uc3844bn

high performance
current mode controllers

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the uc3844b, uc3845b series are high performance fixed frequency
current mode controllers. they are specifically designed for off−line
and dc−dc converter applications offering the designer a cost−effective
solution with minimal external components. these integrated circuits
feature an oscillator, a temperature compensated reference, high gain
error amplifier, current sensing comparator, and a high current totem pole
output ideally suited for driving a power mosfet.
also included are protective features consisting of input and reference
undervoltage lockouts each with hysteresis, cycle−by−cycle current
limiting, a latch for single pulse metering, and a flip−flop which blanks
the output off every other oscillator cycle, allowing output deadtimes to
be programmed from 50% to 70%.
these devices are available in an 8−pin dual−in−line and surface
mount (soic−8) plastic package as well as the 14−pin plastic surface
mount (soic−14). the soic−14 package has separate power and
ground pins for the totem pole output stage.
the ucx844b has uvlo thresholds of 16 v (on) and 10 v (off),
ideally suited for off−line converters. the ucx845b is tailored for
lower voltage applications having uvlo thresholds of 8.5 v (on) and
7.6 v (off).
features
• trimmed oscillator for precise frequency control
• oscillator frequency guaranteed at 250 khz
• current mode operation to 500 khz output switching frequency
• output deadtime adjustable from 50% to 70%
• automatic feed forward compensation
• latching pwm for cycle−by−cycle current limiting
• internally trimmed reference with undervoltage lockout
• high current totem pole output
• undervoltage lockout with hysteresis
• low startup and operating current
• pb−free packages are available