The R5511x Series are CMOS-based voltage regulator(LDO) ICs equipped with a voltage detector(VD). LDO function of the R5511x has features of high ripple rejection, low dropout voltage, high output voltage accuracy, and low supply current. Each of these ICs consists of a voltage reference unit, an error amplifier, resistors for setting output voltage, a current limit circuit, a voltage detector, and a chip enable circuit. The output of built-in voltage detector is Nch open drain type. (With the mask option CMOS output type is also available.) The output voltage and the detector threshold voltage are fixed in the IC. Low supply current by the merit of CMOS process and the built-in transistor with low ON-resistance make low dropout voltage. These regulators in the R5511x Series are remarkable improvement on the current regulators in terms of ripple rejection, input transient response, and load transient response. Furthermore, the R5511x series can supervise input voltage (the input voltage means the input level for VDD or VSEN pin) with built-in detector. Thus, the R5511x series are suitable not only for cellular handsets but also for power supply for CD-drives, DVD-drives, and so forth. Since the packages for these ICs are the SON-6, SOT-23-5, SOT-89-5 package, high density mounting of the ICs on boards is possible.