The ADP3156 is a highly efficient synchronous buck switching regulator controller optimized for converting the 3.3 V or 5 V main supply into lower supply voltages required on the motherboards of Pentium III and other high performance processor systems. The ADP3156 uses a current mode, constant off-time architecture to drive two external N-channel MOSFETs at a programmable switching frequency that can be optimized for size and efficiency. It also uses a unique supplemental regulation technique called active voltage positioning to enhance load transient performance. Active voltage positioning results in a DC/DC converter that provides the best possible transient response using the minimum number of output capacitors and smallest footprint. Unlike voltage-mode and standard currentmode architectures, active voltage positioning adjusts the output voltage as a function of the load current so that it is always optimally positioned for a system transient. The ADP3156 provides accurate and reliable short circuit protection and adjustable current limiting. It also includes an integrated overvoltage crowbar function to protect the microprocessor from destruction in case the core supply exceeds the nominal programmed voltage by more than 15%.