Description Features The SE3506 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive two, three, four, or five LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED current resulting in uniform brightness and eliminating the need for ballast resistors. The SE3506 switches at 1MHz, allowing the use of any tiny external components. The output capacitor can be as small as 1μF, saving space and cost versus alternative solutions. A low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. SE3506 is available in low profile SOT-23-5L package. ¾ Inherently Matched LED Current. ¾ High Efficiency: 85% Typical. ¾ Drives Up to Four LEDs from a 3.0V Supply. ¾ Drives Up to Six LEDs from a 3.6V Supply. ¾ Fast 1MHz Switching Frequency. ¾ Uses Tiny 1mm Tall Inductors. ¾ Requires Only 1μF Output Capacitor. ¾ Low Profile SOT-23-5L Packaging. ¾ 100% Lead (Pb)-Free. Application ¾ Cellular Phones ¾ PDAs, Handheld Computuers ¾ Digital Camera ¾ MP3 Players ¾ GPS Receivers Ordering/Marking Information Package Ordering Information Marking Information SOT-23-5L SE3506-LF 506z • The last character is the batch number. Application Diagram Revision 12/4/2008 Preliminary and all contents are subject to change without prior notice © Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 1 Absolute Maximum Rating (1) Parameter Symbol Value Units Input Voltage VIN +5.5 V Switch Voltage VSW +30 V Feedback Voltage VFB +5.5 V Enable Voltage VEN +5.5 V Thermal Resistance, Junction-to-Ambient ΘJA 250 (SOT-23-5) °C/W 260 °C Lead Temperature (Soldering, 10 sec.) Junction Temperature TJ 125 °C Storage Temperature TS -65 to +150 °C Operating Rating (2) Parameter Symbol Value Units Supply Input Voltage VIN +2.7V to +4.5 V Junction Temperature TJ 0 to +125 °C -40 to +85 °C Extended Commercial Operating Temperature Electrical Characteristics VIN = VEN = 3.6V; CIN = COUT = 1μF; TJ = 25°C; unless otherwise specified Symbol VIN Parameter Input Voltage Range VFB Feedback Voltage IFB FB Pin Bias Current ICC Supply Current VTH(EN) IEN Min 2.7 Typ -- Max 4.5 Unit V 80 95 110 mV -- 45 200 nA 70 100 160 μA VEN = 0V -- 0.1 6 μA Switching Frequency VEN = 4.2V 0.7 1.0 1.3 MHz Maximum Duty Cycle VEN = 4.2V -- 90 -- % Switch Leakage Current VSW = 5V 0.1 6 μA Enable Input Threshold Voltage Conditions ISW = 100mA, Duty Cycle = 66% Voltage Raising, Output Turns On, Logic High 1.6 -- -- Voltage Falling, Output Turns Off, Logic Low -- -- 0.4 -- 45 200- Enable Pin Bias Current Note 1: Exceeding the absolute maximum rating may damage the device. Note 2: The device is not guaranteed to function outside its operating rating. The SE3506 is guaranteed to meet specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Revision 12/4/2008 Preliminary and all contents are subject to change without prior notice © Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 2 V nA Application Hints Inductor Selection LED Current Control A 10µH inductor is recommended for most SE3506 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1MHz and low DCR (copper wire resistance). It should also be noted that the Maximum current rating of the inductor should not be exceeded in applications. Typically 100mA to 200mA rating is sufficient for most applications. The LED current is controlled by the feedback resistor (R1). The feedback reference is internally set at 95mV. The LED current is then determined by the equation: 95mV/R1. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table for R1 selection are shown below. R1 = 95mV/ILED Capacitor Selection The small size of ceramic capacitors makes them ideal for SE3506 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 1µF input capacitor and a 1µF output capacitor are sufficient for most SE3506 applications. R1 Resistor Value Selection ILED (mA) 5 10 12 15 20 R1 (Ω) 19.1 9.53 7.87 6.34 4.75 Open-Circuit Protection Diode Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for SE3506 applications. The forward voltage drop of a Schottky diode represents the conduction losses in the diode, while the diode capacitance (CT or CD) represents the switching losses. For diode selection, both forward voltage drop and diode capacitance need to be considered. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant switching losses at the 1MHz switching frequency of the SE3506. A Schottky diode rated at 100mA to 200mA is sufficient for most SE3506 applications. In the cases of output open circuit, such as when the LEDs are disconnected from the circuit or the LEDs fail, the feedback voltage will drop to zero. The SE3506 will then switch at a high duty cycle resulting in a high output voltage, which may cause the SW pin voltage to exceed its maximum 30V rating. A Zener diode can be used at the output to limit the voltage on the SW pin. The Zener voltage should be larger than the maximum forward voltage of the LED string. For example, a Four-LED string can be protected by a Zener diode with a breakdown voltage greater than 16V and less than 30V. The current rating of the zener should be larger than 10mA. LED Driver with Open-Circuit Protection Revision 12/4/2008 Preliminary and all contents are subject to change without prior notice © Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 3 Dimming Control There are two different types of dimming control circuits: 1. Using a PWM Signal to EN Pin 2. Using a DC Voltage With the PWM signal applied to the EN pin, the SE3506 is For some applications, the preferred method of turned on or off by the PWM signal. The LEDs operate at brightness control is a variable DC voltage to adjust either zero or full current. The average LED current the LED current. The dimming control using a DC increases proportionally with the duty cycle of the PWM voltage is shown below. As the DC voltage signal. A 0% duty cycle will turn off the SE3506 and increases, the voltage drop on R2 increases and corresponds to zero LED current. A 100% duty cycle the voltage drop on R1 decreases. Thus, the LED corresponds to full current. The typical frequency range of current decreases. The selection of R2 and R3 will the PWM signal is 1kHz to 5kHz. The magnitude of the make the current from the variable DC source much PWM signal should be higher than the minimum EN smaller than the LED current and much larger than voltage high. The switching waveforms of the EN pin PWM the FB pin bias current. For VDC range from 0V to control are shown below. 2V, the selection of resistors gives dimming control of LED current from 0mA to 15mA. Revision 12/4/2008 Preliminary and all contents are subject to change without prior notice © Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 4 Two LED Efficiency Three LED Efficiency 90% 95% VIN=3.6V 90% EFFICIENCY EFFICIENCY VIN=3.6V VIN=3V 85% 80% 85% VIN=3V 80% 75% 75% 0 5 10 15 20 CURRENT (mA) 25 0 30 5 10 15 20 CURRENT (mA) 30 Five LED Efficiency Four LED Efficiency 90% 90% VIN=3.6V VIN=5V 85% 85% EFFICIENCY EFFICIENCY 25 VIN=3V 80% 75% 70% 80% VIN=3.6V 75% 70% 65% 0 5 10 15 0 5 10 15 CURRENT (mA) CURRENT (mA) VFB VS. ILOAD Six LED Efficiency 85% 80% 2LED 3LED 4LED 97 VIN=3.6V 75% VFB (mV) EFFICIENCY 99 VIN=5V 70% 65% 60% 95 93 91 0 5 10 CURRENT (mA) 15 5 10 15 ILOAD (mA) Revision 12/4/2008 Preliminary and all contents are subject to change without prior notice © Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 5 20 OUTLINE DRAWING SOT-23-5L DIMENSIONS INCHES MM MIN MAX MIN MAX K B H D A F E C J DIMN A B C D E F H J K 0.110 0.059 0.036 0.014 0.0035 0.102 0.120 0.070 0.051 0.020 0.037 0.075 0.006 0.008 0.118 Customer Support Seaward Electronics Incorporated – China Rm 1605, Building 1, International Pioneering Park, #1 Shangdi Xinxi Rd Haidian District, Beijing 100085, China Tel: 86-10-28289-5700 Fax: 86-10-8289-5706 Seaward Electronics Incorporated – Taiwan 2F, #181, Sec. 3, Mincyuan East Rd, Taipei, Taiwan R.O.C Tel: 886-2-2712-0307 Fax: 886-2-2712-0191 Seaward Electronics Incorporated – North America 1512 Centre Pointe Dr. Milpitas, CA95035, USA Tel: 1-408-821-6600 Last Updated - 12/4/2008 Revision 12/4/2008 Preliminary and all contents are subject to change without prior notice © Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 6 2.80 1.50 0.90 0.35 0.090 2.60 3.05 1.75 1.30 0.50 0.95 1.90 0.15 0.20 3.00