Linear Design Features - LTJournal-V20N3-02-df-LTM4611 Jason Sekanina Technical Manual User Guide

POL µModule DC/DC Converter Operates from Inputs Down to 1.5V, Delivering Up to 15A Output, Without an Auxiliary Bias Supply Jason Sekanina and Alan Chern

The LTM4611 is a low profile µModule step-down switch mode DC/DC converter in a compact 15mm × 15mm × 4.32mm LGA surface mount package. The switching controller, MOSFETs, inductor and support components are housed in the package, so design is reduced to selecting a few external components. The LTM4611 operates from an input voltage of 1.5V to 5.5V (6V, absolute maximum), making it suitable for a variety of power architectures—particularly data storage and RAID (redundant array of independent disks) systems, ATCA (advanced telecommunications computing architecture) and networking cards—where one or several commonly bussed voltages are 5V, 3.3V, 2.8V, and/or 2.5V. While it is uncommon to see bus voltages leave the bus voltage compromised, but could convert the 5V rail to a distributed lower than 2.5V due to the distribution still above 1.5V. The LTM4611’s abil- 1.5V copper plane, while another LTM4611 losses (voltage drops) associated with ity to deliver full power from as low as could efficiently convert the 1.5V bus relatively high bus currents, the ability 1.5V input allows it to be considered for voltage to 1.2V at the POL. The resulting of the LTM®4611 to deliver full power to mission-critical medical and industrial total solution size on the motherboard its load from a 1.5V input is particularly instruments that have the highest stan- could be quite compelling, while eliminat- advantageous in applications where load dards for uptime and bus-sag ride-through ing the need to route 5V potential to an voltage(s) must be precisely regulated capability. Precision-regulated power can entire section of the PCB. The option to even as momentary or sustained electri- even be provided by the LTM4611 to its minimize the number of layers of cop- cal events induce input-bus line-sag. load during so-called “dying-gasps”—sud- per in the manufacture of the PCB has Transient events on the system bus can den, unexpected loss of system power, potential for cost and material savings, occur normally due to the operation of such as those monitored by utility smart and associated benefits to PCB yield in motors, transducers, defibrillators or an meters—where it is highly desirable to mass-production and PCB reliability. uptick in microprocessor activity. Fault be able to operate from the decaying

BRAINS AND BRAWN

events on a system’s distributed bus may voltage provided by backup-batteries or

The muscle behind the LTM4611 is a

supercapacitors for as long as possible.

buck-converter topology that steps down There is another advantage in the its input voltage to deliver as low as 0.8V, LTM4611’s ability to operate from as low up to 15A continuous, to its output. A

Scan This

as 1.5V: as the number of rails increases voltage drop less than 0.3V from input-to- in today’s power system, so are the output and at 15A load is achievable, with

SCAN THIS CODE WITH

YOUR SMART PHONE number of layers of copper in printed proper selection of input-power-source

This particular code, like its (dynamic characteristic and transient load

circuit boards (PCBs) required to route

clone on the cover, links to the

(distribute) the power effectively to the response) and local bypass capacitance.

mobile version of the LTM4611 web page at

m.linear.com/4611. Most smart phones support load. Consider a hypothetical example: it

SELF-GENERATED BIAS SUPPLY

QR Code scanning using their built-in cameras. can be difficult to impossible to route a

Another noteworthy feature is that the

Some phones may require that you download

distributed 5V rail to both 5V-to-1.5V and

a QR Code scanner/reader application. Look LTM4611 does not require an auxiliary bias

5V-to-1.2V DC/DC converters without

through this article for a few more codes that supply to power its internal control IC or link to informative videos. increasing the number of layers of cop-

MOSFET-drive circuitry; it generates its

per in the PCB. Alternatively, one LTM4611

own low power bias from the input-source

12 | October 2010 : LT Journal of Analog Innovation