The CS51021 Fixed Frequency PWM Current Mode Controller family provides all necessary features required for ac-dc or dc-dc primary side control. Several features are included eliminating the additional components needed to implement them externally. In addition to low start-up current (75 µA)and high frequency operation capability, the Enhanced Current Mode PWM Controller includes overvoltage and undervoltage monitoring, externally programmable dual threshold overcurrent protection, current sense leading edge blanking, current slope compensation, accurate duty cycle control and an externally available 5.0 volt reference. The CS51021A features bidirectional synchronization capability, while the CS51022A offers a sleep mode with 100 µA maximum IC current consumption. The CS51021A/2A Enhanced Current Mode PWM Controllers are available in a SOIC-16 or TSSOP-16 lead package.