AP5725 WHITE LED STEP-UP CONVERTER Description Pin Assignments (Top View) The AP5725 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The 1 6 VIN (Top View) SW device can drive 2 ~ 6 LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED SW 1 6 GND currents resulting in uniform brightness and eliminates the GND 2 5 OVP need for ballast resistors. For driving higher number of LEDs, 2 5 V FB IN AP5725 also supports a single feedback of parallel 74 FB 3 EN 3 4 OVP EN connected multiple strings of equal number of LEDs. SOT26 / TSOT23-6 DFN2020C-6 The AP5725 switches at 1.2MHz that allows the use of tiny external components. A low 0.25V feedback voltage minimizes power loss in the current setting resistor for better efficiency. Features Applications High efficiency: 84% typical Cellular Phones Fast 1.2MHz switching frequency PDAs, Hand held Computers Current limit and UVLO protections Digital Cameras Internal thermal shutdown MP3 Players Internal Over Voltage Protection GPS Receivers Integrated soft-start function SOT26, TSOT23-6 and DFN2020C-6: Available in Green Molding Compound (No Br, Sb) Lead Free Finish/ RoHS Compliant (Note 1) Notes: 1. EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at - + AP5725 WHITE LED STEP-UP CONVERTER Pin Descriptions Pin Name Description SW Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. GND GND pin. Feedback Pin. Reference voltage is 0.25V. Connect cathode of lowest LED and a sense FB resister here. Calculate resistor value according to the formula: R = 0.25V / ILED SET Converter On/Off Control Input. A high input at EN turns the converter On, and a low input EN turns it off. If On/Off control is not needed, connect EN to the input source for automatic startup. The EN pin cannot be left floating. OVP Output Voltage detect pin for over voltage protection. V Input Supply Pin. Must be locally bypassed with 1 F or 2.2 F to reduce input noise. IN Functional Block Diagram OVP 5 1 SW Comparator Driver A2 Q1 CONTROL LOGIC Rc OTP A1 - + Cc FB 3 V REF V 6 IN 0.25V RAMP Generator 2 GND 4 Enable EN 1.2MHz Oscillator 2 of 17 July 2010 AP5725 Diodes Incorporated www.diodes.com Document number: DS31844 Rev. 3 - 2 - +