The XC6221 series is a high accuracy, low noise, high speed, low dropout CMOS regulator with high ripple rejection. The series includes a reference voltage source, an error amplifier, a current limiter, and a phase compensation circuit. The CE function enables the entire circuit to be in stand-by state by inputting low level signal. In this stand-by mode, the electric charge at the output capacitor (CL) will be discharged by the internal auto-discharge switch, and as a result the VOUT pin quickly returns to the VSS level. The output stabilization capacitor (CL) is also compatible with low ESR ceramic capacitors. Output voltage is selectable in 0.05V increments within a range of 0.8V~5.0V, using the laser trimming technology set in factory. The current limiter's fold-back circuit also operates as a short circuit protection and an output current limiter at the output pin. The series achieves a fast response with only 25A of low power consumption. Also the series has low dropout voltage characteristics, which is 80mV at IOUT=100mA and VOUT=3.0V. With the use of small USP-4 and ultra small USPN-4 packages, a small footprint circuit can be designed.