S-8550/8551 Series STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS www.sii-ic.com Seiko Instruments Inc., 2007-2010 Rev.4.0 00 The S-8550/8551 Series is a CMOS synchronous rectification step-down switching regulator which mainly consists of a reference voltage circuit, an oscillator, an error amplifier, a phase compensation circuit, a PWM controller, an under voltage lockout circuit (UVLO), a current limit circuit, and a power MOS FET. The oscillation frequency is high at 1.2 MHz, so a high efficiency, large output current, step-down switching regulator can be achieved by using small external parts. The built-in synchronous rectification circuit makes achieving high efficiency easier compared with conventional step-down switching regulators. A ceramic capacitor can be used as an output capacitor. High-density mounting is supported by adopting packages small SOT-23-5 and super-small and thin SNT-8A. The S-8550 and S-8551 Series are offered according to different pin configuration. Features Oscillation frequency : 1.2 MHz Input voltage range : 2.0 V to 5.5 V Output voltage range : Arbitrarily settable by external output voltage setting resistor Output current : 600 mA Reference voltage : 0.6 V 2.0% Efficiency : 92% Soft-start function : 1 ms typ. Shutdown function : Shutdown current consumption : 1.0 A max. Built-in current limit circuit Pch power MOS FET on-resistance : 0.4 typ. Nch power MOS FET on-resistance : 0.3 typ. Constant continuous mode operation (no light load mode) *1 Lead-free, Sn 100%, halogen-free *1. Refer to Product Name Structure for details. Applications Mobile devices, such as mobile phones, Bluetooth devices, wireless devices, digital audio players, digital still cameras, portable DVD players, and portable CD players Packages SOT-23-5 SNT-8A Seiko Instruments Inc. 1 STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS S-8550/8551 Series Rev.4.0 00 Block Diagram 1. SOT-23-5 VIN Current limit circuit IC internal power supply Error amplifier FB + PWM control *1 + circuit V OUT CONT Reference PWM comparator voltage L Triangular wave R FB1 *1 C FB generation circuit C OUT R ON/OFF FB2 UVLO V C circuit IN IN circuit ON/OFF VSS *1. Parasitic diode Figure 1 2. SNT-8A VIN Current limit circuit IC internal power supply Error amplifier FB + PWM control *1 + circuit V CONT OUT Reference PWM comparator voltage L Triangular wave R FB1 *1 C generation FB circuit C OUT ON/OFF R UVLO FB2 circuit V C circuit IN IN ON/OFF VSS PVSS *1. Parasitic diode Figure 2 2 Seiko Instruments Inc.