LM5027 Datasheet, PDF (1/26 Pages) National Semiconductor (TI) – Voltage Mode Active Clamp Controller

LM5027
August 18, 2009
Voltage Mode Active Clamp Controller
General Description
The LM5027 pulse-width modulation (PWM) controller con-
tains all of the features necessary to implement power con-
verters 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 out-
puts are provided: the main power switch control (OUTA), the
active clamp switch control (OUTB), and secondary side syn-
chronous rectifier control (OUTSR). The timing between the
control outputs is adjustable with external resistors that pro-
gram 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 LM5027 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 ther-
mal shutdown.
Features
■ ^{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}
■ ^{Programmable 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}
Packages
■ ^eTSSOP-20
Typical Application Circuit
Simplified Active Clamp Converter
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