To this day, Power over Ethernet (PoE) continues to gainpopularity in today’s networking world. The 12.95Wdelivered to the Powered Device (PD) input supplied bythe Power Sourcing Equipment (PSE) is a universal supply.Each PD provides its own DC/DC conversion from anominal 48V supply, thus eliminating the need for a correctvoltage wall adapter. However, higher power devicescan not take advantage of standard PoE because of itspower limitations, and must rely on a large wall adapteras their primary supply. The new LTC4268-1 breaks thispower barrier by allowing for power of up to 35W for suchpower-hungry 2-pair PoE applications. The LTC4268-1provides a complete solution by integrating a high powerPD interface control with an isolated fl yback controller.
Many telecommunications and computing applicationsneed high effi ciency step-down DC/DC converters thatcan operate from a very low input voltage. The highoutput power synchronous controller LT3740 is idealfor these applications, converting input supplies rangingfrom 2.2V to 22V to outputs as low as 0.8V with loadcurrents from 2A to 20A. Applications include distributedpower systems, point-of-load regulation and conversionof logic 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.
Alkaline batteries are convenient because they’re easy tofi nd and relatively inexpensive, making them the powersource of choice for portable instruments and devicesused for outdoor recreation. Their long shelf life alsomakes them an excellent choice for emergency equipmentthat may see infrequent use but must be ready to go on amoment’s notice. It is important that the DC/DC convertersin portable devices operate over the widest possiblebattery voltage range to extend battery run time, and thussave the user from frequent battery replacement.
Avalanche photo diode (APD) receiver modules arewidely used in fi ber optic communication systems. AnAPD module contains the APD and a signal conditioningamplifi er, but is not completely self contained. It stillrequires signifi cant support circuitry including a highvoltage, low noise power supply and a precision currentmonitor to indicate the signal strength. The challenge issqueezing this support circuitry into applications withlimited board space. The LT®3482 addresses this challengeby integrating a monolithic DC/DC step-up converter andan accurate current monitor. The LT3482 can supportup to a 90V APD bias voltage, and the current monitorprovides better than 10% accuracy over four decades ofdynamic range (250nA to 2.5mA).
Advances in low power electronics now allow placementof battery-powered sensors and other devices in locationsfar from the power grid. Ideally, for true grid independence,the batteries should not need replacement, but instead berecharged using locally available renewable energy, suchas solar power. This Design Note shows how to producea compact battery charger that operates from a small2-cell solar panel. A unique feature of this design is thatthe DC/DC converter uses power point control to extractmaximum power from the solar panel.
Linear Technology’s DC/DC step-down μModule®regulators are complete switchmode power supplies in asurface-mount package. They include the DC/DC controller,inductor, power switches and supporting circuitry.These highly integrated regulators also provide an easysolution for applications that require negative outputvoltages. In other words, these products can operate asinverting buck-boost regulators. As a result, the lowestpotential in the circuit is not the standard 0V, but –VOUT,which must be tied to the μModule regulator’s GND. Allsignals are now referred to –VOUT.
The LTC®3610 is a high power monolithic synchronousstep-down DC/DC regulator that can deliver up to 12Aof continuous output current from a 4V to 24V (28Vmaximum) input supply. It is a member of a high currentmonolithic regulator family (see Table 1) that featuresintegrated low RDS(ON) N-channel top and bottomMOSFETs. This results in a high effi ciency and highpower density solution with few external components.This regulator family uses a constant on-time valleycurrent mode architecture that is capable of operatingat very low duty cycles at high frequency and with veryfast transient response. All are available in low profi le(0.9mm max) QFN packages.
High voltage buck DC/DC controllers such as the LTC3890(dual output) and LTC3891 (single output) are popular inautomotive applications due to their extremely wide 4V to60V input voltage range, eliminating the need for a snubberand voltage suppression circuitry. These controllersare also well suited for 48V telecom applications whereno galvanic isolation is required.
A recent trend in the design of portable devices has beento use ceramic capacitors to filter DC/DC converter inputs.Ceramic capacitors are often chosen because of theirsmall size, low equivalent series resistance (ESR) and highRMS current capability. Also, recently, designers havebeen looking to ceramic capacitors due to shortages oftantalum capacitors.
