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.
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