The MC33364 series are variable frequency SMPS controllers that operate in the critical conduction mode. They are optimized for high density power supplies requiring minimum board area, reduced component count, and low power dissipation. Integration of the high voltage startup saves approximately 0.7 W of power compared to the value of the resistor bootstrapped circuits. Each MC33364 features an on--board 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, a CMOS driver and cycle--by--cycle current limiting. The MC33364D1 has an internal 126 kHz frequency clamp. The MC33364D2 is available without an internal frequency clamp. The MC33364D has an internal 126 kHz frequency clamp which is pinned out, so that the designer can adjust the clamp frequency by connecting appropriate values of resistance.