Current Mode PWM  Control Circuit with  50% Max Duty Cycle

The CS3844/45 provides all the necessary features to implement off–line fixed frequency current–mode control with a minimum number of external components.
The CS3844 family incorporates a new precision temperature–controlled oscillator to minimize variations in frequency. An internal toggle flip–flop, which blanks the output every other clock cycle, limits the duty–cycle range to less than 50%. An undervoltage lockout ensures that VREF is stabilized before the output stage is enabled. In the CS2844/CS3844 turn on occurs at 16 V and turn off at 10 V. In the CS2845/CS3845 turn on is at 8.4 V and turn off at 7.6 V.

Features
• Optimized for Off–Line Control
• Temp. Compensated Oscillator
• 50% Max Duty–Cycle Clamp
• VREF Stabilized Before Output Stage Is Enabled
• Low Start–Up Current
• Pulse–By–Pulse Current Limiting
• Improved Undervoltage Lockout
• Double Pulse Suppression
• 1.0% Trimmed Bandgap Reference
• High Current Totem Pole Output