The SC4809A/B/C is a 10 pin BICMOS primary side current mode controller for use in Isolated DC-DC and off-line switching power supplies. It is a highly integrated solution, requiring few external components. It features a high frequency of operation, accurately programmable maximum duty cycle, current mode control, line voltage monitoring, supply UVLO, low start-up current, and programmable soft start with user accessible reference. It operates in a fixed frequency, highly desirable for Telecom applications. Features a separate sync pin which simplifies synchronization to an external clock. Feeding the oscillator of one device to the sync of another forces biphase operation which reduces input ripple and filter size.