The CS51021A/2A/3A/4A 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 startup current (75 mA) and high frequency operation capability, the CS51021A/2A/3A/4A family 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 V reference. The CS51021A and CS51023A feature bidirectional synchronization capability, while the CS51022A and CS51024A offer a sleep mode with 100 mA maximum IC current consumption. The CS51021A/2A/3A/4A family is available in a 16 lead narrow body SOIC package.