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Application Notes

• Download
  High Voltage, Low Noise, DC/DC Converters &mdash AN118
  PDF, 2.6 Mb, File published: Mar 28, 2008
  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 pristinely free of noise; 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.
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  Application Note 118
  March 2008
  High Voltage, Low Noise, DC/DC Converters
  A Kilovolt with 100 Microvolts of Noise
  Jim Williams This publication describes a variety of circuits featuring
  outputs from 200V to 1000V with output noise below 100ВµV
  measured in a 100MHz bandwidth. Special techniques
  enable this performance, most notably power stages
  optimized to minimize high frequency harmonic content.
  Although sophisticated, all examples presented utilize
  standard, commercially available magnetics—no custom
  components are required. This provision is intended to
  assist the user in quickly arriving at a produceable design.
  Circuits and their descriptions are presented beginning
  with the next ink.
  BEFORE PROCEEDING ANY FURTHER, THE READER
  IS WARNED THAT CAUTION MUST BE USED IN THE
  CONSTRUCTION, TESTING AND USE OF THE TEXT’S
  CIRCUITS. HIGH VOLTAGE, LETHAL POTENTIALS ARE
  PRESENT IN THESE CIRCUITS. EXTREME CAUTION
  MUST BE USED IN WORKING WITH, AND MAKING
  CONNECTIONS TO, THESE CIRCUITS. REPEAT: THESE
  CIRCUITS CONTAIN DANGEROUS, HIGH VOLTAGE …

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  A Monolithic Switching Regulator with 100ВµV Output Noise &mdash AN70
  PDF, 1.7 Mb, Language: en, File published: Oct 1, 1997
  This publication details circuitry and applications considerations for the LT1533 low noise switching regulator. Eleven DC/DC converter circuits are presented, some offering <100µV output noise in a 100MHz bandwidth. Tutorial sections detail low noise DC/DC design, measurement, probing and layout techniques, and magnetics selection.
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  Application Note 70
  October 1997
  A Monolithic Switching Regulator with 100ВµV Output Noise
  “Silence is the perfectest herald of joy .”
  Jim Williams INTRODUCTION
  Size, output flexibility and efficiency advantages have
  made switching regulators common in electronic apparatus. The continued emphasis on these attributes has
  resulted in circuitry with 95% efficiency that requires
  minimal board area. Although these advantages are welcome, they necessitate compromising other parameters. back to the driving source (“reflected” noise) and it is
  radiated. The multiple transmission paths combine with
  the high frequency content to make noise suppression
  difficult. Unconscionable amounts of bypass capacitors,
  ferrite beads, shields, Mu-metal and aspirin have been
  expended in attempts to ameliorate noise-induced effects. Switching Regulator “Noise”
  Something commonly referred to as “noise” is a primary
  concern. The switched mode power delivery that permits
  the aforementioned advantages also creates wideband
  harmonic energy. This undesirable energy appears as
  radiated and conducted components commonly labeled
  as “noise.” Actually, switching regulator output “noise” is
  not really noise at all, but coherent, high frequency residue
  directly related to the regulatorвЂ^TMs switching.1 Figure 1
  shows typical switching regulator output noise. Two distinct characteristics are present. The slow, ramping output …

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  Circuitry for Signal Conditioning and Power Conversion &mdash AN75
  PDF, 508 Kb, File published: Mar 1, 1999
  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.
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  Application Note 75
  March 1999
  Circuitry for Signal Conditioning and
  Power Conversion
  Designs From a Once Lazy Sabbatical
  Jim Williams
  Introduction
  Linear Technology has a sabbatical program. Every five
  years employees are granted sabbatical leave, which may
  last up to six weeks. You have 18 months from each five
  year employment anniversary to take the leave. Sabbatical
  is fully company paid and has no restrictions. The time is
  yours to do with as you please.
  People exercise all degrees of freedom with their sabbaticals. They go sailing, they go to South Sea islands, they ski
  some mountain nobody ever heard of, they trek in Nepal.
  Houses get fixed, cars restored and children played with.
  For my third sabbatical I resolved to do absolutely nothing.
  For the first time in my life I was really tired, and I knew it.
  A six week rest sounded just fine. I’d walk the dog and
  spend time with my wife and son. That’s it. No transistors,
  no resistors, no op amps and, above all, no writing. I was
  so written out the thought of picking up a pencil produced
  an instant headache. …

• Download
  Linear Technology Magazine Circuit Collection, Volume IV &mdash AN84
  PDF, 2.4 Mb, File published: Apr 1, 2000
  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.
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  Application Note 84
  April 2000 Linear Technology Magazine Circuit Collection, Volume IV
  Power Products
  Richard Markell, Editor
  INTRODUCTION
  Application Note 84 is the fourth in a series that excerpts
  useful circuits from Linear Technology magazine to preserve them for posterity. This application note highlights
  “power” circuits from issue VI:1 (February 1996) through
  issue VIII:4 (November 1998). Another application note
  will feature data conversion, interface and signal processing circuits from the same era. Like its predecessor, AN 66,
  this Application Note includes circuits that can power
  most any system you can imagine, from “server” power
  supplies that generate in excess of 50 amps to micropower systems for portable and handheld equipment.
  Also included are power converters that can be voltage programmed using Intel’s VID code. Charge pump converters, linear regulators and battery charger circuits are
  included here, with Li-Ion batteries receiving extra attention. There are, of course, circuits that cannot be so simply
  categorized. Come browse. I’ll get out of the way and let
  the authors describe their creations.
  Note: Article Titles appear in this application note exactly
  as they originally appeared in Linear Technology magazine. This may result in some inconsistency in the usage
  of terminology. TABLE OF CONTENTS
  Introduction . 1
  REGULATORS—SWITCHING (BUCK)
  New LTCВ®1435–LTC1439 DC/DC Controllers Feature Value and Performance . 4 …

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  Current Sources for Fiber Optic Lasers: A Compendium of Pleasant Current Events &mdash AN90
  PDF, 409 Kb, File published: Apr 1, 2002
  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.
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  Application Note 90
  April 2002
  Current Sources for Fiber Optic Lasers
  A Compendium of Pleasant Current Events
  Jim Williams, Linear Technology Corporation
  INTRODUCTION
  A large group of fiber optic lasers are powered by DC
  current. Laser drive is supplied by a current source with
  modulation added further along the signal path. 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. Protection features must be included to prevent laser and
  optical component damage. The laser, an expensive and
  delicate device, must be protected under all conditions,
  including supply ramp up and down, improper control
  input commands, open or intermittent load connections
  and “hot plugging.”
  Detailed Discussion of Performance Issues Design Criteria for Fiber Optic Laser Current Sources It is useful to expand on the above cursory discussion to
  clarify design goals. As such, each previously called out
  issue is treated in greater detail below. Figure 1 shows a conceptual laser current source. Inputs
  include a current output programming port, an output …

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  Slew Rate Verification for Wideband Amplifiers: The Taming of the Slew &mdash AN94
  PDF, 594 Kb, File published: May 1, 2003
  Wideband amplifiers achieve slew rates beyond 2500V/µs. 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.
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  Application Note 94
  May 2003
  Slew Rate Verification for Wideband Amplifiers
  The Taming of the Slew
  Jim Williams
  INTRODUCTION
  Slew rate defines an amplifier’s maximum rate of output
  excursion. This specification sets limits on undistorted
  bandwidth, an important capability in A/D driver applications. Slew rate also influences achievable performance in
  D/A output stages, filters, video amplification and data
  acquisition. Because of its importance, amplifier slew rate
  must be verified by measurement. Deriving a measurement approach requires understanding slew rate’s relationship to amplifier dynamics. total elapsed time from input application until the output
  arrives at and remains within a specified error band
  around the final value is the settling time.1 Amplifier Dynamic Response Historically, slew rate measurement has been relatively
  simple.2 Early amplifiers had slew rates of typically 1V/Вµs,
  with later versions sometimes reaching hundreds of
  volts/Вµs. Standard laboratory pulse generators easily supplied rise times well beyond amplifier speeds. As slew rates
  have crossed 1000V/µs, the pulse generator’s finite rise
  time has become a concern. A recent device, the LT1818
  (See Box Section, “A 2500V/µs Slew Rate Amplifier with Figure 1 shows that amplifier dynamic response components include delay, slew and ring times. The delay time is
  small and is almost entirely due to amplifier propagation
  delay. During this interval there is no output movement.
  During slew time the amplifier moves at its highest …

Design Notes

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  Off-Line Low Noise Power Supply Does Not Require Filtering to Meet FCC Emission Requirements &mdash DN175
  PDF, 113 Kb, File published: Mar 1, 1998
  Extract from the document

  advertisement Off-Line Low Noise Power Supply Does Not Require Filtering
  to Meet FCC Emission Requirements – Design Note 175
  Jim Williams
  Introduction
  Off-line power supplies require input п¬Ѓltering components to meet FCC emission requirements. Additionally, board layout is usually quite critical, requiring
  considerable experimentation even for experienced
  off-line supply designers. These considerations derive
  from the wideband harmonic energy generated by the fast switching of traditional off-line supplies. A new
  device, the LTВ®1533 low noise switching regulator,
  eliminates these issues by continuous, closed-loop
  control of voltage and current switching times.1 Additionally, the device’s push-pull output drive eliminates the flyback interval of conventional approaches.
  This further reduces harmonics and smooths input
  1 In depth coverage of this device, its use and performance verification appears
  in LTC Application Note 70, “A Monolithic Switching Regulator with 100μV Output
  Noise,” by Jim Williams. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
  of Linear Technology Corporation. All other trademarks are the property of their
  respective owners. T1 !
  GER
  !
  DAN LTAGE
  O
  V
  H …

Articles

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  LT1533 Ultralow Noise Switching Regulator for High Voltage or High Current Applications &mdash LT Journal
  PDF, 223 Kb, File published: Feb 1, 1998
  Extract from the document

  DESIGN IDEAS LT1533 Ultralow Noise Switching
  Regulator for High Voltage or
  High Current Applications
  by Jim Williams
  High Voltage Input Regulator The LT1533 switching regulator1, 2
  achieves 100ВµV output noise by using
  closed-loop control around its output switches to tightly control
  switching transition time. Slowing
  down switch transitions eliminates
  high frequency harmonics, greatly
  reducing conducted and radiated
  noise.
  The part’s 30V, 1A output transistors limit available power. It is possible
  to exceed these limits while maintaining low noise performance by
  using suitably designed output
  stages. The LT1533’s IC process limits
  collector breakdown to 30V. A complicating factor is that the transformer
  causes the collectors to swing to twice
  the supply voltage. Thus, 15V represents the maximum allowable input
  supply. Many applications require
  higher voltage inputs; the circuit in
  Figure 1 uses a cascoded3 output
  stage to achieve such high voltage …

Model Line

Manufacturer's Classification

• Power Management > Switching Regulator > Ultralow Noise Regulators