UCC1581

Micropower Voltage Mode PWM FEATURES Low 85µA Startup Current BLOCK DIAGRAM Low 300µA Operating Current Automatically Disabled Startup Preregulator Programmable Minimum Duty Cycle with Cycle Skipping Programmable Maximum Duty Cycle Output Current 1A Peak Source and Sink Programmable Soft Start Programmable Oscillator Frequency External Oscillator Synchronization Capability application INFO available UCC1581 UCC2581 UCC3581 Note: Pin Connection shown for 14-pin Package UDG-95011-1 DESCRIPTION The UCC3581 voltage mode pulse width modulator is designed to control low power isolated DC - DC converters in applications such as Subscriber Line Power (ISDN I.430). Primarily used for single switch forward and flyback converters, the UCC3581 features BiCMOS circuitry for low startup and operating current, while maintaining the ability to drive power MOSFETs at frequencies up to 100kHz. The UCC3581 oscillator allows the flexibility to program both the frequency and the maximum duty cycle with two resistors and a capacitor. A TTL level input is also provided to allow synchronization to an external frequency source. The UCC3581 includes programmable soft start circuitry, overcurrent detection, a 7.5V linear preregulator to control chip VDD during startup, and an on-board 4.0V logic supply. The UCC3581 provides functions to maximize light load efficiency that are not normally found in PWM controllers. A linear preregulator driver in conjunction with an ext...