The LM5027A is a functional variant of the LM5027 active clamp PWM controller. The functional difference of the LM5027A is that the maximum duty cycle of the LM5027A is decreased from 91% to 71%. In addition, the oscillator timing equation has been modified.

The LM5027A pulse-width modulation (PWM) controller contains all of the features necessary to implement power converters utilizing the Active Clamp / Reset technique. With the active clamp technique, higher efficiencies and greater power densities can be realized compared to conventional catch winding or RDC clamp / reset techniques. Three control outputs are provided: the main power switch control (OUTA), the active clamp switch control (OUTB), and secondary side synchronous rectifier control (OUTSR). The timing between the control outputs is adjustable with external resistors that program internal precision timers. This controller is designed for high-speed operation including an oscillator frequency range up to 1 MHz and total PWM propagation delays less than 50 ns. The LM5027A includes a high-voltage startup regulator with a maximum input voltage rating of 105V. Additional features include Line Under Voltage Lockout (UVLO), separate soft-start of main and synchronous rectifier outputs, a timer for hiccup mode current limiting, a precision reference, and thermal shutdown.

• Voltage-Mode Control
• Line Feed-Forward PWM Ramp
• Internal 105V Rated Start-Up Bias Regulator
• Programmable Line Under-Voltage Lockout (UVLO) with Adjustable Hysteresis
• Versatile Dual Mode Over-Current Protection
• Programmable Volt-Second Limiter and Soft-Start
• Programmable Synchronous Rectifier Soft-Start and Stop
• Precise 500mV Over-Current Comparator
• Current Sense Leading Edge Blanking
• Programmable Oscillator With 1 MHz Maximum Frequency and Synchronization Capability
• Precision 5V Reference
• Programmable Time Delays Between Outputs
• A 70% Maximum Duty Cycle