The above title is not happenstance and was arrived at afterconsiderable deliberation. As a linear IC manufacturer, it isour goal to encourage users to design and build switchingREGULATORs. A problem is that while everyone agrees thatworking switching REGULATORs are a good thing, everyonealso agrees that they are difficult to get working. SwitchingREGULATORs, with their high efficiency and small size, areincreasingly desirable as overall package sizes shrink.Unfortunately, switching REGULATORs are also one of themost difficult linear circuits to design. Mysterious modes,sudden, seemingly inexplicable failures, peculiar regulationcharacteristics and just plain explosions are commonoccurrences. Diodes conduct the wrong way. Things gethot that shouldn’t. Capacitors act like resistors, fusesdon’t blow and transistors do. The output is at ground, andthe ground terminal shows volts of noise.
The LT® 1529/LT1529-3.3/LT1529-5 are 3A low dropout
REGULATORs with micropower quiescent current and shutdown.
The devices are capable of supplying 3A of output
current with a dropout voltage of 0.6V. Designed for use
in battery-powered systems, the low quiescent current,
50mA operating and 16mA in shutdown, make them an
ideal choice. The quiescent current is well controlled it
does not rise in dropout as it does with many other low
dropout PNP REGULATORs.
Abstract: This document details the Lakewood (MAXREFDES7#) subsystem reference design, a 3.3V input, ±12V (±15V) output, isolated power supply. The Lakewood reference design includes a 3W primary-side transformer H-bridge driver for isolated supplies, and two wide input range and adjustable output low-dropout linear REGULATORs (LDOs). Test results and hardware files are included.
The LT®1943 is a highly integrated, 4-output regulatordesigned to power large TFT LCD panels. The LT1943employs switching REGULATORs—instead of linear REGULATORs—to minimize power dissipation and accommodate awide input voltage range. The wide input range, 4.5V to22V, allows it to accept a variety of power sources,including the commonly used 5V, 12V and 19V AC adaptors.
Multiple-voltage electronics systems often requirecomplex supply voltage tracking or sequencing, whichif not met, can result in system faults or even permanentfailures in the fi eld. The design diffi culties in meetingthese requirements are often compounded in distributedpowerarchitectures where point-of-load (POL) DC/DCconverters or linear REGULATORs are scattered across PCboard space, sometimes on different board planes. Theproblem is that power supply circuitry is often the lastcircuitry to be designed into the board, and it must beshoehorned into whatever little board real estate is left.Often, a simple, drop-in, fl exible solution is needed tomeet these requirements.
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.
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.
