LM27403 datasheet(13/49 Pages) TI

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LM27403

www.ti.com

SNVS896 A – AUGUST 2013 – REVISED SEPTEMBER 2013

OVERVIEW

APPLICATION AND ARCHITECTURE

The distributed power supply architecture, pervasive in myriad applications including communications

infrastructure equipment and computing systems, uses an intermediate bus and multiple downstream DC-DC

regulators dedicated and proximate to each “point-of-load.” The ASICs, FPGAs, and microprocessors that

comprise these loads have supply voltage requirements whose levels are decreasing on an absolute basis and

whose tolerance bands are decreasing on a percentage basis. The hallmarks of point-of-load (POL) DC-DC

regulators are efficiency, size, load transient response, and cost.

To this end, the LM27403 is a feature-rich, easy-to-use, synchronous PWM DC-DC step-down controller capable

of providing an ultrahigh current output for demanding, high power density POL applications. An input voltage

range of 3 V to 20 V is compatible with a wide range of intermediate bus system rails and battery chemistries;

especially 3.3-V, 5-V, and 12-V inputs. The output voltage is adjustable from 0.6 V to as high as 93% of the input

voltage, with better than ±1% feedback system regulation accuracy over the full junction temperature range. With

an accurate, adjustable and thermally-compensated inductor DCR based current limit setpoint, ferrite and

composite core inductors with low DCR and small footprint can be specified to maximize efficiency and reduce

power loss. High-current gate drivers with adaptive deadtime are used for the high-side and low-side MOSFETs

to provide further efficiency gains.

The LM27403 employs a voltage-mode control loop with output voltage remote sense, input voltage feedforward

modulation, and a high gain-bandwidth error amplifier to accurately regulate the output voltage over substantial

load, line, and temperature ranges. The switching frequency is programmable between 200 kHz and 1.2 MHz via

a resistor or an external synchronization signal. The LM27403 is available in a 4-mm × 4-mm, thermally-

enhanced, 24-lead WQFN PowerPad™ package. This device offers high levels of integration by including

MOSFET gate drivers, a low dropout (LDO) bias supply linear regulator, and comprehensive fault protection

features to enable highly-flexible, reliable, energy-efficient, and high power density regulator solutions.

Multiple

fault

conditions

are

accommodated,

including

overvoltage,

undervoltage,

overcurrent,

and

overtemperature. To improve overcurrent setpoint accuracy and enable easier filter inductor selection, the

LM27403 thermally compensates for the temperature coefficient (TC) of the inductor's winding resistance by

sensing the inductor temperature with an external NPN transistor configured as a thermal diode. The same

thermal diode also monitors the PCB temperature to initiate a thermal shutdown in the event that the sensed

temperature exceeds the programmed thermal shutdown setpoint.

DESIGN AND IMPLEMENTATION

To expedite and streamline the process of designing of a LM27403-based regulator for a given application, a

comprehensive LM27403 design tool is available for download. This is complimented by the availability of two

LM27403 evaluation modules (EVMs) as well as numerous LM27403 designs populated in TI's PowerLab™

reference design library. In addition, five designs are provided in the DESIGN EXAMPLES section of this

datasheet. The LM27403 is also Webench®-enabled.

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