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