The XC9303 series is highly efficient, synchronous PWM, PWM/PFM switchable step-up & down DC/DC controller ICs. A versatile, large output current and high efficiency, step-up/down DC/DC controller can be realized using only basic external components - transistors, coil, diode, capacitors, and resistors for detecting voltages. High efficiency is obtained through the use of a synchronous rectification topology. The operation of the XC9303 series can be switched between PWM and PWM/PFM (auto switching) externally using the PWM pin. In PWM/PFM mode, the XC9303 automatically switches from PWM to PFM during light loads and high efficiencies can be achieved over a wide range of output loads conditions. Output noise can be easily reduced with PWM control since the frequency is fixed. Synchronous rectification control can be switched to non-synchronous by using external signals (MODE pin). High efficiency can be regulated at heavy loads when synchronous operation. The XC9303 has a 0.9V (2.0%) internal voltage supply and using externally connected components, output voltage can be set freely between 2.0V to 6.0V. With an internal 300kHz switching frequency smaller external components can be used. Soft-start time is internally set to 10msec and offers protection against in-rush currents when the power is switched on and prevents voltage overshoot.