AN734

AN734 Vishay Siliconix Design Guidelines for the Low-Noise Low-Dropout Regulator—Si9181 Nitin Kalje INTRODUCTION This application note discusses the operation and features of the Si9181, a 350-mA CMOS low-dropout (LDO), low-noise voltage regulator. Providing very low ground current to extend battery life, the Si9181 also offers superior line/load transient response and ripple rejection. Designed to maintain regulation while delivering currents from 0 mA to 600 mA, the Si9181 regulator also features an “out of regulation” error flag signal and ON/OFF control input for complete shutdown. The Si9181 was designed for applications requiring a regulated voltage equal to or less than the voltage of the source or battery, and requiring very low output noise. Such applications include digital signal processors, baseband circuits, mixers, Ato-D converters, or intermediate amplifiers. The Si9181’s LDO characteristics are determined by its voltage, ground current, power-dissipation, peak current capability, noise and ripple rejection specifications. The Si9181 is designed to meet the criteria for high quality on each of these determinants, and is suitable for portable and noise–sensitive appliances such as cellular phones. CNOISE 6 4 VIN CIN 2.2 mF ADJ 1 CNOISE S19181 R2 VADJ 8 SD ON OFF 6 MW 60 mV 5% VREF + – 2.2 mA + + – U2 Q2 U3 + 3 GND 1.215 V VREF – – + 7 R1 U1 To VIN Q1 2 CDELAY 0.1 mF ERROR 5 COUT 2.2 mF REXT VOUT FIGURE 1. 350-mA CMOS LDO Regulator (Adjustable Outpu...