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. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors and expensive factory calibration. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 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 VOUT) 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 U APPLICATIO S ■ ■ ■ ■ White LED and OLED Displays Digital Cameras, Sub-Notebook PCs PDAs, Handheld Computers TFT - LCD Bias Supply Automotive , LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. U ■ The LT3466-1 provides independent dimming and shutdown control of the two converters. The operating frequency 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 output overvoltage protection and internal soft-start. Wide input supply range allows operation from 2.7V to 24V. TYPICAL APPLICATIO 3V TO 5V Conversion Efficiency 33µH 33µH 1µF 90 VIN = 3.6V 85 6 LEDs VOUT1 VIN LT3466-1 80 VOUT2 1µF 1µF FB1 FB2 RT GND CTRL1 10Ω LED DRIVER SW2 SHUTDOWN AND DIMMING CONTROL 1 63.4k 16V 30mA 475k CTRL2 SHUTDOWN AND DIMMING CONTROL 2 EFFICIENCY (%) SW1 BOOST CONVERTER 75 70 65 60 55 24.9k 34661 F01a 50 0 5 10 15 20 25 30 OUTPUT CURRENT (mA) 34661 F01b Figure 1. Li-Ion Powered Driver for 6 White LEDs and OLED Display 34661f 1 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) ... –40°C to 85°C Storage Temperature Range .................. –65°C to 125°C Junction Temperature .......................................... 125°C ORDER PART NUMBER TOP VIEW 10 FB1 VOUT1 1 SW1 2 VIN 3 SW2 4 8 RT 7 CTRL2 VOUT2 5 6 FB2 9 CTRL1 11 LT3466EDD-1 DD PART MARKING DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN LBRX TJMAX = 125°C, θJA = 43°C/W, θJC = 3°C/W EXPOSED PAD (PIN 11) IS GND MUST BE SOLDERED TO PCB Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. 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 Minimum Operating Voltage TYP MAX 2.7 UNITS V Maximum Operating Voltage 22 V FB1 Voltage ● 192 200 208 mV FB2 Voltage ● 788 800 812 mV FB1 Pin Bias Current VFB1 = 0.2V (Note 3) 10 50 nA FB2 Pin Bias Current VFB2 = 0.8V (Note 3) 10 50 nA Quiescent Current VFB1 = VFB2 = 1V CTRL1 = CTRL2 = 0V 5 16 7.5 25 mA µA Switching Frequency RT = 48.7k 0.75 1.25 MHz Oscillator Frequency Range (Note 4) 200 2000 kHz Nominal RT Pin Voltage RT = 48.7k Maximum Duty Cycle RT = 48.7k RT = 20.5k RT = 267k Converter 1 Current Limit Converter 2 Current Limit 1 0.54 V ● 90 96 92 99 % % % ● 310 400 mA ● 310 400 mA 320 mV Converter 1 VCESAT ISW1 = 300mA Converter 2 VCESAT ISW2 = 300mA 320 Switch 1 Leakage Current VSW1 = 10V 0.01 5 µA Switch 2 Leakage Current VSW2 = 10V 0.01 5 µA CTRL1 Voltage for Full LED Current ● CTRL2 Voltage for Full Feedback Voltage ● CTRL1 or CTRL2 Voltage to Turn On the IC mV 1.8 V 1 V 150 mV CTRL1 and CTRL2 Voltages to Shut Down Chip CTRL1 Pin Bias Current VCTRL1 = 1V ● CTRL2 Pin Bias Current VCTRL2 = 1V (Note 3) ● 6 70 mV 9 12.5 µA 10 120 nA 34661f 2 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 0.85 V Schottky 1 Reverse Leakage VOUT1 = 20V Schottky 2 Reverse Leakage VOUT2 = 20V 5 µA 5 µA Soft-Start Time (Switcher 1) 600 µs Soft-Start Time (Switcher 2) 600 µs Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3466-1E is guaranteed to meet specified performance from 0°C to 70°C. Specifications over the –40°C to 85°C operating range are assured by design, characterization and correlation with statistical process controls. Note 3: Current flows out of the pin. Note 4: Guaranteed by design and test correlation, not production tested. U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise specified Switching Waveforms (LED Driver) Switching Waveforms (Boost Converter) VOUT1 100mV/DIV (AC-COUPLED) VOUT2 100mV/DIV (AC-COUPLED) VSW1 20V/DIV VSW2 20V/DIV IL2 100mA/DIV IL1 100mA/DIV VIN = 3.6V 0.5µs/DIV 6 LEDs AT 20mA CIRCUIT OF FIGURE 1 VIN = 3.6V 0.5µs/DIV VOUT2 = 16V/30mA CIRCUIT OF FIGURE 1 34661 G01 VFB1 vs VCTRL1 250 34661 G02 VFB2 vs VCTRL2 900 VIN = 3.6V 6 LEDs VIN = 3.6V 800 VOUT2 = 16V 200 700 VFB2 (mV) VFB1 (mV) 600 150 100 500 400 300 200 50 100 0 0 0.5 1 1.5 2 VCTRL1 (V) 0 0 0.5 1 1.5 2 VCTRL2 (V) 34661 G03 34661 G16 34661f 3 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 38.00 4 6 8 10 12 14 16 18 20 22 24 VIN (V) 4 6 8 10 12 14 16 18 20 22 24 VIN (V) 34661 G06 Input Current with Output 1 and Output 2 Open Circuit 20 41 40 VOUT1 39 38 37 –50 RT = 63.4k 16 VOUT2 12 8 4 –25 50 25 0 75 TEMPERATURE (°C) 100 125 0 2 4 6 8 10 12 14 16 18 20 22 24 VIN (V) 34661 G08 34661 G09 Oscillator Frequency vs VIN RT vs Oscillator Frequency 1000 1100 OSCILLATOR FREQUENCY (kHz) RT (kΩ) 20 2 RT = 63.4k 34661 G07 100 10 200 TA = 100°C 30 Open-Circuit Output Clamp Voltage RT = 63.4k 2 40 34661 G04 34661 G05 41.00 TA = 25°C 0 24 20 INPUT CURRENT (mA) 60 40 DUTY CYCLE (%) 50 10 0 20 0 TA = –50°C 60 SHUTDOWN CURRENT (µA) QUIESCENT CURRENT (mA) CURRENT LIMIT (mA) 70 TA = 25°C 6 400 0 Shutdown Current (CTRL1 = CTRL2 = 0V) Quiescent Current (CTRL1 = CTRL2 = 3V) Switch Current Limit vs Duty Cycle 600 1000 1400 1800 OSCILLATOR FREQUENCY (kHz) 34661 G10 RT = 48.7k 1000 900 800 2 4 6 8 10 12 14 16 18 20 22 24 VIN (V) 34661 G11 34661f 4 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 = 3.6V 125 CTRL1 CTRL VOLTAGE (mV) OSCILLATOR FREQUENCY (kHz) 1100 CTRL Voltages to Shut Down the IC 1000 900 100 CTRL2 75 50 25 800 –50 –25 0 25 50 TEMPERATURE (°C) 75 0 –50 100 –25 75 0 25 50 TEMPERATURE (°C) 34661 G12 34661 G13 Schottky Forward Voltage Drop Schottky Leakage Current 8 SCHOTTKY LEAKAGE CURRENT (µA) SCHOTTKY FORWARD CURRENT (mA) 400 350 300 250 200 150 100 50 0 200 800 600 SCHOTTKY FORWARD DROP (mV) 0 400 6 4 VR = 36V VR = 20V 2 0 –50 1000 –25 75 0 25 50 TEMPERATURE (°C) FB2 Pin Load Regulation FB2 Pin Voltage vs Temperature 0 VIN = 3V VOUT2 = 16V/30mA VIN = 3V VOUT2 = 16V –0.20 ∆VOUT2/VOUT2 (%) FB2 VOLTAGE (V) 0.805 0.800 0.795 0.790 –0.40 –0.60 –0.80 0.785 0.780 –50 100 34661 G015 34661 G14 0.810 100 –1.00 –25 75 0 25 50 TEMPERATURE (°C) 100 125 34661 G17 0 10 20 LOAD CURRENT (mA) 30 34661 G18 34661f 5 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. This pin is connected to the cathode of the internal Schottky diode. Connect an output capacitor from this pin to ground. FB2 (Pin 6): Feedback Pin for Converter 2. The nominal voltage at this pin is 800mV. Connect the resistor divider to this pin. The feedback voltage can be programmed as: VFB2 ≈ VCTRL2, when VCTRL2 < 0.8V VFB2 = 0.8V, when VCTRL2 > 1V CTRL2 (Pin 7): Dimming and Shutdown Pin for Converter 2. As the pin voltage is ramped from 0V to 1V, the FB2 pin voltage tracks the CTRL2 voltage and ramps up to 0.8V. Any voltage above 1V does not affect the feedback voltage. Do not leave the pin floating. It must be connected to ground to disable converter 2. RT (Pin 8): Timing Resistor to Program the Switching Frequency. The switching frequency can be programmed from 200KHz to 2MHz. CTRL1 (Pin 9): Dimming and Shutdown Pin for Converter 1. Connect this pin to ground to disable the converter. As the pin voltage is ramped from 0V to 1.8V, the LED current ramps from 0 to ILED1 (= 200mV/RFB1). Any voltage above 1.8V does not affect the LED current. FB1 (Pin 10): Feedback Pin for Converter 1. The nominal voltage at this pin is 200mV. Connect cathode of the lowest LED and the feedback resistor at this pin. The LED current can be programmed by : ILED1 ≈ (VCTRL1/5 • RFB1), when VCTRL1 < 1V ILED1 ≈ (200mV/RFB1), when VCTRL1 > 1.8V Exposed Pad (Pin 11): The Exposed Pad must be soldered to the PCB system ground. 34661f 6 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 0.2V RAMP GEN OSC 8 RT + + – Σ A1 EA A3 11 EXPOSED PAD – + Q2 4 A2 OSC PWM LOGIC VOUT2 FB2 OVERVOLT DETECTION CONVERTER 2 PWM COMP DRIVER RSNS2 SW2 L2 – + VIN 6 5 34661 F02 R2 R1 C3 LT3466-1 BLOCK DIAGRA 34661f 7 W 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. The LT3466-1 can drive a 6-LED string at 3mA LED current without pulse skipping. As current is further reduced, the device may begin skipping pulses. This will result in some low frequency ripple, although the LED current remains regulated on an average basis down to zero. The photo in Figure 3 shows circuit operation with 6 white LEDs at 3mA current driven from 3.6V supply. Peak inductor current is less than 50mA and the regulator operates in discontinuous mode implying that the inductor current reached zero during the discharge phase. After the inductor current reaches zero, the switch pin exhibits ringing due to the LC tank circuit formed by the inductor in combination with switch and diode capacitance. This ringing is not harmful; far less spectral energy is contained in the ringing than in the switch transitions. The ringing can be damped by application of a 300Ω resistor across the inductors, although this will degrade efficiency. At power-up, the output voltages VOUT1 and VOUT2 are charged up to VIN (input supply voltage) via their respective inductor and the internal Schottky diode. If either CTRL1 and CTRL2 or both are pulled high, the bandgap reference, start-up bias and the oscillator are turned on. Working of the main control loop can be understood by following the operation of converter 1. At the start of each oscillator cycle, the power switch Q1 is turned on. A voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of A2, the PWM logic turns off the power switch. The level at the negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and the 200mV reference voltage. In this manner, the error amplifier A1 regulates the voltage at the FB1 pin to 200mV. The output of the error amplifier A1 sets the correct peak current level in inductor L1 to keep the output in regulation. The CTRL1 pin voltage is used to adjust the feedback voltage. The working of converter 2 is similar to converter 1 with the exception that the feedback 2 reference voltage is 800mV. The error amplifier A1 in converter 2 regulates the voltage at the FB2 pin to 800mV. If only one of the converters is turned on, the other converter will stay off and its output will remain charged up to VIN (input supply voltage). The LT3466-1 enters into shutdown, when both CTRL1 and CTRL2 are pulled lower than 70mV. The CTRL1 and CTRL2 pins perform independent dimming and shutdown control for the two converters. VOUT1 20mV/DIV (AC-COUPLED) VSW1 20V/DIV IL1 50mA/DIV 0.5µs/DIV VIN = 3.6V ILED1 = 3mA CIRCUIT OF FIGURE 1 34661 F03 Figure 3. Switching Waveforms Overvoltage Protection The LT3466-1 has internal overvoltage protection for both converters. In the event the white LEDs are disconnected from the circuit or fail open, the converter 1 output voltage is clamped at 39.5V (typ). Figure 4(a) shows the transient response of the circuit in Figure 1 with LED1 disconnected. With the white LEDs disconnected, the converter 1 starts switching at the peak current limit. The output of converter 1 starts ramping up and finally gets clamped at 39.5V (typ). The converter 1 will then switch at low inductor current to regulate the output voltage. Output voltage and input current during output open circuit are shown in the Typical Performance Characteristics graphs. 34661f 8 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. Soft-Start The LT3466-1 has a separate internal soft-start circuitry for each converter. Soft-start helps to limit the inrush current during start-up. Soft-start is achieved by clamping the output of the error amplifier during the soft-start period. This limits the peak inductor current and ramps up the output voltage in a controlled manner. The converter enters into soft-start mode whenever the respective CTRL pin is pulled from low to high. Figure 5 shows the start-up waveforms with converter 1 driving six LEDs at 20mA. The filtered input current, as shown in Figure 5, is well controlled. The soft-start circuitry is less effective when driving a higher number of LEDs. VOUT1 10V/DIV IL1 200mA/DIV Undervoltage Lockout 200µs/DIV 34661 F04a LED1 DISCONNECTED AT THIS POINT VIN = 3.3V CIRCUIT OF FIGURE 1 Figure 4a. Transient Response of Switcher 1 with LED1 Disconnected from the Output VSW1 50V/DIV The LT3466-1 has an undervoltage lockout circuit which shuts down both converters when the input voltage drops below 2.1V (typ). This prevents the converter from switching in an erratic mode when powered from low supply voltages. IIN 200mA/DIV IL1 100mA/DIV VOUT1 20V/DIV VSW2 50V/DIV VFB1 200mV/DIV IL2 100mA/DIV CTRL1 5V/DIV VIN = 3.6V 1µs/DIV CIRCUIT OF FIGURE 1 34661 F04b Figure 4b. Output 1 Open-Circuit Waveforms VIN = 3.6V 200µs/DIV 6 LEDs, 20mA CIRCUIT OF FIGURE 1 34661 F05 Figure 5. Start-Up Waveforms 34661f 9 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. D= VOUT + VD – VIN VOUT + VD – VCESAT where: VOUT = Output voltage VD = Schottky forward voltage drop VCESAT = Saturation voltage of the switch VIN = Input battery voltage Another consideration is the maximum duty cycle achievable. In certain applications, the converter needs to operate at the maximum duty cycle in order to light up the maximum number of LEDs. The LT3466-1 has a fixed oscillator off-time and a variable on-time. As a result, the maximum duty cycle increases as the switching frequency is decreased. The maximum duty cycle achievable for LT3466-1 is 96% (typ) when running at 1MHz switching frequency. It increases to 99% (typ) when run at 200kHz and drops to 92% (typ) at 2MHz. Always ensure that the converter is not duty-cycle limited when powering the LEDs or OLED at a given switching frequency. The circuit of Figure 1 is operated with different values of timing resistor (RT). RT is chosen so as to run the converters at 800kHz (RT = 63.4k), 1.25MHz (RT = 38.3k) and 2MHz (RT = 20.5k). The efficiency comparison for different RT values is shown in Figure 7. SETTING THE SWITCHING FREQUENCY INDUCTOR SELECTION The LT3466-1 uses a constant frequency architecture that can be programmed over a 200KHz to 2MHz range with a single external timing resistor from the RT pin to ground. The nominal voltage on the RT pin is 0.54V, and the 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 the Figure 6. The choice of the inductor will depend on the selection of switching frequency of LT3466-1. 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. 90 1000 CIRCUIT OF FIGURE 1 VIN = 3.6V 6 LEDs EFFICIENCY (%) RT (kΩ) 80 100 RT = 63.4k RT = 20.5k 70 RT = 38.3k 60 50 10 200 600 1000 1400 1800 OSCILLATOR FREQUENCY (kHz) 34661 F06 Figure 6. Timing Resistor (RT) Value 40 0 5 10 15 20 LED CURRENT (mA) 34661 F07 Figure 7. Efficiency Comparison for Different RT Resistors 34661f 10 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. Table 2. Ceramic Capacitor Manufacturers L = Inductor Taiyo Yuden (408) 573-4150 www.t-yuden.com f = Operating frequency AVX VIN(MIN) = Minimum input voltage (803) 448-9411 www.avxcorp.com Murata (714) 852-2001 www.murata.com VOUT(MAX) = Maximum output voltage The ∆IL is typically set to 20% to 40% of the maximum inductor current. The inductor should have a saturation current rating greater than the peak inductor current required for the application. Also, ensure that the inductor has a low DCR (copper wire resistance) to minimize I2R power losses. Recommended inductor values range from 10µH to 68µH. Several inductors that work well with the LT3466-1 are listed in Table 1. Consult each manufacturer for more detailed information and for their entire selection of related parts. Table 1. Recommended Inductors L (µH) MAX DCR (Ω) CURRENT RATING (mA) LQH32CN100 LQH32CN150 LQH43CN330 10 15 33 0.44 0.58 1.00 300 300 310 Murata (814) 237-1431 www.murata.com ELL6RH330M ELL6SH680M 33 68 0.38 0.52 600 500 Panasonic (714) 373-7939 www.panasonic.com A914BYW330M A914BYW470M A920CY680M 33 47 68 0.45 0.73 0.40 440 360 400 Toko www.toko.com CDRH2D18150NC CDRH4D18-330 CDRH5D18-680 15 33 68 0.22 0.51 0.84 0.35A 0.31A 0.43A PART VENDOR Sumida (847) 956-0666 www.sumida.com CAPACITOR SELECTION The small size of ceramic capacitors make them ideal for LT3466-1 applications. Use only X5R and X7R types because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or INRUSH CURRENT The LT3466-1 has built-in Schottky diodes. When supply voltage is applied to the VIN pin, an inrush current flows through the inductor and the Schottky diode and charges up the output capacitor. Both Schottky diodes in the LT3466-1 can sustain a maximum of 1A current. The selection of inductor and capacitor value should ensure the peak of the inrush current to be below 1A. For low DCR inductors, which is usually the case for this application, the peak inrush current can be simplified as follows: IPK = VIN – 0.6 ωL where: ω= 1 LCOUT Table 3 gives inrush peak current for some component selections. Table 3. Inrush Peak Current 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 34661f 11 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). RFB1 = 200mV ILED1 Using a Filtered PWM Signal A variable duty cycle PWM can be used to control the brightness of the LED string. The PWM signal is filtered (Figure 8) by an RC network and fed to the CTRL1 pin. The corner frequency of R1, C1 should be much lower than the frequency of the PWM signal. R1 needs to be much smaller than the internal impedance in the CTRL pin, which is 100kΩ. PWM 10kHz TYP Table 4. RFB1 Value Selection ILED1 (mA) Feedback voltage variation versus control voltage is given in the Typical Performance Characteristics graphs. RFB1 (Ω) 5 40.2 10 20.0 15 13.3 20 10.0 25 8.06 Most White LEDs are driven at maximum currents of 15mA to 20mA. DIMMING WHITE LEDS The LED current in the driver can be set by modulating the CTRL1 pin. There are two different ways to control the intensity of white LEDs. Using a DC Voltage For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The CTRL1 pin voltage can be modulated to set the dimming of the LED string. As the voltage on the CTRL1 pin increases from 0V to 1.8V, the LED current increases from 0 to ILED1. As the CTRL1 pin voltage increases beyond 1.8V, it has no effect on the LED current. The LED current can be set by: LT3466-1 R1 10k CTRL1 C1 1µF 34661 F08 Figure 8. Dimming Control Using a Filtered PWM Signal SETTING THE BOOST OUTPUT VOLTAGE The LT3466-1 regulates the voltage at the FB2 pin to 0.8V. The output voltage of the boost converter (VOUT2) is set by a resistor divider according to the formula: ⎛ R1⎞ VOUT2 = 0.8V ⎜ 1+ ⎟ ⎝ R2⎠ Choose 1% resistors for better accuracy. The FB2 input bias current is quite low, on the order of 10nA (typ). Large resistor values (R1 ~ 1MΩ) can be used in the divider network maximizing efficiency. PROGRAMMING THE BOOST OUTPUT VOLTAGE The output voltage of the boost converter can be modulated by applying a variable DC voltage at the CTRL2 pin The nominal voltage at the FB2 pin is 800mV. As the voltage on the CTRL2 pin is ramped from 0V to 1V, the FB2 pin voltage ramps up to 0.8V. The feedback voltage can be programmed as: ILED1 ≈ (VCTRL1/5 • RFB1), when VCTRL1 < 1V VFB2 ≈ VCTRL2, when VCTRL2 < 0.8V ILED1 ≈ (200mV/RFB1), when VCTRL1 > 1.8V VFB2 ≈ 0.8V, when VCTRL2 > 1V 34661f 12 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). Connect the CTRL2 pin to ground to disable converter 2. Do not leave the pin floating. Unlike the CTRL1 pin, which has an internal 100k pull-down resistor, the CTRL2 pin input impedance is very high (>100MΩ). A small amount of board leakage current is sufficient to turn on the converter 2. VIN SW2 FB1 CTRL1 OFF ON 16V 30mA COUT3 0.47µF R1 475k COUT2 0.47µF LT3466-1 RFB1 10Ω RBASE Q1 + – VCE(SAT) VOUT2 VOUT1 COUT1 1µF IBASE FB2 RT R2 24.9k CTRL2 OFF ON 63.4k 1% 34661 F10 CIN: TAIYO YUDEN JMK107BJ105 COUT1: TAIYO YUDEN GMK316BJ105 COUT2, COUT3: TAIYO YUDEN TMK316BJ474 L1, L2: TOKO D52LC Q1: PHILIPS BC807 Figure 10. Li-Ion Powered Driver for 6 White LEDs and a Secondary OLED Display with Output Disconnect 900 VIN = 3.6V 800 VOUT2 = 16V The RBASE resistor can be calculated as: ILOAD = 30mA 700 VFB2 (mV) 600 IBASE = 500 400 ILOAD 0 . 4hFE(MIN) 300 IBASE must be chosen such that Q1 is in saturation under all conditions. The hFE(MIN) can be obtained from the Philips BC807 data sheet as: 200 100 0 0 0.4 0.8 1.2 VCTRL2 (V) 1.6 2 34661 F09 Figure 9. VFB2 vs VCTRL2 OUTPUT DISCONNECT The LT3466-1 can be used for powering white LEDs (Channel 1) and an OLED display or, LCD bias (Channel 2). Some OLED displays require load isolation in order to reduce the current drained from the battery in shutdown. The LT3466-1 output can be configured to provide output disconnect by the use of only one resistor, RBASE, and a PNP transistor, Q1, as shown in Figure 10. hFE(MIN) ≅ 100 This yields worst case IBASE as: IBASE = 30mA ≅ 0 . 75mA 0 . 4(100) RBASE is given by: VIN(MAX ) + IBASE • RBASE + VBE(Q1) = VOUT 2 + VCE(Q1) Thus; RBASE = VOUT 2 – VIN(MAX ) + VCE(Q1) – VBE(Q1) IBASE As a design example, we target a Li-Ion powered driver for 6 white LEDs and an OLED display (16V at 30mA). We can choose a general purpose PNP switching transistor like Philips BC807 (Q1) to provide isolation. 34661f 13 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 = 13.6k Picking the closest 1% resistor value yields: RBASE = 14k GND COUT1 RFB1 BOARD LAYOUT CONSIDERATION As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To prevent electromagnetic interference (EMI) problems, proper layout of high frequency switching paths is essential. Minimize the length and area of all traces connected to the switching node pins (SW1 and SW2). Keep the feedback pins (FB1 and FB2) away from the switching nodes. The DFN package has an exposed paddle that must be connected to the system ground. The ground connection for the feedback resistors should be tied directly to the CIN 10 1 L1 3 L2 CTRL1 9 2 VIN RT 11 8 4 7 5 6 R2 CTRL2 R1 COUT2 34661 F10 GND Figure 11. Recommended Component Placement 34661f 14 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 38.3k 1% OFF ON 4 LEDs/20mA VOUT2 = 12V 85 EFFICIENCY (%) L1 15µH 90 12V 30mA AT VIN = 3V 60mA AT VIN = 5V VIN = 5V 80 VIN = 3V 75 70 65 34661 TA01a 60 CIN: TAIYO YUDEN JMK107BJ105 COUT1: TAIYO YUDEN EMK212BJ474 COUT2: TAIYO YUDEN EMK212BJ105 L1, L2: MURATA LQH32CN150K53 0 10 20 30 40 LOAD CURRENT (mA) 50 60 34661 TA01b Li-Ion Powered Driver for 6 White LEDs and OLED Display 3V TO 5V L1 33µH SW1 L2 33µH VIN Conversion Efficiency 1µF 90 85 SW2 LED DRIVER 6 LEDs COUT1 1µF VOUT1 LT3466-1 COUT2 1µF FB1 FB2 RT GND CTRL1 RFB1 10Ω VOUT2 SHUTDOWN AND DIMMING CONTROL 1 63.4k CIN: TAIYO YUDEN JMK107BJ105 COUT1, COUT2: TAIYO YUDEN GMK316BJ105 L1, L2: 33µH TOKO D52LC 16V 30mA R1 475k EFFICIENCY (%) 80 BOOST CONVERTER 75 70 65 60 VIN = 3.6V 6 LEDs VOUT2 = 16V CTRL2 SHUTDOWN AND DIMMING CONTROL 2 R2 24.9k 34661 TA02a 55 50 0 5 10 15 20 25 30 OUTPUT CURRENT (mA) 34661 TA02b 34661f 15 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 63.4k 1% OFF ON 34661 TA03a CIN: TAIYO YUDEN JMK107BJ105 COUT1: TAIYO YUDEN GMK316BJ105 COUT2, COUT3: TAIYO YUDEN TMK316BJ474 L1, L2: 33µH TOKO D52LC Q1: PHILIPS BC807 Conversion Efficiency 90 VOUT2 20V/DIV VIN = 3.6V VOUT2 = 16V EFFICIENCY (%) 80 IL2 200mA/DIV CTRL2 5V/DIV VIN = 3.6V VOUT2 = 16V 2ms/DIV 34661 TA03c 70 60 50 40 0 5 10 15 20 LOAD CURRENT (mA) 25 30 34661 TA03b 34661f 16 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 63.4k 1% CIN: TAIYO YUDEN JMK107BJ105 COUT1: TAIYO YUDEN GMK316BJ105 COUT2, COUT3: TAIYO YUDEN TMK316BJ474 L1, L2: 33µH TOKO D52LC Q1: SILICONIX TPO610 OFF ON 34661 TA04a NOTE: ENSURE THAT VOUT2 > VIN(MAX) + 5V Conversion Efficiency 90 VIN = 3.6V 85 VOUT2 = 16V VOUT2 20V/DIV EFFICIENCY (%) 80 IL2 200mA/DIV CTRL2 5V/DIV 75 70 65 60 VIN = 3.6V VOUT2 = 16V 2ms/DIV 34661 TA04c 55 50 0 5 10 20 15 LOAD CURRENT (mA) 25 30 34661 TA04b 34661f 17 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 16.5Ω CTRL1 OFF ON FB2 RT CTRL2 147k COUT3 1µF 10k OFF ON CIN: TAIYO YUDEN JMK107BJ105 COUT1: TAIYO YUDEN UMK325BJ105 COUT2, COUT3: TAIYO YUDEN GMK316BJ105 C1, C2: TAIYO YUDEN UMK212BJ104 D1, D2: PHILIPS BAT54S L1: 68µH TOKO D52LC L2: 33µF TOKO D52LC 34661 TA05a Conversion Efficiency 84 +8V OUTPUT 10V/DIV VIN = 3.6V 10 LEDs +8V/10mA –8V/10mA EFFICIENCY (%) 82 –8V OUTPUT 10V/DIV CTRL2 5V/DIV VIN = 3.6V +8V/10mA –8V/10mA 2ms/DIV 34661 TA05c 80 78 76 74 72 0 2 4 6 8 LED CURRENT (mA) 10 12 34661 TA05b 34661f 18 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. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 34661f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 19 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 0.1µF EFFICIENCY (%) CIN 1µF 82 80 78 76 OFF ON 74 34661 TA06a CIN: TAIYO YUDEN JMK107BJ105 COUT1, COUT2, COUT3: TAIYO YUDEN GMK316BJ105 C1: TAIYO YUDEN UMK212BJ104 L1, L2: 33µH TOKO D52LC D1: PHILIPS BAT54S 0 2.5 5 7.5 10 LED CURRENT (mA) 12.5 15 34661 TA06b RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1618 Constant Current, Constant Voltage 1.4MHz, High Efficiency Boost Regulator VIN: 1.6V to 18V, VOUT(MAX) = 34V, IQ = 1.8mA, ISD < 1µA, MS/EDD Packages LT1932 Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator VIN: 1V to 10V, VOUT(MAX) = 34V, IQ = 1.2mA, ISD < 1µA, ThinSOTTM Package LT1937 Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator VIN: 2.5V to 10V, VOUT(MAX) = 34V, IQ = 1.9mA, ISD < 1µA, ThinSOT, SC70 Packages LTC®3200-5 Low Noise, 2MHz, Regulated Charge Pump White LED Driver VIN: 2.7V to 4.5V, VOUT(MAX) = 5V, IQ = 8mA, ISD < 1µA, ThinSOT Package LTC3202 Low Noise, 1.5MHz, Regulated Charge Pump White LED Driver VIN: 2.7V to 4.5V, VOUT(MAX) = 5.5V, IQ = 5mA, ISD < 1µA, MS/EDD Packages LTC3205 High Efficiency, Multidisplay LED Controller VIN: 2.8V to 4.5V, VOUT(MAX) = 6V, IQ = 50µA, ISD < 1µA, QFN-24 Package LTC3216 1A Low Noise High Current LED Charge Pump with Independent Flash/Torch Current Control VIN: 2.9V to 4.4V, VOUT(MAX) = 5.5V, IQ = 300µA, ISD < 2.5µA, DFN Package LTC3453 500mA Synchronous Buck-Boost High Current LED Driver in Q FN VIN: 2.7V to 5.5V, VOUT(MAX) = 5.5V, IQ = 0.6mA, ISD < 6µA, QFN Package LT3465/LT3465A Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED Boost Regulator with Integrated Schottky Diode VIN: 2.7V to 16V, VOUT(MAX) = 34V, IQ = 1.9mA, ISD < 1µA, ThinSOT Package LT3466 Dual Constant Current, 2MHz High Efficiency White LED Boost Regulator with Integrated Schottky Diode VIN: 2.7V to 24V, VOUT(MAX) = 40V, IQ = 5mA, ISD < 16µA, DFN Package LT3479 3A, Full Featured DC/DC Converter with Soft-Start and Inrush Current Protection VIN: 2.5V to 24V, VOUT(MAX) = 40V, IQ = 6.5mA, ISD < 1µA, DFN/TSSOP Packages ThinSOT is a trademark of Linear Technology Corporation. 34661f 20 Linear Technology Corporation LT/TP 0705 500 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005