGE 10
LT3466-1 U W U U APPLICATIO S I FOR ATIO DUTY CYCLE OPERATING FREQUENCY SELECTION The duty cycle for a step-up converter is given by: The choice of operating frequency is determined by several factors. There is a tradeoff between efficiency and component size. Higher switching frequency allows the use of smaller inductors albeit at the cost of increased switching losses and decreased efficiency.
PAGE 11
LT3466-1 U W U U APPLICATIO S I FOR ATIO The inductor current ripple (∆IL), neglecting the drop across the Schottky diode and the switch, is given by : ∆IL = ( VIN(MIN) • VOUT(MAX) – VIN(MIN) ) VOUT(MAX) • f • L where: Z5U. A 1µF input capacitor is sufficient for most applications. Always use a capacitor with sufficient voltage rating. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information on their entire selection of ceramic parts.
PAGE 12
LT3466-1 U W U U APPLICATIO S I FOR ATIO 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. SETTING THE LED CURRENT The current in the LED string can be set by the choice of the resistor RFB1 (Figure 1). The feedback reference is 200mV. In order to have accurate LED current, precision resistors are preferred (1% is recommended).
PAGE 13
LT3466-1 U W U U APPLICATIO S I FOR ATIO Figure 9 shows the feedback voltage variation versus the control voltage. As seen in Figure 9, the linearity of the graph allows the feedback voltage to be set accurately via the control voltage. 3V TO 5V CIN 1µF L1 33µH The boost converter output voltage (VOUT2) is given by: VOUT 2 L2 33µH SW1 ⎛ R1⎞ = VFB2 ⎜ 1+ ⎟ ⎝ R2⎠ Thus a linear change in the feedback (FB2) voltage results in a linear change in the boost output voltage (VOUT2).
PAGE 14
LT3466-1 U W U U APPLICATIO S I FOR ATIO The VCE(SAT) and VBE(SAT) values for the transistor Q1 can be obtained from the Philips BC807 data sheet: RBASE = 16 V – 5V + 0 . 1 – 0 . 9 0 . 75mA ground plane and not shared with any other component, except the RT resistor, ensuring a clean, noise-free connection. Recommended component placement is shown in the Figure 11. RBASE = 13.
PAGE 15
LT3466-1 U TYPICAL APPLICATIO S Li-Ion Powered 4 White LEDs Driver and 12V Boost Converter 3V TO 5V Efficiency vs Load Current CIN 1µF 4 LEDs L2 15µH SW1 VIN SW2 VOUT2 VOUT1 COUT1 0.47µF R1 909k COUT2 1µF LT3466-1 FB1 RFB1 10Ω FB2 RT CTRL1 OFF ON R2 64.9k CTRL2 38.
PAGE 16
LT3466-1 U TYPICAL APPLICATIO S Li-Ion Powered Driver for 6 White LEDs and OLED with Output Disconnect 3V TO 5V 14k CIN 1µF L1 33µH Q1 L2 33µH COUT3 0.47µF 6 LEDs SW1 COUT1 1µF VIN VOUT2 COUT2 0.47µF LT3466-1 CTRL1 OFF ON R1 475k SW2 VOUT1 FB1 RFB1 10Ω 16V 30mA FB2 RT R2 24.9k CTRL2 63.
PAGE 17
LT3466-1 U TYPICAL APPLICATIO S Li-Ion Powered Driver for 6 White LEDs and OLED with Output Disconnect 3V TO 5V CIN 1µF L1 33µH 6 LEDs L2 33µH SW1 VIN COUT3 0.47µF R1 475k SW2 VOUT1 COUT1 1µF VOUT2 COUT2 0.47µF LT3466-1 FB1 RFB1 10Ω CTRL1 OFF ON 16V 30mA Q1 FB2 RT R2 24.9k CTRL2 63.
PAGE 18
LT3466-1 U TYPICAL APPLICATIO S Li-Ion to 10 White LEDs and LCD Bias (±8V) with Output Disconnect 3V TO 5V CIN 1µF L1 68µH C1 0.1µF –8V 10mA L2 33µH 10 LEDs SW1 COUT1 1µF D1 VIN COUT2 1µF C2 0.1µF SW2 D2 VOUT2 VOUT1 8V 10mA LT3466-1 909k FB1 RFB1 16.
PAGE 19
LT3466-1 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 6 3.00 ±0.10 (4 SIDES) 0.38 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD10) DFN 1103 5 0.200 REF 1 0.75 ±0.05 0.00 – 0.05 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1.
PAGE 20
LT3466-1 U TYPICAL APPLICATIO Li-Ion to 8 White LEDs and ±15V TFT LCD Bias Supply 3V TO 5V SW1 COUT1 1µF VIN 15V 10mA LT3466-1 OFF ON 86 475k COUT2 1µF FB2 26.7k CTRL2 63.4k VIN = 3.6V 8 LEDs +15V/10mA –15V/10mA 84 COUT3 1µF VOUT2 FB1 RFB1 13.3Ω D1 SW2 VOUT1 CTRL1 RT Conversion Efficiency –15V 10mA L2 33µH L1 33µH 8 LEDs C1 0.