The MC33364 series are variable frequency SMPS controllers that operate in the critical conduction mode. They are optimized for low power, high density power supplies requiring minimum board area, reduced component count, and low power dissipation. Each narrow body SOIC package provides a small footprint. Integration of the high voltage startup saves approximately 0.7 W of power compared to resistor bootstrapped circuits. Each MC33364 features an onboard reference, UVLO function, a watchdog timer to initiate output switching, a zero current detector to ensure critical conduction operation, a current sensing comparator, leading edge blanking, and a CMOS driver. Protection features include the ability to shut down switching, and cyclebycycle current limiting. The MC33364D1 is available in a surface mount SO8 package. It has an internal 126 kHz frequency clamp. For loads which have a low power operating condition, the frequency clamp limits the maximum operating frequency, preventing excessive switching losses and EMI radiation. The MC33364D2 is available in the SO8 package without an internal frequency clamp.