The makers of handheld medical, industrial and consumerdevices use a wide variety of high resolution, small tomedium sized color TFT LCD displays. The power supplydesigners for these displays must contend with shrinkingboard area, tight schedules, and variations in displaytypes and feature requirements. The LTC®3524 simplifi esthe designer’s job by combining a versatile, easily programmed,TFT LCD bias supply and white LED backlightdriver in a low profi le 4mm × 4mm QFN package.
Piezoelectric motors are used in digital cameras for autofocus,zooming and optical image stabilization. Theyare relatively small, lightweight and effi cient, but theyalso require a complicated driving scheme. Traditionally,this challenge has been met with the use ofseparatecircuits, including a step-up converter and an oversizedgeneric full-bridge drive IC. The resulting high componentcount and large board space are especially problematicin the design of cameras for ever shrinking cell phones.The LT®3572 solves these problems by combining astep-up regulator and a dual full-bridge driver in a 4mm× 4mm QFN package. Figure 1 shows a typical LT3572Piezo motor drive circuit. A step-up converter is usedto generate 30V from a low voltage power source suchas a Li-Ion battery or any input power source within thepart’s wide input voltage range of 2.7V to 10V. The highoutput voltage of the step-up converter, adjustable upto 40V, is available for the drivers at the VOUT pin. Thedrivers operate in a full-bridge fashion, where the OUTAand OUTB pins are the same polarity as the PWMA andPWMB pins, respectively, and the OUTA and OUTB pinsare inverted from PWMA and PWMB, respectively. Thestep-up converter and both Piezo drivers have their ownshutdown control. Figure 2 shows a typical layout
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.
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.
As environmental concerns over traditional lighting increaseand the price of LEDs decreases, high power LEDsare fast becoming a popular lighting solution for offl ineapplications. In order to meet the requirements of offl inelighting—such as high power factor, high effi ciency, isolationand TRIAC dimmer compatibility—prior LED driversused many external discrete components, resulting incumbersome solutions. The LT®3799 solves complexity,space and performance problems by integrating all therequired functions for offl ine LED lighting.
Once relegated to the hinterlands of low cost indicatorlights, the LED is again in the spotlight of the lightingworld. LED lighting is now ubiquitous, from car headlightsto USB-powered lava lamps. Car headlights exemplifyapplications that capitalize on the LED’s clear advantages—unwavering high quality light output, tough-assteelrobustness, inherent high effi ciency—while a USBlava lamp exemplifi es applications where only LEDs work.Despite these clear advantages, their requirement forregulated voltage and current make LED driver circuitsmore complex than the venerable light bulb, but some newdevices are closing the gap. For instance, the LTM®8040μModule™ LED driver integrates all the driver circuitryinto a single package, allowing designers to refocus theirtime and effort on the details of lighting design criticalto a product’s success.
An essential component of a noise-free audio device isa clean power supply, but few switching regulators canoperate at high efficiency while keeping the switchingfrequency out of the audio band. The LTC®3620 fills thisvoid. It is a high efficiency 15mA buck regulator with aprogrammable minimum switching frequency, making itpossible to virtually eliminate audible switching noise. Theinternal synchronous switches and low quiescent currentof this buck regulator provide the ability to maintain highefficiency, while its small footprint makes it ideal for tiny,low power audio applications.
Avalanche photodiodes (APDs) are widely utilized in laserbased fiberoptic systems to convert optical data intoelectrical form. The APD is usually packaged with a signalconditioning amplifier in a small module. An APD receivermodule and attendant circuitry appears in Figure 1. TheAPD module (figure right) contains the APD and a transimpedance(e.g., current-to-voltage) amplifier. An opticalport permits interfacing fiberoptic cable to the APD’sphotosensitive portion. The module’s compact constructionfacilitates a direct, low loss connection between theAPD and the amplifier, necessary because of the extremelyhigh speed data rates involved
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.
