The ISL9123 is a highly integrated buck switching regulator that is capable of supplying output voltage down to 0.4V. It features an extremely low quiescent current consumption of 950nA in Regulation mode, 140nA in Forced Bypass mode, and 7nA in Shutdown mode. It provides 80% efficiency at 10µA load and has a peak efficiency of 97%. It supports input voltages from 1.8V to 5.5V. The ISL9123 has automatic bypass functionality for situations in which the input voltage is close to the output voltage. In addition to the automatic bypass functionality, the Forced Bypass power saving mode can be chosen if voltage regulation is not required. Forced Bypass power saving mode is accessible using the I2C interface bus. The ISL9123 is capable of delivering up to 600mA of output current (VIN= 3.6V, VOUT= 1.8V) and provides excellent efficiency due to its adaptive frequency hysteretic control architecture. The ISL9123 is designed for stand-alone applications and supports a default output voltage at Power-On Reset (POR). After POR, the output voltage can be adjusted in the range of 0.4V to 5.375V by using the I2C interface bus. Specific default output voltages are available upon request. The ISL9123 requires only a single EIA 0603 size inductor and two external capacitors. Power supply solution size is minimized by a 1.8mm x 1.0mm WLCSP.