Final Electrical Specifications LT3465A 2.4MHz White LED Step-Up Converter with Built-In Schottky in ThinSOTTM August 2003 U FEATURES DESCRIPTIO Inherently Matched LED Current Drives Up to Six LEDs from a 3.6V Supply No External Schottky Diode Required Open LED Protection High Efficiency: 79% Typical Requires Only 0.22F Output Capacitor Switching Frequency Above AM Broadcast Band Low Profile (<1mm) SOT-23 Packaging U APPLICATIO S The LT(R)3465A is a step-up DC/DC converter designed to drive up to six LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents and eliminates the need for ballast resistors. This device integrates the Schottky diode required externally on competing devices. Additional features include output voltage limiting when LEDs are disconnected, one-pin shutdown and dimming control. The LT3465A switches at 2.4MHz, allowing the use of tiny external components. Constant frequency switching results in low input noise and a small output capacitor. Just 0.22F is required for 3-, 4- or 5-LED applications. Cellular Phones PDAs, Handheld Computers Digital Cameras MP3 Players GPS Receivers The LT3465A is available in a low profile (<1mm) 6-lead SOT-23 package. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. U TYPICAL APPLICATIO Conversion Efficiency L1 22H 80 VIN = 3.6V 78 3V TO 5V 76 SHUTDOWN AND DIMMING CONTROL C1 1F 74 VOUT VIN C2 0.22F LT3465A CTRL FB GND R1 10 EFFICIENCY (%) SW 72 70 68 66 64 C1, C2: X5R OR X7R DIELECTRIC L1: MURATA LQH32CN220 3465A F01a 62 60 Figure 1. Li-Ion Powered Driver for Four White LEDs 0 5 15 10 LED CURRENT (mA) 20 3465A F01b 3465ai 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. 1 LT3465A W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) Input Voltage (VIN) ................................................. 16V SW Voltage ............................................................. 36V FB Voltage ................................................................ 2V CTRL Voltage .......................................................... 10V Operating Temperature Range (Note 2) .. - 40C to 85C Maximum Junction Temperature ......................... 125C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C ORDER PART NUMBER TOP VIEW VOUT 1 6 SW GND 2 5 VIN LT3465AES6 4 CTRL FB 3 S6 PACKAGE 6-LEAD PLASTIC TSOT-23 TJMAX = 125C, JA = 256C/W IN FREE AIR JA = 120C ON BOARD OVER GROUND PLANE JC = 102C/W S6 PART MARKING LTAFT Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3V, VCTRL = 3V, unless otherwise noted. PARAMETER CONDITIONS MIN Minimum Operating Voltage TYP 0C TA 85C 200 212 mV 35 100 nA 1.9 2.0 2.6 3.2 3.3 5.0 mA A 1.8 2.4 2.8 MHz 90 93 % 225 Switching Frequency Switch Current Limit V 10 Not Switching CTRL = 0V Maximum Duty Cycle 16 188 FB Pin Bias Current Supply Current UNITS V Maximum Operating Voltage Feedback Voltage MAX 2.7 340 mA Switch VCESAT ISW = 250mA 300 mV Switch Leakage Current VSW = 5V 0.01 VCTRL for Full LED Current 5 A 50 mV 72 60 90 A A A 1.8 V VCTRL to Shut Down Device CTRL Pin Bias Current TA = 85C TA = -40C Schottky Forward Drop ID = 150mA Schottky Leakage Current VR = 30V 48 40 60 60 50 75 0.7 V 4 A Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3465AE is guaranteed to meet performance specifications from 0C to 70C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. 3465ai 2 LT3465A U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Saturation Voltage (VCESAT) 300 400 350 300 250 200 150 100 50 0 100 150 200 250 SWITCH CURRENT (mA) 300 250 24 21 200 150 15 9 6 50 3 350 1000 400 600 800 200 SCHOTTKY FORWARD DROP (mV) 0 0 1200 TA = 25C 50 10 8 VIN (V) 12 14 16 Input Current in Output Open Circuit TA = 25C 4 INPUT CURRENT (mA) OUTPUT CLAMP VOLTAGE (V) 100 6 5 30 150 4 3465 G03 Open-Circuit Output Clamp Voltage 35 200 2 3465 G02 VFB vs VCTRL FEEDBACK VOLTAGE (mV) 18 12 100 3465 G01 250 TA = 25C 27 0 50 0 30 TA = 25C IQ (A) TA = 25C SCHOTTKY FORWARD CURRENT (mA) SWITCH SATURATION VOLTAGE (mV) 450 Shutdown Quiescent Current (CTRL = 0V) Schottky Forward Voltage Drop 25 20 15 10 3 2 1 5 0 0 1 0.5 1.5 CONTROL VOLTAGE (V) 0 0 2 2 4 10 8 12 6 INPUT VOLTAGE (V) 3465 G04 14 2.0 16 3.0 3.5 4.0 INPUT VOLTAGE (V) 4.5 5.0 3465 G06 3465 G05 Switching Waveforms Switching Frequency Feedback Voltage 210 3.0 VSW 10V/DIV 2.5 VOUT 50mV/DIV VIN = 3.6V 4 LEDs 20mA, 22H 100ns/DIV 3465 G07 FEEDBACK VOLTAGE (mV) IL 50mA/DIV SWITCHING FREQUENCY (MHz) 208 2.5 2.0 1.5 1.0 0.5 206 204 202 200 198 196 194 192 0 -50 0 50 TEMPERATURE (C) 100 3465 G08 190 -50 -30 -10 10 30 50 TEMPERATURE (C) 70 90 3465 G09 3465ai 3 LT3465A U W TYPICAL PERFOR A CE CHARACTERISTICS Quiescent Current (CTRL = 3V) Switching Current Limit 3.0 400 350 CURRENT LIMIT (mA) 2.5 IQ (mA) 2.0 1.5 1.0 -50C 25C 100C 0.5 5 10 VIN (V) 15 250 200 150 100 -50C 25C 100C 50 0 0 300 0 20 0 20 40 60 DUTY CYCLE (%) 80 3465 G10 3465 G11 VIN = 3.6V, 4 LEDs Schottky Leakage Current 80 8 15mA 78 EFFICIENCY (%) SCHOTTKY LEAKAGE CURRENT (A) 20mA 79 77 76 100 10mA 75 74 73 72 71 70 -50 50 0 TEMPERATURE (C) 7 VR = 25 6 VR = 10 4 3 2 1 0 -50 100 VR = 16 5 0 50 100 TEMPERATURE (C) 3465 G13 3465A G12 U U U PI FU CTIO S VOUT (Pin 1): Output Pin. Connect to output capacitor and LEDs. Minimize trace between this pin and output capacitor to reduce EMI. GND (Pin 2): Ground Pin. Connect directly to local ground plane. FB (Pin 3): Feedback Pin. Reference voltage is 200mV. Connect LEDs and a resistor at this pin. LED current is determined by the resistance and CTRL pin voltage: 200mV When VCTRL > 1.8V RFB V CTRL When VCTRL < 1V 5 * RFB CTRL (Pin 4): Dimming Control and Shutdown Pin. Ground this pin to shut down the device. When VCTRL is greater than about 1.8V, full-scale LED current is generated. When VCTRL is less than 1V, LED current is reduced. VIN (Pin 5): Input Supply Pin. Must be locally bypassed with a 1F X5R or X7R type ceramic capacitor. SW (Pin 6): Switch Pin. Connect inductor here. ILED ILED (1) 3465ai 4 LT3465A W BLOCK DIAGRA VIN FB 5 3 200mV VREF 1.25V - + + 6 SW - A1 COMPARATOR 1 DRIVER RC + A2 R S Q1 Q CC + 0.2 10k CTRL VOUT - RAMP GENERATOR 40k 4 2 GND 3465A F02 2.4MHz OSCILLATOR Figure 2. LT3465A Block Diagram U W U U APPLICATIO S I FOR ATIO Operation The LT3465A 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 in Figure 2. At the start of each oscillator cycle, the SR latch is set, which turns on the power switch Q1. 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 SR latch is reset turning 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 reference voltage of 200mV. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered. The CTRL pin voltage is used to adjust the reference voltage. Minimum Output Current The LT3465A can drive a 3-LED string at 0.2mA 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 details circuit operation driving three white LEDs at a 0.2mA load. Peak inductor current is less than 30mA and the regulator operates in discontinuous mode, meaning the inductor current reaches zero during the discharge phase. After the inductor current reaches zero, the SW 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 300 resistor across the inductor, although this will degrade efficiency. VSW 5V/DIV IL 20mA/DIV VOUT 10mV/DIV VIN = 4.2V ILED = 0.2mA 3 LEDs 0.1s/DIV 3465A F03 Figure 3. Switching Waveforms 3465ai 5 LT3465A U W U U APPLICATIO S I FOR ATIO Inductor Selection Capacitor Selection A 22H or 10H inductor is recommended for most LT3465A applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2MHz and low DCR (copper wire resistance). Some inductors in this category with small size are listed in Table 1. The efficiency comparison of different inductors is shown in Figure 4. The small size of ceramic capacitors makes them ideal for LT3465A applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 1F input capacitor and a 0.22F output capacitor are sufficient for most LT3465A applications. Table 1. Recommended Inductors MANUFACTURER PHONE URL www.t-yuden.com PART NUMBER Taiyo Yuden 408-573-4150 MANUFACTURER Murata 814-237-1431 www.murata.com 250 Murata 814-237-1431 www.murata.com Kemet 408-986-0424 www.kemet.com 160 Panasonic 714-373-7334 www.panasonic.com Inrush Current DCR () CURRENT RATING (mA) LQH32CN220 0.71 ELJPC220KF 4.0 CDRH3D16-220 0.53 350 Sumida 847-956-0666 www.sumida.com LB2012B220M 1.7 75 Taiyo Yuden 408-573-4150 www.t-yuden.com LEM2520-220 5.5 125 Taiyo Yuden 408-573-4150 www.t-yuden.com 80 Table 2. Recommended Ceramic Capacitor Manufacturers The LT3465A has a built-in Schottky diode. When supply voltage is applied to the VIN pin, the voltage difference between VIN and VOUT generates inrush current flowing from input through the inductor and the Schottky diode to charge the output capacitor to VIN. The maximum current the Schottky diode in the LT3465A can sustain is 1A. The selection of inductor and capacitor value should ensure the peak of the inrush current to be below 1A. The peak inrush current can be calculated as follows: IP = VIN = 3.6V 4 LEDS EFFICIENCY (%) 75 = 70 VIN - 0.6 * exp - * a tan * sin a tan L* r + 1.5 2*L (r + 1.5) 1 - = L*C 4 * L2 2 65 MURATA LQH32CN220 MURATA LQH32CN100 MURATA LQH2MCN220 TOKO D312-220 TOKO D312-100 TAIYO YUDEN LB2012B220 60 55 50 0 5 10 15 20 LED CURRENT (mA) 3465 F04 where L is the inductance, r is the resistance of the inductor and C is the output capacitance. For low DCR inductors, which is usually the case for this application, the peak inrush current can be simplified as follows: Figure 4. Efficiency Comparison of Different Inductors IP = VIN - 0.6 * exp - * L* 2 3465ai 6 LT3465A U W U U APPLICATIO S I FOR ATIO Table 3 gives inrush peak currents for some component selections. R1 5k LT3465 PWM C1 100nF Table 3. Inrush Peak Current VIN (V) r () L (H) C (F) IP (A) 5 0.5 22 0.22 0.38 5 0.5 22 1 0.70 3.6 0.5 22 0.22 0.26 5 0.5 33 1 0.60 LED Current and Dimming Control The LED current is controlled by the feedback resistor (R1 in Figure 1) and the feedback reference voltage. ILED = VFB/RFB The CTRL pin sets the feedback reference voltage as shown in the Typical Performance Characteristics. When CTRL is at 1.8V or more, the feedback reference is 200mV, which results in full-scale LED current. The CTRL pin can be used as a dimming control when its voltage is between 200mV to 1.5V. To maintain LED current accuracy, a 1% or better resistor for R1 is recommended. The formula and table for RFB selection are shown below: CTRL 3465 F06 Figure 5. Dimming Control Using a Filtered PWM Signal Dimming Using Direct PWM Unlike the LT3465, the LT3465A does not have internal soft-start. Although the input current is higher during start-up, the absence of soft-start allows the CTRL pin to be directly driven with a PWM signal for dimming. A zero percent duty cycle sets the LED current to zero, while 100% duty cycle sets it to full current. Average LED current increases proportionally with the duty cycle of the PWM signal. PWM frequency should be between 1kHz and 10kHz for best performance. The PWM signal should be at least 1.8V in magnitude; lower voltage will lower the feedback voltage as shown in Equation 1. Waveforms are shown for a 1kHz PWM and 10kHz PWM signal in Figures 6a and 6b respectively. LT3465A RFB = 200mV/ILEDF PWM CTRL where ILEDF is full-scale LED current Table 4. RFB Resistor Value Selection ILED (mA) R1 () 5 40.2 10 20.0 15 13.3 20 10.0 FB 100mV/DIV CTRL 2V/DIV 200s/DIV (1kHz) Dimming Using Filtered PWM Dimming can be realized by using an RC filter in front of the CTRL pin to filter a PWM signal, as depicted in Figure 5. The filtered PWM signal is equivalent to a constant voltage. The time constant R1 * C1 should be much lower than the frequency of the PWM signal. Additionally, R1 should be small compared to the 50k impedance of the CTRL pin. Suggested values are shown in Figure 5. 3465A F06a Figure 6a. FB 100mV/DIV CTRL 2V/DIV 20s/DIV (10kHz) 3465A F06b Figure 6b. 3465ai 7 LT3465A U W U U APPLICATIO S I FOR ATIO Open Circuit Protection The LT3465A has an internal open-circuit protection circuit. When the LEDs are disconnected from the circuit or fail open, VOUT is clamped at 30V. The LT3465A will then switch at a low frequency, minimizing input current. VOUT and input current during open circuit are shown in the Typical Performance Characteristics. switching path is essential. Place COUT next to the VOUT pin. Always use a ground plane under the switching regulator to minimize interplane coupling. In addition, the ground connection for the feedback resistor R1 should be tied directly to the GND pin and not shared with any other component, ensuring a clean, noise-free connection. Recommended component placement is shown in Figure 7. Board Layout Consideration Start-Up Input Current As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency As previously mentioned, the LT3465A does not have an internal soft-start circuit. Inrush current can therefore rise to approximately 400mA as shown in Figure 8 when driving 4 LEDs. The LT3465 has an internal soft-start circuit and is recommended if inrush current must be minimized. GND IIN 200mV/DIV COUT L RFB 1 6 2 5 3 4 FB 200mV/DIV CIN VIN CTRL CTRL 2V/DIV 50s/DIV 3465A F06b 3465 F07 Figure 7. Recommended Component Placement Figure 8. 3465ai 8 LT3465A U TYPICAL APPLICATIO S Li-Ion to Two White LEDs 85 L1 22H 3V TO 5V VIN = 3.6V 2 LEDS 80 VOUT VIN CIN 1F COUT 1F LT3465A CTRL FB EFFICIENCY (%) 75 SW R1 4 GND 70 65 60 3465 TA01a 55 CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603ZD105 L1: MURATA LQH32CN220 50 0 10 30 20 LED CURRENT (mA) 40 50 3465 TA01b Li-Ion to Three White LEDs L1 22H 85 3V TO 5V VIN = 3.6V 3 LEDS 80 CIN 1F 75 VOUT VIN COUT 0.22F LT3465A CTRL FB GND R1 10 EFFICIENCY (%) SW 70 65 60 3465 TA02a CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603YD224 L1: MURATA LQH32CN220 55 50 0 5 15 10 LED CURRENT (mA) 20 3465 TA02b 3465ai 9 LT3465A U TYPICAL APPLICATIO S Li-Ion to Five White LEDs L1 22H 3V TO 5V SW VOUT VIN CIN 1F COUT 0.22F LT3465A CTRL FB GND R1 10 3465 TA03a CIN: TAIYO YUDEN JMK107BJ105 COUT: TAIYO YUDEN GMK212BJ224 L1: MURATA LQH32CN220 80 VIN = 3.6V 5 LEDS EFFICIENCY (%) 75 70 65 60 55 50 0 5 15 10 LED CURRENT (mA) 20 3465 TA03b 3465ai 10 LT3465A U PACKAGE DESCRIPTIO S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 0.62 MAX 2.90 BSC (NOTE 4) 0.95 REF 1.22 REF 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC 1.50 - 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 - 0.45 6 PLCS (NOTE 3) 0.95 BSC 0.80 - 0.90 0.20 BSC 0.01 - 0.10 1.00 MAX DATUM `A' 0.30 - 0.50 REF 0.09 - 0.20 (NOTE 3) 1.90 BSC S6 TSOT-23 0302 NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 3465ai 11 LT3465A U TYPICAL APPLICATIO Li-Ion to Six White LEDs L1 22H 80 VIN = 3.6V 6 LEDS 3V TO 5V SW CIN 1F VOUT VIN COUT 0.47F LT3465A CTRL FB R1 10 GND EFFICIENCY (%) 75 70 65 60 3465 TA04a 55 CIN: TAIYO YUDEN JMK107BJ105 COUT: TDK 2012X7R1E474K L1: MURATA LQH32CN220 50 0 5 15 10 LED CURRENT (mA) 20 3465 TA04b RELATED PARTS PART NUMBER DESCRIPTION LT1618 Constant Current, Constant Voltage, 1.4MHz, High Efficiency Boost Regulator LT1932 Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator LT1937 Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator LTC(R)3200-5 Low Noise, 2MHz, Regulated Charge Pump White LED Driver LTC3200 LTC3201 LTC3202 LTC3404 LTC3405 LTC3405A LTC3406 LTC3406B LT3407 LTC3412 LTC3440 LTC3465 COMMENTS Up to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX): 34V, IQ: 1.8mA, ISD: <1A, 10-Lead MS Package Up to 8 White LEDs, VIN: 1V to 10V, VOUT(MAX): 34V, IQ: 1.2mA, ISD: <1A, ThinSOT Package Up to 4 White LEDs, VIN: 2.5V to 10V, VOUT(MAX): 34V, IQ: 1.9mA, ISD: <1A, ThinSOT, SC70 Packages Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ: 8mA, ISD: <1A, ThinSOT Package Low Noise, 2MHz, Regulated Charge Pump White LED Driver Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ: 8mA, ISD: <1A, 10-Lead MS Package Low Noise, 1.7MHz, Regulated Charge Pump White LED Driver Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ: 6.5mA, ISD: <1A, 10-Lead MS Package Low Noise, 1.5MHz, Regulated Charge Pump White LED Driver Up to 8 White LEDs, VIN: 2.7V to 4.5V, IQ: 5mA, ISD: <1A, 10-Lead MS Package 600mA (IOUT), 1.4MHz Synchronous Step-Down 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN): 0.8V, IQ: 10A, ISD: <1A, DC/DC Converter MS8 Package 300mA (IOUT), 1.5MHz Synchronous Step-Down 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN): 0.8V, IQ: 20A, ISD: <1A, DC/DC Converters ThinSOT Package 600mA (IOUT), 1.5MHz Synchronous Step-Down 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.6V, IQ: 20A, DC/DC Converters ISD: <1A, ThinSOT Package Dual 600mA (IOUT), 1.5MHz Synchronous Step-Down 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.6V, IQ: 40A, DC/DC Converter ISD: <1A, MS Package 2.5A (IOUT), 4MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.8V, IQ: 60A, ISD: <1A, TSSOP16E Package 600mA (IOUT), 2MHz Synchronous Buck-Boost 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 2.5V, IQ: 25A, DC/DC Converter ISD: <1A, 10-Lead MS Package Constant Current, 1.2MHz, High Efficiency White LED Up to 5 White LEDs, VIN: 2.7V to 16V, IQ: 1.9A, Boost Regulator ISD: <1A, ThinSOT Package 3465ai 12 Linear Technology Corporation LT/TP 0803 1.5K * PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com LINEAR TECHNOLOGY CORPORATION 2003