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Power Application Notes
This application note describes the unique operating characteristics of the LT1005 and describes a number of useful applications which take advantage of the regulator's ability to control the output with a logic control signal.
This application note describes a number of enhancement circuit techniques used with existing 3-terminal regulators which extend current capability, limit power dissipation, provide high voltage output, operate from 110VAC or 220VAC without the need to switch transformer windings, and many other usefu application ideas.
A variety of approaches for power conditioning batteries is given. Switching and linear regulators and converters are shown, with attention to efficiency and low power operation. 14 circuits are presented with performance data.
This note covers the considerations for designing precision linear circuits which must operate from a single 5V supply. Applications include various transducer signal conditioners, instrumentation amplifiers, controllers and isolated data converters.
1.5V powered circuits for complex linear functions are detailed. Designs include a V/F converter, a 10-bit A/D, sample-hold amplifiers, a switching regulator and other circuits. Also included is a section of component considerations for 1.5V powered linear circuits.
This design manual is an extensive discussion of all standard switching configurations for the LT1070; including buck, boost, flyback, forward, inverting and "Cuk." The manual includes comprehensive information on the LT1070, the external components used with it, and complete formulas for calculating component values.
Subtitled "A Gentle Guide for the Trepidatious," this is a tutorial on switching regulator design. The text assumes no switching regulator design experience, contains no equations, and requires no inductor construction to build the circuits described. Designs detailed include flyback, isolated telecom, off-line, and others. Appended sections cover component considerations, measurement techniques and steps involved in developing a working circuit.
This note examines a wide range of DC/DC converter applications. Single inductor, transformer, and switched-capacitor converter designs are shown. Special topics like low noise, high efficiency, low quiescent current, high voltage, and wide-input voltage range converters are covered. Appended sections explain some fundamental properties of different types of converters.
Switching regulators are of universal interest. Linear Technology has made a major effort to address this topic. A catalog of circuits has been compiled so that a design engineer can swiftly determine which converter type is best. This catalog serves as a visual index to be browsed through for a specific or general interest.
Subtitled "Some Affable Analogs for Digital Devotees," discusses a number of analog circuits useful in predominantly digital systems. VPP generators for flash memories receive extensive treatment. Other examples include a current loop transmitter, dropout detectors, power management circuits, and clocks.
Presents circuit techniques permitting high efficiency to be obtained with linear regulation. Particular attention is given to the problem of maintaining high efficiency with widely varying inputs, outputs and loading. Appendix sections review component characteristics and measurement methods.
Discusses the LT1074, an easily applied step-down regulator IC. Basic concepts and circuits are described along with more sophisticated applications. Six appended sections cover LT1074 circuitry detail, inductor and discrete component selection, current measuring techniques, efficiency considerations and other topics.
Safe, fast charging of NiCad batteries is attractive in many applications. This note details simple, thermally-based fast charge circuitry for NiCads. Performance data is summarized and compared to other charging methods.
This note explores the causes of the large resonating current spikes on the leading edge of the switch current waveform. These anomalies are exacerbated in very high voltage designs.
This note discusses the use of the LT1074 and LT1076 high efficiency switching regulators. These regulators are specifically designed for ease of use. This application note is intended to eliminate the most common errors that customers make when using switching regulators as well as offering insight into the inner workings of switching designs. There is an entirely new treatment of inductor design based upon simple mathematical formulas that yield direct results. There are extensive tutorial sections devoted to the care and feeding of the Positive Step- Down (Buck) Converter, the Tapped Inductor Buck Converter, the Positive-to-Negative Converter and the Negative Boost Converter. Additionally, many troubleshooting hints are included as well as oscilloscope techniques, soft-start architectures, and micropower shutdown and EMI suppression methods.
Efficiency varies for different DC/DC converters. This application note compares the efficiency characteristics of some of the more popular types. Step-up, step-down, flyback, negative-to-positive, and positive-to-negative are shown. Appended sections discuss how to select the proper aluminum electrolytic capacitor and explain power switch and output diode loss calculations.
Current generation portable computers and instruments utilize backlit liquid crystal displays. The back light requires a highly efficient, high voltage AC source as well as other supply circuitry. AN49 details these circuits and also includes sections on efficiency measurements and instrumentation considerations. A separate section discusses physical and layout considerations for the display.
Notebook and palmtop systems need a number of voltages developed from a battery. Competitive solutions require small size, high efficiency and light weight. This publication includes circuits for high efficiency 5V and 3.3V switching and linear regulators, back light display drivers and battery chargers. All the circuits are specifically tailored for the requirements outlined above.
This application note consolidates the circuits from the first few years of Linear Technology magazine into one publication. Presented in the note are a variety of circuits ranging from a 50W high efficiency (&90%) switching regulator to steep roll-off filter circuits with low distortion to 12-bit differential temperature measurement systems.
This application note describes the operation of high-side Nchannel MOSFET switch drivers designed specifically for operation in battery-powered equipment, such as notebook and palmtop computers and portable medical instruments. A selection guide simplifies the proper choice of MOSFET and driver for a particular high-side switch application. Circuits to drive and protect load impedances ranging from large inductors to large capacitors are described and a section on surface mount and copper clad shunts is included.
This application note discusses the use of the LTC1147, LTC1148, and LTC1149 ultra high efficiency switching regulators in a wide variety of applications. These controllers feature a current-mode architecture which includes an automatic low current operating mode called Burst ModeTM operation, making greater than 90% efficiencies possible at output currents as low as 10mA. This feature maximizes battery life while a product is in sleep or standby modes. In addition, the LTC1148 and LTC1149 are synchronous switching regulators which achieve high efficiency conversion from 10mA to 10A.
This publication details several LCD backlight circuits which feature 92% efficiency. Other benefits include low voltage operation, synchronizing capability, higher output power for color displays, and extended dimming range. Extensive coverage of practical issues includes layout problems, multi-lamp displays, safety and reliability concerns and efficiency and photometric measurements. Also included is a review of circuits which did not work along with appropriate commentary.
Many popular microprocessors operate from 3.3V supplies, yet they are used in systems where the predominate source of power is 5V. AN58 presents a collection of both linear and switching regulator solutions for conversion of 5V to 3.3V at currents ranging from 100mA to 20A. Applications information and a comparison of various bypass capacitor types is included. Most of the designs can be easily modified for other intermediate voltages such as 3.45V, 3.7V, and 4.1V.
This note covers operation and applications of the LT1300 and LT1301 high efficiency micropower step-up DC/DC converter ICs. Internal operation of the ICs is described in detail. A variety of applications are presented, ranging from straightforward 2-cell to 5V converters and 5V to 12V converters to exotic transducerbased circuits such as flame detectors and CCFL drivers. Converters from both 2-cell and 4-cell inputs are included. Operating hours at various load currents are presented and relative merits of different battery types are discussed.
Most portable systems have expansion sockets conforming to the standards set by the Personal Computer Memory Card International Association (PCMCIA). This standard requires the host to perform an unusual amount of switching on both the VCC and VPP voltage lines. Card designers face difficult power management and DC/DC conversion issues of their own. Board real estate and component height are at a premium making design difficult and component selection critical. This application note discusses in detail both the host and card designer issues and highlights several new products designed specifically for these applications.
This collection of circuits was worked out between June 1991 and July of 1994. Most were designed at customer request or are derivatives of such efforts. Types of circuits include power converters, transducer signal conditioners, amplifiers and signal generators. Specific circuits include low noise amplifiers, high power single cell DC/DC converters, portable high accuracy barometers, a 10mHz 1% accuracy RMS/DC converter, and random noise generators. Appended sections cover noise theory and present a historical perspective of wideband amplifiers.
This application note describes the design of both linear and switching regulators which provide power for 90MHz Pentium(r) processors. The circuits are intended to comply with Intel's modular power supply specification and provide sufficient power for cache RAM and chip sets in addition to the CPU. They are also capable of providing the additional power required by an upgrade "overdrive" processor.
Application Note 64 details characteristics of various battery types and appropriate charging management schemes. The LTC1325 battery management IC is highlighted along with information for applying it to any type battery. Techniques and circuitry for conditioning, charging and monitoring NiCd, NiMH, Li-Ion and Lead-Acid batteries are presented.
This publication, LTC's fourth effort devoted to LCD backlighting in as many years, treats the subject comprehensively. The text considers lamps, display and layout induced losses, circuitry, efficiency related issues, optimization and measurement techniques. Twelve appended sections cover lamp types, mechanical design, electrical and photometric measurement, layout, circuitry and related topics.
Application Note 66 is a compendium of "power circuits" from the first five years of Linear Technology. This application note contains circuits that can power most any system you can imagine, from desktop computer systems to micropower systems for portable and handheld equipment. Also included here are circuits that provide 300W or more of power factor corrected DC from a universal input. Battery chargers are included, some that charge several battery types, some that are optimized to charge a single type. MOSFET drivers, high side switches and H-bridge driver circuits are also included, as is an article on simple thermal analysis.
The ever-growing popularity of portable equipment in recent years has pushed battery technologists to search for battery types that store more energy in a smaller volume, weigh less and are safer. Also, the power source selection for charging the batteries has diversified. For example, a notebook computer can be connected to a car battery, a power adapter, a docking station or even to solar cells. The variety of input voltages, coupled with the need for high efficiency and the need for accurate constant voltage and constant current, as in the case of Li-Ion batteries (see below), have led to the introduction of a switching type constant-voltage, constant-current battery charger IC, the LT&1510.
AN69 describes considerations for linear regulators based on the LT1575 UltraFastTM Linear Regulator controller. The LT1575 drives an external MOSFET pass transistor as an overdriven source follower. This configuration results in an extremely high speed regulation loop which minimizes the need for output capacitors. Target applications are state of the art microprocessor core supplies which exhibit large, high speed load transients while having very tight supply voltage tolerance requirements. The application note shows numerous examples of circuit implementations and offers detailed discussions of design considerations.
This publication details circuitry and applications considerations for the LT1533 low noise switching regulator. Eleven DC/DC converter circuits are presented, some offering &100&V output noise in a 100MHz bandwidth. Tutorial sections detail low noise DC/DC design, measurement, probing and layout techniques, and magnetics selection.
This application note contains detailed design information to allow the reader to craft switching regulators using the LT1339 high power synchronous DC/DC converter. The note provides expanded pin descriptions for the LT1339 as well as easy-to-use graphical tools for the design of high power synchronous buck and boost converters. The manual includes extensive information on the LT1339 and the external components used with it along with formulas and/or graphics to calculate component values.
This publication includes designs for data converters and signal conditioners, transducer circuits, crystal oscillators and power converters. Wideband and micropower circuitry receive special attention. Tutorials on micropower design techniques and parasitic effects of test equipment are included.
Loop compensation is an uncomfortable subject for many engineers. Experienced power supply designers know that optimum loop compensation is necessary to get the best performance from their power supplies. This application note discusses power supply loop compensation utilizing the features provided by the OPTILOOPTM architecture. Loop compensation basics are presented and simple equations are given for frequency response approximations. Typical transient response requirements for the system supply and CPU supply, used in notebook computers, are discussed. Output voltage transient response waveforms and Bode plots are shown for both optimized and nonoptimized control loops as well as for circuits with optimized loops using different output capacitors. Although this publication focuses on circuits using the LTC1628, LTC1735 and LTC1736, the information applies to all regulators equipped with OPTI-LOOP architecture.
This application note addresses the following questions. How much do I gain by using a PolyPhaseTM architecture? How many phases do I need for my application? How do I design a PolyPhase converter? The design example of an LTC1629-based, 6-phase 90A power converter is presented. The mathematical equations and graphical curves for calculating the ripple currents are included.
It has become desirable to fashion laptop computers with large area screens, leaving little room for the display's backlight inverter electronics. Miniaturization limitations of high voltage magnetic transformers impose limits on achievable space reduction. Another voltage step-up technology, piezoelectric transformers, permits the desired size reduction and provides additional benefits. This publication describes practical piezoceramic transformers and support circuitry. Ancillary benefits of the piezoelectric approach are also described. Appended sections detail transformer operation and feedback loop considerations.
In an increasing trend, telecommunications, networking, audio and instrumentation require low noise power supplies. In particular, there is interest in low noise, low dropout linear regulators (LDO). Establishing and specifying LDO dropout performance is relatively easy to do. Verifying that a regulator meets dropout specification is similarly straightforward. Accomplishing the same missions for noise and noise testing is considerably more involved. The noise bandwidth of interest must be called out, along with operating conditions. Low noise performance is affected by changes in operating conditions can cause unwelcome surprises. Because of this, LDO noise must be quoted under specified operating and bandwidth conditions to be meaningful. Failure to observe this precaution results in misleading data and erroneous conclusions. This Application Note suggests a noise testing method, details its implementation and presents results.
Application Note 84 is a collection of "power circuits" from the years 1996 through 1998 as seen in the pages of Linear Technology magazine. This Application Note collects circuits that can output tens of amps to circuits that can operate a handheld device for several years. In addition to a wide variety of traditional power supply circuits (Buck, Boost, Inverting, Flyback, Linear Regulators, etc.) we include circuits for charging batteries, several Power Management circuits as well as circuits that highlight a very low noise switching regulator.
Telecommunication, satellite links and set-top boxes all require tuning a high frequency oscillation. The actual tuning element, a varactor diode, requires high voltage bias for operation. The high voltage bias must be free of noise to prevent unwanted oscillator outputs. This publication details a method for generating noise free high voltage from low voltage inputs using switching regulators. Spurious oscillator outputs are below -90dBc. Suggested circuit and layout information is included. Appendices cover varactor diode theory and performance verification techniques.
When it comes to input filtering, ceramic capacitors are a great choice. They offer high ripple current rating and low ESR and ESL. Also, ceramic capacitors are not very sensitive to over voltage and can be used without derating the operating voltage. However, designers must be aware of a potential overvoltage condition that is generated when input voltage is applied abruptly. After applying an input voltage step, typical input filter circuits with ceramic capacitors can generate voltage transients twice as high as the input voltage. Application Note 88 describes how to efficiently use ceramic capacitors for input filters and how to avoid potential problems due to input voltage transients.
This application note presents circuitry for maintaining 0.01&C temperature control of fiber optic lasers over wide ambient range variations. The circuitry also features high efficiency power delivery, compact size and low noise. Detailed descriptions of circuitry and results are given with special emphasis on thermal loop optimization. An appended section covers practical considerations for thermoelectric cooler-based control loops.
A large group of fiber optic lasers are powered by DC current. Laser drive is supplied by a current source with modulation added to the signal. The current source, although conceptually simple, constitutes an extraordinarily tricky design problem. There are a number of practical requirements for a fiber optic current source and failure to consider them can cause laser and/or optical component destruction. This application note describes ten laser current source circuits with a range of capabilities. High and low current types are presented, along with designs for grounded anode, cathode or floating operation. Each circuit also includes laser protection features. Appended sections cover laser load simulation and current source noise measurement techniques.
Avalanche photodiodes, used in laser based fiberoptic systems, require high voltage bias and accurate, wide range current monitoring. Bias voltage varies from 15V-90V and current ranges from 100nA to 1mA, a 10,000:1 dynamic range. This publication presents various 5 volt powered circuits which meet these requirements. Appended sections detail specific circuit techniques and cover measurement practice.
This publication concerns implementation of high quality "Flash" illumination in cellular telephones/cameras. Performance vs LED based illumination is discussed and flashlamp operation reviewed. Considerations for support circuitry are given, and a practical circuit, accompanied by performance data, is described. Layout and RFI issues are treated and a sample layout provided. An appended section details operation of the LT3468 flash capacitor charger used in the text's circuit and lists appropriate magnetic components.
Eighteen circuits are presented in this compilation. Signal sources include a voltage controlled current source, an amplitude/frequency stabilized sine wave oscillator, a versatile, 0V to 50V wideband level shift and four sub-nanosecond pulse generators with risetimes as low as 20ps. Five signal a unique, single positive rail powered amplifier with output to (and below) zero volts, a milliohmmeter, a 0.02% accurate instrumentation amplifier with 120dB CMRR at 125VCM, a 100MHz switch with 5mV control channel feedthrough and a 5V powered, 15ppm linearity quartz stabilized V&F, converter. The power circuits section features a Xenon flashlamp supply, two 5V powered, 0V to 300V DC/DC converters, a fixed 200V output circuit for APD bias, a 100W 0V to 500V, 28V powered converter and a high current paralleling scheme for linear regulators. Two appended sections consider measurement technique and connection practice in sub-nanosecond circuits.
Linear regulators are commonly employed to post-regulate switching regulator outputs. Benefits include improved stability, accuracy, transient response and lowered output impedance. Ideally, these performance gains would be accompanied by markedly reduced switching regulator generated ripple and spikes. In practice, all linear regulators encounter some difficulty with ripple and spikes, particularly as frequency rises. This publication explains the causes of linear regulators' dynamic limitations and presents board level techniques for improving ripple and spike rejection. A hardware based ripple/spike simulator is presented, enabling rapid breadboard testing under various conditions. Three appendices review ferrite beads, inductor based filters and probing practice for wideband, sub-millivolt signals.
This application note provides an extensive guideline for the thermal performance of the LTM4600 &Module. The LTM4600 is characterized with and without heatsinking over an extended operating temperature range. De-rating curves are derived with the different heatsinking types, and the equivalent &JA (thermal resistance) is derived. The different &JA parameters are tabulated with reference to the different test conditions.
Semiconductor memory, card readers, microprocessors, discdrives, piezoelectric devices and digitally based systems furnishtransient loads that a voltage regulator must service. Ideally,regulator output is invariant during a load transient. In practice,some variation is encountered and becomes problematic if allowableoperating voltage tolerances are exceeded. This mandatestesting the regulator and its associated support components toverify desired performance under transient loading conditions.Various methods are employable to generate transient loads,allowing observation of regulator response. This application notepresents open and closed loop transient load testing circuitrywith measured performance taken under various conditions.Practical considerations for a memory supply voltage regulatorare reviewed. Four appended sections cover capacitor parasiticsand their effects on load transient response, output capacitor selection,probing techniques and a stabilized transient load tester.
The voltage range of Linear Technology's PowerPath circuits can be easily extended with just a few components, thus allowing them to meet the needs of virtually all applications. This application note presents solutions for circuits that must withstand large negative voltages, a reverse adapter input for example, and circuits that must withstand large positive inputs, such as automotive load-dump.
The LTC3207/LTC3207-1 is a 600mA LED/Camera driver which illuminates 12 Universal LEDs (ULEDs) and one camera flash LED. The (ULEDs) are considered universal because they may be individually turned on or off, set in general purpose output (GPO) mode, set to blink at a selected on-time and period, or gradate on and off at a selected gradation rate. This device also has an external enable (ENU) pin that may be used to blink, gradate, or turn on/off the LEDs without using the I2C bus. This may be useful if the microprocessor is in sleep or standby mode. If used properly, these features may save valuable memory space, programming time, and reduce the I2C traffic.
This application note provides an extensive guideline for the thermal performance of the LTM4601 &Module. The LTM4601 is characterized with and without heatsinking over an extended operating temperature range. De-rating curves are derived with the different heatsinking types, and the equivalent &JA (thermal resistance) is derived. The different &JA parameters are tabulated with reference to the different test conditions.
The LTC3219 is a 250mA LED driver which illuminates 9 Universal LEDs (ULEDs). The ULEDs are considered universal because they may be individually turned on or off, set in general purpose output (GPO) mode, set to blink at a selected on-time and period, or gradate on and off at a selected gradation rate. This device also has an external enable (ENU) pin that may be used to blink, gradate, or turn on/off the LEDs without using the I2C bus. This may be useful if the microprocessor is in sleep or standby mode. If used properly, these features may save valuable memory space, programming time, and reduce I2C traffic.
Automobiles, aircraft, marine vehicles, uninterruptible power supplies and telecom hardware represent areas utilizing series connected battery stacks. These stacksof individual cells may contain many units, reaching potentials of hundreds of volts. In such systems it is often desirable to accurately determine each individual cell&s voltage. Obtaining this information in the presence of the high "common mode" voltage generated by the batterystack is more difficult than might be supposed.
This ink marks LTC&s eighth circuit collection publication.1 We are continually surprised, to the point of near mystification, by these circuit amalgams seemingly limitless appeal. Reader requests ascend rapidly upon publication, remaining high for years, even decades. All LTC circuit collections, despite diverse content, share this popularity, although just why remains an open question. Why is it? P compact, complete, succinct and insular. Perhaps the freedom of selection without commitment, akin to window shopping. Or, perhaps, simply the pleasure of new recruits for the circuit aficionados intellectual palate. Locally based electrosociolgists, spinning elegantly contrived theories, offer explanation, but no convincing evidence is at hand. What is certain is that readers are attracted to these compendiums and that calls us to attention. As such, in accordance with our mission to serve customer preferences, this latest collection is presented. Enjoy.
This application note illustrates how to program and use the unique features of the LTC3220/LTC3220-1 Universal LED (ULED) Driver. These features include individually controlling, gradually turning on and off, or blinking up to 18 LEDs. This device may also be used to provide digital signal(s) to other devices while in shutdown using a strong pull-down general purpose output (GPO) and an external power source. Current limited GPO mode may also be used to control other devices using the charge pump output (CPO) of the device or an external supply. A programmable shutdown feature allows the device to go into and out of shutdown returning to its pre-shutdown state. These features give the user vast flexibility and control of LEDs and other devices while saving memory space, programming time, I2C traffic, and even battery power.
The LTM8020, LTM8021, LTM8022 and LTM8023 &Modules are complete easy-to-use encapsulated step down DC/DC regulators intended to take the pain and aggravation out of implementing a switching power supply onto a system board. With a &Module, you only need an input cap, output cap and one or two resistors to complete the design. As one might imagine, this high level of integration greatly simplifies the task of printed circuit board design, reducing the effort to four categories: component footprint generation, component placement, routing the nets, and thermal vias.
Photomultipliers (PMT), avalanche photodiodes (APD), ultrasonic transducers, capacitance microphones, radiation detectors and similar devices require high voltage, low current bias. Additionally, the high voltage must be pris well under a millivolt is a common requirement with a few hundred microvolts sometimes necessary. Normally, switching regulator configurations cannot achieve this performance level without employing special techniques. One aid to achieving low noise is that load currents rarely exceed 5mA. This freedom permits output filtering methods that are usually impractical.
In a recent discussion with a system designer, the re- quirement for his power supply was to regulate 1.5V and deliver up to 40A of current to a load that consisted of four FPGAs. This is up to 60W of power that must be delivered in a small area with the lowest profile (height) possible to allow a steady flow of air for cooling. The power supply had to be surface mountable and operate at high enough efficiency to minimize heat dissipation. He also demanded the simplest possible solution so his time could be dedicated to the more complex tasks. Aside from precise electrical performance, this solution had to remove the heat generated during DC to DC conversion quickly so that the circuit and the ICs in the vicinity do not over heat.
In part one of this article, we discussed the circuit and electrical performance of a compact and low profile 48A, 1.5V DC/DC regulator solution for a four-FPGA design. The new approach uses four DC/DC &Module& regulators in parallel (Figure 1) to increase output current while sharing the current equally among each device. This solution relies on the accurate current sharing of these &Module regulators to prevent hot-spots by dissipating the heat evenly over a compact surface area. Each DC/DC &Module is a complete power supply with on-board inductor, DC/DC controller, MOSFETs, compensation circuitry and input/output bypass capacitors. It occupies only 15mm & 15mm of board area and has a low profile (height) of only 2.8mm. This low profile allows air to flow smoothly over the entire circuit. Moreover, this solution casts no thermal shadow on its surrounding components, further assisting in optimizing thermal performance of the entire system.
Most circuit designers are familiar with diode dynamic characteristics such as charge storage, voltage dependent capacitance and reverse recovery time. Less commonly acknowledged and manufacturer specifi ed is diode forward turn-on time. This parameter describes the time required for a diode to turn on and clamp at its forward voltage drop. Historically, this extremely short time, units of nanoseconds, has been so small that user and vendor alike have essentially ignored it. It is rarely discussed and almost never specified. Recently, switching regulator clock rate and transition time have become faster, making diode turn-on time a critical issue.
Data Conversion Application Notes
Analog-to-digital conversion circuits which directly digitize low level transducer outputs, without DC preamplification, are presented. Covered are circuits which operate with thermocouples, strain gauges, humidity sensors, level transducers and other sensors.
1.5V powered circuits for complex linear functions are detailed. Designs include a V/F converter, a 10-bit A/D, sample-hold amplifiers, a switching regulator and other circuits. Also included is a section of component considerations for 1.5V powered linear circuits.
A tutorial on SAR type A/D converters, this note contains detailed information on several 12-bit circuits. Comparator, clocking, and preamplifier designs are discussed. A final circuit gives a 12-bit conversion in 1.8&s. Appended sections explain the basic SAR technique and explore D/A considerations.
A collection of interface applications between various microprocessors/ controllers and the LTC1090 family of data acquisition systems. The note is divided into sections specific to each interface.
This application note describes a Linear Technology "Half-Flash" A/D converter, the LTC1099, being connected to a 256 element line scan photodiode array. This technology adapts itself to handheld (i.e., low power) bar code readers, as well as high resolution automated machine inspection applications.
A complete design for a data acquisition card for the IBM PC is detailed in this application note. Additionally, C language code is provided to allow sampling of data at speed of more than 20kHz. The speed limitation is strictly based on the execution speed of the "C" data acquisition loop. A "Turbo" XT can acquire data at speeds greater than 20kHz. Machines with 80286 and 80386 processors can go faster than 20kHz. The computer that was used as a test bed in this application was an XT running at 4.77MHz and therefore all system timing and acquisition time measurements are based on a 4.77MHz clock speed.
A collection of interface applications between various microprocessors/ controllers and the LTC1290 family of data acquisition systems. The note is divided into sections specific to each interface.
A variety of measurement and control circuits are included in this application note. Eighteen circuits, including ultra low noise amplifiers, current sources, transducer signal conditioners, oscillators, data converters and power supplies are presented. The circuits emphasize precision specifications with relatively simple configurations.
This application note consolidates the circuits from the first few years of Linear Technology magazine into one publication. Presented in the note are a variety of circuits ranging from a 50W high efficiency (&90%) switching regulator to steep roll-off filter circuits with low distortion to 12-bit differential temperature measurement systems.
This application note presents a wide variety of data acquisition circuits. The detailed circuit schematics cover 8-, 10-, and 12- bit ADC and DAC applications, serial and parallel digital interfaces, battery monitoring, temperature sensing, isolated interfaces, and connections to various popular microprocessors and microcontrollers. An appendix covers suggested voltage references.
Application Note 67 is a collection of circuits for data conversion, interface and signal processing from the first five years of Linear Technology. This application note includes circuits such as fast video multiplexers for high speed video, an ultraselective bandpass filter circuit with adjustable gain, and a fully differential, 8-channel, 12-bit A/D system. The categories included in this app note are data conversion, interface, filters, instrumentation, video/op amps and miscellaneous circuits.
This application note describes proper techniques for applying high performance ADCs. It describes the problems designers encounter, how to recognize their symptoms and how to avoid them. Topics include ground planes and grounding, supply and reference bypassing, analog input signal conditioning, sampling clock generation, signal jitter and proper handling of the data outputs. A sample board layout is provided as well as performance curves showing the effects of correct and incorrect application.
DAC DC specifications are relatively easy to verify. AC specifications require more sophisticated approaches to produce reliable information. In particular, the settling time of the DAC and its output amplifier is extraordinarily difficult to determine to 16-bit resolution. This application note presents methods for 16-bit DAC settling time measurement and compares results. Appendices discuss oscilloscope overdrive, frequency compensation, circuit and optimization techniques, layout, power stages and a historical perspective of precision DACs.
This application note describes six low power differential-tosingle- ended signal conditioning circuits for the LTC2400 No Latency &D&STM 24-bit ADC. These circuits offer the customer a number of choices for conditioning differential input signals as low as 5mV to as high as &2.5V, as well as operation on a single 5V or &5V supplies. Each circuit description also covers circuit design and implementation techniques that can help preserve the LTC2400's inherently high effective resolution. AN78 concludes with two circuits for digitizing temperature when using an RTD or Type S thermocouple.
Linear Technology's LTC2400 is the world's first 24-bit ADC in an SO-8 package. An innovative new delta-sigma architecture has been developed. The result is a small, highly accurate, simple-to-use delta-sigma ADC. This Application Note was created to educate users on several topics associated with delta-sigma converters and to dispel confusion associated with this new oneshot, or No Latency &D&STM architecture. The key topics addressed include speed, noise, PGAs line frequency rejection, input current, multiplexing, analog input range and key features differentiating the LTC2400 from other delta-sigma ADCs.
This publication details a true 1ppm D-to-A converter. Total DC error of this processor corrected DAC remains within 1ppm from 18-32&C, including reference drift. DAC error exclusive of reference drift is substantially better. Construction details and performance verification techniques are included, along with a complete software listing.
Application Note 87 is the fifth in a series that excerpts useful circuits from Linear Technology magazine. Data conversion, interface and signal conditioning circuits from issue VI:1 (February 1996) through issue VIII:4 (November 1998) are featured. Like its predecessor, AN67, this Application Note includes circuits for high speed video, interface and hot swap circuits, active RC and switched capacitor filter circuitry and a variety of data conversion and instrumentation circuits. All circuits are conveniently indexed by type.
AN96 features several applications that demonstrate how to take full advantage of Linear Technology's delta sigma ADCs when interfacing to sensors. In many cases, signal conditioning can be greatly simplified or eliminated completely. This note explains where it is appropriate to use amplifiers and how to optimize amplifier gain. Also included are discussions on measuring effective number of bits (ENOB) and the relationship to instrument performance, frequency response of delta sigma ADCs, and test techniques. C source code for all of the applications is included to aid firmware development.
This ink marks LTC&s eighth circuit collection publication.1 We are continually surprised, to the point of near mystification, by these circuit amalgams seemingly limitless appeal. Reader requests ascend rapidly upon publication, remaining high for years, even decades. All LTC circuit collections, despite diverse content, share this popularity, although just why remains an open question. Why is it? P compact, complete, succinct and insular. Perhaps the freedom of selection without commitment, akin to window shopping. Or, perhaps, simply the pleasure of new recruits for the circuit aficionados intellectual palate. Locally based electrosociolgists, spinning elegantly contrived theories, offer explanation, but no convincing evidence is at hand. What is certain is that readers are attracted to these compendiums and that calls us to attention. As such, in accordance with our mission to serve customer preferences, this latest collection is presented. Enjoy.
Signal Conditioning Application Notes
This application note describes a wide range of useful applications for the LTC1043 dual precision instrumentation switched capacitor building block. Some of the applications described are ultra high performance instrumentation amplifier, lock-in amplifier, wide range digitally controlled variable gain amplifier, relative humidity sensor signal conditioner, LVDT signal conditioner, charge pump F/V and V/F converters, 12-bit A/D converter and more.
The LTmA power buffer is described in a number of useful applications such as boosted op amp, a feed-forward, wideband DC stabilized buffer, a video line driver amplifier, a fast sample-hold with hold step compensation, an overload protected motor speed controller, and a piezoelectric fan servo.
6 applications utilizing thermally based circuits are detailed. Included are a 50MHz RMS to DC converter, and anemometer, a liquid flow meter and others. A general discussion of thermodynamic considerations involved in circuitry is also presented.
Application considerations and circuits for the LT1001 and LT1002 single and dual precision amplifiers are illustrated in a number of circuits, including strain gauge signal conditioners, linearized platinum RTD circuits, an ultra precision dead zone circuit for motor servos and other examples.
A discussion of circuit, layout and construction considerations for low level DC circuits includes error analysis of solder, wire and connector junctions. Applications include sub-microvolt instrumentation and isolation amplifiers, stabilized buffers and comparators and precision data converters.
The AN10 begins with a survey of methods for measuring op amp settling time. This commentary develops into circuits for measuring settling time to 0.0005%. Construction details and results are presented. Appended sections cover oscilloscope overload limitations and amplifier frequency compensation.
Circuits for clock sources are presented. Special attention is given to crystal-based designs including TXCOs and VXCOs.
The AN13 is an extensive discussion of the causes and cures of problems in very high speed comparator circuits. A separate applications section presents circuits, including a 0.025% accurate 1Hz to 30MHz V/F converter, a 200ns 0.01% sample-hold and a 10MHz fiber-optic receiver. Five appendices covering related topics complete this note.
A variety of high performance V/F circuits is presented. Included are a 1Hz to 100MHz design, a quartz-stabilized type and a 0.0007% linear unit. Other circuits feature 1.5V operation, sine wave output an nonlinear transfer functions. A separate section examines the trade-offs and advantages of various approaches to V/F conversion.
1.5V powered circuits for complex linear functions are detailed. Designs include a V/F converter, a 10-bit A/D, sample-hold amplifiers, a switching regulator and other circuits. Also included is a section of component considerations for 1.5V powered linear circuits.
This note describes some of the unique IC design techniques incorporated into a fast, monolithic power buffer, the LT1010. Also, some application ideas are described such as capacitive load driving, boosting fast op amp output current and power supply circuits.
This note presents output state circuits which provide power gain for monolithic amplifiers. The circuits feature voltage gain, current gain, or both. Eleven designs are shown, and performance is summarized. A generalized method for frequency compensation appears in a separate section.
Discusses the principles of operation of the LTC1062 and helpful hints for its application. Various application circuits are explained in detail with focus on how to cascade two LTC1062s and how to obtain notches. Noise and distortion performance are fully illustrated.
Applications often require an amplifier that has extremely high performance in several areas. For example, high speed and DC precision are often needed. If a single device cannot simultaneously achieve the desired characteristics, a composite amplifier made up of two (or more) devices can be configured to do the job. AN21 shows examples of composite approaches in designs combining speed, precision, low noise and high power.
AN22 details the theoretical and application aspects of the LT1088 thermal RMS/DC converter. The basic theory behind thermal RMS/DC conversion is discussed and design details of the LT1088 are presented. Circuitry for RMS/DC converters, wideband input buffers and heater protection is shown.
Low power operation of electronic apparatus has become increasingly desirable. AN23 describes a variety of low power circuits for transducer signal conditioning. Also included are designs for data converters and switching regulators. Three appended sections discuss guidelines for micropower design, strobed power operation and effects of test equipment on micropower circuits.
Highlights the LTC1062 as a lowpass filter in a phase lock loop. Describes how the loop's bandwidth can be increased and the VCO output jitter reduced when the LTC1062 is the loop filter. Compares it with a passive RC loop filter. Also discussed is the use of LTC1062 as simple bandpass and bandstop filter.
Presents two methods of designing high quality switched capacitor bandpass filters. Both methods are intended to vastly simplify the mathematics involved in filter design by using tabular methods. The text assumed no filter design experience but allows high quality filters to be implemented by techniques not presented before in the literature. The designs are implemented by numerous examples using devices from LTC's Switched- Capacitor filter family: LTC1060, LTC1061, and LTC1064. Butterworth and Chebyshev bandpass filters are discussed.
Considerations for thermocouple-based temperature measurement are discussed. A tutorial on temperature sensors summarizes performance of various types, establishing a perspective on thermocouples. Thermocouples are then focused on. Included are sections covering cold-junction compensation, amplifier selection, differential/isolation techniques, protection, and linearization. Complete schematics are given for all circuits. Processor- based linearization is also presented with the necessary software detailed.
This note is the manual for FCAD, a computer-aided design program for designing filters with LTC's switched-capacitor filter family. FCAD helps users design good filters with a minimum amount of effort. The experienced filter designer can use the program to achieve better results by providing the ability to play "what if" with the values and configuration of various components.
This note presents guidelines for circuits utilizing LTC's switched capacitor filters. The discussion focuses on how to optimize filter performance by optimizing the printed wiring board, the power supply, and the output buffering of the filter. Many additional topics are discussed such as how to select the proper filter response for the application and how to characterize a filter's THD for DSP applications.
This note provides answers to some of the more common questions concerning LTC's Macromodel Library. Topics include hardware and software requirements, model characteristics, and limitations and interpretation of results.
A wide variety of voltage reference circuits are detailed in this extensive guidebook of circuits. The detailed schematics cover simple and precision approaches at a variety of power levels. Included are 2 and 3 terminal devices in series and shunt modes for positive and negative polarities. Appended sections cover resistor and capacitor selection and trimming techniques.
Subtitled "Marrying Gain and Balance," this note covers signal conditioning circuits for various types of bridges. Included are transducer bridges, AC bridges, Wien bridge oscillators, Schottky bridges, and others. Special attention is given to amplifier selection criteria. Appended sections cover strain gauge transducers, understanding distortion measurements, and historical perspectives on bridge readout mechanisms and Wein bridge oscillators.
A variety of measurement and control circuits are included in this application note. Eighteen circuits, including ultra low noise amplifiers, current sources, transducer signal conditioners, oscillators, data converters and power supplies are presented. The circuits emphasize precision specifications with relatively simple configurations.
This application note, subtitled "A Designer's Companion for Wideband Circuitry," is intended as a reference source for designing with fast amplifiers. Approximately 150 pages and 300 figures cover frequently encountered problems and their possible causes. Circuits include a wide range of amplifiers, filters, oscillators, data converters and signal conditioners. Eleven appended sections discuss related topics including oscilloscopes, probe selection, measurement and equipment considerations, and breadboarding techniques.
LTC's op amp macromodels are described in detail, along with the theory behind each model and complete schematics of each topology. Extended modeling topics are discussed, such as phase/frequency response modifications and asymmetric slew rate for JFET op amp models. LTC's macromodels are optimized for accuracy and fast simulation times. Simulation times can be further reduced by using streamlining techniques found throughout AN48.
This application note discusses a variety of approaches for interfacing analog signals to 5V powered systems. Synthesizing a "rail-to-rail" op amp and scaling techniques for A/D converters are covered. A voltage-to-frequency converter, applicable where high resolution is required, is also presented.
The pace of the world of digital communications is increasing at a tremendous rate. Each day the engineer is requested to compact more data in the same channel bandwidth with closer channel spacing. This application note discusses some of the requirements and techniques for using the new LTC and LTC1264-7 filters which were designed specifically for digital communications. The terms "channel bandwidth," "eye diagrams" and "linear phase" filtering are discussed without the need for the "engineering speak" which permeates many textbook explanations of the same subjects.
AN57, the Video Circuit Collection, features a variety of video circuits designed at LTC. The LT1204 70MHz multiplexer is featured in a number of circuits which require excellent video isolation from channel to channel. High speed voltage and current feedback amplifiers are highlighted throughout the section on video processing circuits. There is a section on applying Current Feedback Amplifiers (CFAs) and a number of articles taken from the Linear Technology magazine.
This collection of circuits was worked out between June 1991 and July of 1994. Most were designed at customer request or are derivatives of such efforts. Types of circuits include power converters, transducer signal conditioners, amplifiers and signal generators. Specific circuits include low noise amplifiers, high power single cell DC/DC converters, portable high accuracy barometers, a 10mHz 1% accuracy RMS/DC converter, and random noise generators. Appended sections cover noise theory and present a historical perspective of wideband amplifiers.
Application Note 67 is a collection of circuits for data conversion, interface and signal processing from the first five years of Linear Technology. This application note includes circuits such as fast video multiplexers for high speed video, an ultraselective bandpass filter circuit with adjustable gain, and a fully differential, 8-channel, 12-bit A/D system. The categories included in this app note are data conversion, interface, filters, instrumentation, video/op amps and miscellaneous circuits.
AN72 is an extensive discussion of the causes and cures of problems in very high speed comparator circuits. A separate applications section uses the 7ns LT1394 in V-to-F converters, crystal oscillators, clock skew generators, triggers, sampling configurations and a nanosecond pulse stretcher. Appendices cover related topics.
This publication includes designs for data converters and signal conditioners, transducer circuits, crystal oscillators and power converters. Wideband and micropower circuitry receive special attention. Tutorials on micropower design techniques and parasitic effects of test equipment are included.
AN79 modifies methods presented in AN74, permitting verification of 30 nanosecond amplifier settling times to 0.1% resolution. The sampling-based technique used is detailed and results presented. Appendices cover oscilloscope overdrive issues, construction of a subnanosecond rise time pulse generator, amplifier compensation, circuit construction and calibration procedures.
Just how do bandgaps and buried Zeners stack up against Weston cells? Did you know your circuit board may induce more drift in a reference than time and temperature? Learn the answers to these and other commonly asked reference questions ranging from burn-in recommendations to &DVBE generation in this Application Note.
Application Note 87 is the fifth in a series that excerpts useful circuits from Linear Technology magazine. Data conversion, interface and signal conditioning circuits from issue VI:1 (February 1996) through issue VIII:4 (November 1998) are featured. Like its predecessor, AN67, this Application Note includes circuits for high speed video, interface and hot swap circuits, active RC and switched capacitor filter circuitry and a variety of data conversion and instrumentation circuits. All circuits are conveniently indexed by type.
Instrumentation applications for a monolithic programmable oscillator are presented in this publication. Circuits include platinum and thermistor based thermometers, an isolated thermometer and three relative humidity signal conditioners. Bipolar and FET input chopper stabilized amplifiers with noise below 45nV (0.1Hz to 10Hz) are detailed. Two clock tunable sine wave generators with settable amplitude appear, as well as a tunable notch filter, an interval generator and an A to D converter. The oscillator's performance is contrasted against other approaches and its interval operation discussed.
Wideband amplifiers achieve slew rates beyond 2500V/&s. Verifying slew rates at this speed requires special techniques. In particular, a subnanosecond rise time input step is necessary for accurate slew rate measurement. A pulse generator with a 360 picosecond rise time is shown, and its construction detailed. Slew rate test results using this generator are presented and compared to data taken with slower rise time generators. Appendices cover high speed measurement technique, generator output level shifting and picosecond signal path construction considerations.
Eighteen circuits are presented in this compilation. Signal sources include a voltage controlled current source, an amplitude/frequency stabilized sine wave oscillator, a versatile, 0V to 50V wideband level shift and four sub-nanosecond pulse generators with risetimes as low as 20ps. Five signal a unique, single positive rail powered amplifier with output to (and below) zero volts, a milliohmmeter, a 0.02% accurate instrumentation amplifier with 120dB CMRR at 125VCM, a 100MHz switch with 5mV control channel feedthrough and a 5V powered, 15ppm linearity quartz stabilized V&F, converter. The power circuits section features a Xenon flashlamp supply, two 5V powered, 0V to 300V DC/DC converters, a fixed 200V output circuit for APD bias, a 100W 0V to 500V, 28V powered converter and a high current paralleling scheme for linear regulators. Two appended sections consider measurement technique and connection practice in sub-nanosecond circuits.
Sensing and/or controlling current flow is a fundamental requirement in many electronics systems, and the techniques to do so are as diverse as the applications themselves. This Application Note compiles solutions to current sensing problems and organizes the solutions by general application type. These circuits have been culled from a variety of Linear Technology documents.
It is widely acknowledged that RMS measurement of waveforms furnishes the most accurate amplitude information. Rectify-andaverage schemes, usually calibrated to a sine wave, are only accurate for one waveshape. Departures from this waveshape result in pronounced errors. Although accurate, RMS conversion often entails limited bandwidth, restricted range, complexity and difficult to characterize dynamic and static errors. The LTC RMS converter family addresses these issues, making instrument grade applications practical. A variety of instrumentation oriented applications are presented. Included are basic circuits, a fully isolated AC line monitor, a distortionless AC line voltage regulator, wideband X1000 pre-amplifiers, a quartz crystal RMS current meter, a crystal stabilized AC voltage reference, an RMS amplitude leveled random noise generator and an RMS amplitude level controller. Appended sections cover RMS theory and converter operation, AC measurement and signal handling practice, test equipment recommendations, noise theory and noise diodes.
Automobiles, aircraft, marine vehicles, uninterruptible power supplies and telecom hardware represent areas utilizing series connected battery stacks. These stacks of individual cells may contain many units, reaching potentials of hundreds of volts. In such systems it is often desirable to accurately determine each individual cell&s voltage. Obtaining this information in the presence of the high "common mode" voltage generated by the battery stack is more difficult than might be supposed.
This ink marks LTC&s eighth circuit collection publication.1 We are continually surprised, to the point of near mystification, by these circuit amalgams seemingly limitless appeal. Reader requests ascend rapidly upon publication, remaining high for years, even decades. All LTC circuit collections, despite diverse content, share this popularity, although just why remains an open question. Why is it? P compact, complete, succinct and insular. Perhaps the freedom of selection without commitment, akin to window shopping. Or, perhaps, simply the pleasure of new recruits for the circuit aficionados intellectual palate. Locally based electrosociolgists, spinning elegantly contrived theories, offer explanation, but no convincing evidence is at hand. What is certain is that readers are attracted to these compendiums and that calls us to attention. As such, in accordance with our mission to serve customer preferences, this latest collection is presented. Enjoy.
Frequently, voltage reference stability and noise defi ne measurement limits in instrumentation systems. In particular, reference noise often sets stable resolution limits. Reference voltages have decreased with the continuing drop in system power supply voltages, making reference noise increasingly important. The compressed signal processing range mandates a commensurate reduction in reference noise to maintain resolution. Noise ultimately translates into quantization uncertainty in A to D converters, introducing jitter in applications such as scales, inertial navigation systems, infrared thermography, DVMs and medical imaging apparatus. A new low voltage reference, the LTC6655, has only 0.3ppm (775nV) noise at 2.5VOUT.
Interface Application Notes
Application Note 67 is a collection of circuits for data conversion, interface and signal processing from the first five years of Linear Technology. This application note includes circuits such as fast video multiplexers for high speed video, an ultraselective bandpass filter circuit with adjustable gain, and a fully differential, 8-channel, 12-bit A/D system. The categories included in this app note are data conversion, interface, filters, instrumentation, video/op amps and miscellaneous circuits.
Application Note 87 is the fifth in a series that excerpts useful circuits from Linear Technology magazine. Data conversion, interface and signal conditioning circuits from issue VI:1 (February 1996) through issue VIII:4 (November 1998) are featured. Like its predecessor, AN67, this Application Note includes circuits for high speed video, interface and hot swap circuits, active RC and switched capacitor filter circuitry and a variety of data conversion and instrumentation circuits. All circuits are conveniently indexed by type.
High Frequency Application Notes
AN91 describes an RF feedback coupling method which eliminates the directional coupler. Instead, a 0.4pF &0.05pF capacitor and 50&O resistor are used to feed RF signal back to the LTC power controller. This method reduces coupling loss variations, cost and lead time.
Accurate measurement of the third order intercept point for low distortion IC products such as the LT5514 requires certain precautions to be observed in the test setup and testing procedure. The LT5514 linearity performance is high enough to push the test equipment and test set-up to their limits. A method for accurate measurement of third order intermodulation products, IM3, with standard test equipment is outlined below.
ACPR (adjacent channel power ratio) and AltCPR (alternate channel power ratio) are both measures of spectral regrowth. They are important performance metrics for digital communication systems that use, for example, WCDMA (wideband code division multiple access) modulation. This publication highlights key considerations for accurate measurements of these parameters. In particular, highly linear direct I/Q modulators such as the LT5528 require high performance measurement equipment and careful techniques to characterize their spectral regrowth.
This Application Note describes a method to accuratelymeasure internal and external phase and timing errors fora high performance direct I/Q modulator. A direct I/Qmodulator, such as the LT5528, translates baseband I andQ signals to RF, and combines them to produce a modulatedsingle sideband signal with (ideally) minimal residualcarrier (LO feedthrough) and image signals (undesiredsideband). In an ideal I/Q modulator, with perfect 90&phase shift between the I mixer and Q mixer local oscillators(LOI and LOQ), and with no other undesired phase andgain impairments, the modulator output will contain onlythe desired sideband. In practice, this is very difficult toaccomplish. For example, with a requirement of &60dBcimage suppression, the residual I-Q phase error is requiredto be below 0.16&. In practice, there are other sourcesof phase error, particularly in the baseband signal processing.
Linear Technology&s High Frequency Product lineupincludes a variety of RF I/Q modulators. The purpose ofthis application note is to illustrate the circuits requiredto interface these modulators with several popular D/Aconverters. Such circuits typically are required to maximizethe voltage transfer from the DAC to the baseband inputsof the modulator, as well as provide some reconstruction filtering.