National Semiconductor Corp.'s LM5119, a
high voltage, dual-channel, dual-phase, synchronous buck controller with
emulated current-mode (ECM) control
enables regulation of single or dual high-current voltages directly from
inputs as high as 65V, simplifying high voltage dc-dc conversion and reducing
PCB footprint by up to 50 percent versus alternative solutions requiring two
conversion stages. The LM5119 features a unique combination of high
performance, flexibility and ease-of-use for demanding telecommunication,
automotive and industrial control applications that require accurate voltage
regulation. The device expands National's portfolio of high voltage synchronous buck controllers to address higher load currents.
Today's telecommunication, automotive and
industrial control applications must regulate low output voltages at increasing
load currents from a high input voltage that can change widely while still
meeting stringent PCB space and efficiency requirements. Traditional
approaches require two dc-dc conversion stages: one to regulate an intermediate
bus voltage of approximately 9V to 12V and a second to regulate the specific
load voltages that can be as low as 1V and can require currents in excess of 20
amperes. National's LM5119 enables direct regulation of two output
voltages from an input, eliminating the need for an intermediate bus conversion
stage that limits efficiency and requires up to twice the number of
components. National's proprietary ECM control technology enables precise
control of very small duty cycles necessary in high voltage applications, which
allows accurate regulation of dc output voltages with excellent transient
response. For high-current output requirements,
the two outputs can be connected in parallel to power loads up to 40A with
interleaved switching that minimizes input and output capacitance.
LM5119 features a wide operating voltage range of 5.5 to 65 and a 0.8V, 1.5
percent reference enables accurate regulation of load voltages from 0.8V up to
90 percent of the input voltage. The operating frequency is user-programmable
from 50 kHz up to 750 kHz and can be synchronized to an external clock
signal. Diode emulation mode (DEM) enables discontinuous inductor current
operation at light load conditions for improved efficiency. This mode
allows controlled start-up into a pre-biased load by preventing current flow
into the synchronous MOSFET. A high voltage bias regulator with automatic
switch-over to external bias further improves efficiency. Additional
features include thermal shutdown, cycle-by-cycle and hiccup mode current limit
and adjustable line under-voltage lockout. The wide Vin range, multi-phase
operation, programmable soft-start, input UVLO and diode emulation mode
together enhance the system designer's flexibility and control of all
The LM5119 is
offered in a 5 by 5 mm 32-pin LLP package. For those designs
that require an input range from 4.5V to 42V, the LM25119 is
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