Low power standby requirements are typically associatedwith battery-powered systems. Automotive systems,for example, commonly require power supplies tomaintain Output voltage regulation even under no-loadconditions—while drawing minimal quiescent current topreserve battery life. Rising energy costs, however, haveextended the need for low current standby operation toline-powered systems, such as small plugged-in appliancesfor home and business.
Automobile electronic systems place high demands ontoday’s DC/DC converters. They must be able to preciselyregulate an Output voltage in the face of wide temperatureand input voltage ranges—including load dump transientsin excess of 60V and cold crank voltage drops to 4V. Theconverter must also be able to minimize battery drain inalways-on systems by maintaining high effi ciency over abroad load current range. Similar demands are made bymany 48V nonisolated telecom applications, 40V FireWireperipherals and battery-powered applications with autoplug adaptors. The LT3437’s best in classperformancemeets all of these requirements in a small thermallyenhanced 3mm × 3mm DFN package.
A number of conventional solutions have been available forthe design of a DC/DC converter where the Output voltageis within the input voltage range—a common scenarioin Li-Ion battery-powered applications—but none werevery attractive until now. Conventional topologies, suchas SEPIC or boost followed by buck, have numerousdisadvantages, including low effi ciency, complex magnetics,polarity inversion and/or circuit complexity/cost. TheLTC®3785 buck-boost controller yields a simple, effi cient,low parts-count, single-converter solution that is easyto implement, thus avoiding the drawbacks associatedwith traditional solutions.
Video cable driver amplifi er Output stages traditionallyrequire a supply voltage of at least 6V in order to providethe required Output swing. This requirement is usuallymet with 5V supplies by adding a boost regulator or asmall local negative rail, say via the popular LT®1983-3.Such additional circuitry is unnecessary in typical 1VP-Pvideo connections, such as HD component video, if thecable driver amplifi ers simply offer near rail-to-rail Outputcapability when powered from 5V.
Automotive batteries, industrial power supplies, distributedsupplies and wall transformers are all sources ofwide-ranging high voltage inputs. The easiest way to stepdown these sources is with a high voltage monolithicstep-down regulator that can directly accept a wide inputrange and produce a well-regulated Output. The LT®3493accepts inputs from 3.6V to 36V and LT3481 acceptsinputs from 3.6V to 34V. Both provide excellent lineand load regulation and dynamic response. The LT3481offers a high effi ciency solution over a wide load range andkeeps the Output ripple low during Burst Mode® operationwhile the LT3493 provides a tiny solution with minimalexternal components. The LT3493 operates at 750kHzand the LT3481 has adjustable frequency from 300kHzto 2.8MHz. High frequency operation enables the use ofsmall, low cost inductors and ceramic capacitors.
Speed and accuracy don’t always go hand-in-handin DC/DC converter systems—that is, until now. TheLTC3811 is a dual Output, fi xed frequency current modeDC/DC switching regulator controller designed for one oftoday’s most demanding power supply applications: highcurrent, low voltage processor core supplies.
The LTC®3562 quad Output step-down regulator is designedfor multicore handheld microprocessor applications thatoperate from a single Li-Ion battery. Its four monolithic, higheffi ciency buck regulators support Intel’s mobile CPU P-Stateand C-State energy saving operating modes. The Outputvoltages are independently controllable via I2C, and eachOutput can be independently started and shut down. Designerscan choose from power saving pulse-skipping mode orBurst Mode® operation, or select low noise LDO mode. Thespace-saving LTC3562 is available in a 3mm × 3mm QFNpackage and requires few external components.
The LTC®3569 is a compact power solution for handhelddevices. Its tiny 3mm × 3mm QFN package includesthree buck regulators with individually programmableOutput voltages. One regulator supports load currentsup to 1200mA, while the other two support currents to600mA. Two regulators can be paralleled for increasedload capability. Each current-mode regulator is internallycompensated with excellent load and line regulation. Acomplete 2- or 3-Output solution requires a minimumof external passive components.
Industrial remote monitoring systems and keep-alivecircuits spend most of their time in standby mode. Manyof these systems also depend on battery power, so powersupply effi ciency in standby state is very important tomaximize battery life. The LT®8410/-1 high effi ciencyboost converter is ideal for these systems, requiringonly 8.5μA of quiescent current in standby mode. Thedevice integrates high value (12.4M/0.4M) Output feedbackresistors, signifi cantly reducing input current whenthe Output is in regulation with no load. Other featuresinclude an integrated 40V switch and Schottky diode,Output disconnect with current limit, built in soft-start,overvoltage protection and a wide input range, all in atiny 8-pin 2mm × 2mm DFN package.
Many system designers need an easy way to producea negative 3.3V power supply. In systems that alreadyhave a transformer, one option is to swap out the existingtransformer with one that has an additional secondarywinding. The problem with this solution is that manysystems now use transformers that are standard, offthe-shelf components, and most designers want toavoid replacing a standard, qualifi ed transformer with acustom version. An easier alternative is to produce thelow negative voltage rail by stepping down an existingnegative rail. For example, if the system already employsan off-the-shelf transformer with two secondary windingsto produce ±12V, and a –3.3V rail is needed, a negativebuck converter can produce the –3.3V Output from the–12V rail.
