Datasheet Linear Technology LT1683

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Application Notes

• Download
  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.
  Extract from the document

  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 …

Articles

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  Reduce EMI with Ultralow Noise 48V to 5V, 10W DC/DC Converter &mdash LT Journal
  PDF, 209 Kb, File published: Feb 1, 2001
  Extract from the document

  DESIGN IDEAS Reduce EMI with Ultralow Noise 48V
  to 5V, 10W DC/DC Converter
  by Rick Brewster
  Introduction
  Increasingly, designers are using
  ultralow noise controllers to avoid
  EMI problems. Lower operating
  voltages and more sensitive measurements have created the need for
  quieter supplies. Extra filtering components and shielding are usually
  required, as is a careful board layout.
  Ultralow noise switching regulator
  controllers such as the LT1683 reduce
  or eliminate the need for extra filtering. The LT1683 controller uses
  external MOSFETs to create ultralow
  noise DC/DC converters. Control of
  the switch voltage and switch current
  slew rates reduces switcher noise.
  The LT1683’s use of external switches
  allows for greater flexibility in the
  selection of voltage and current ratings of the supply. + 39ВµF
  63V 2Вµs/DIV Figure 2. Voltage on one of the MOSFET drains and on the sense resistor Circuit Details T1 FZT649
  10ВµF
  20V …

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  Two New Switching Regulators Deliver Both Power and Ultralow Noise &mdash LT Journal
  PDF, 219 Kb, File published: Sep 1, 2001
  Extract from the document

  DESIGN FEATURES Two New Switching Regulators Deliver
  Both Power and Ultralow Noise
  by Rick Brewster
  Introduction
  T raditionally, when designers
  required a very low noise power supply, they would avoid DC/DC
  switchers because of their notorious
  reputation for generating high frequency harmonics. If they did use a
  switcher, careful attention would be
  required for board layout, shielding
  and the judicious use of filtering elements. The LT1683 and LT1738 are
  new switching regulator controllers
  that create a DC/DC switching supply with significantly lower conducted
  and radiated electromagnetic interference (EMI). These controllers
  reduce EMI at its source by controlling the current and voltage slew rates
  of the main switches. A robust DC/
  DC converter for use in noise-sensitive applications can be built with
  confidence.
  The LT1683 and LT1738 make use
  of a patented dual control loop method
  that allows for control of both the
  output switch voltage slew rate and 48V
  510Ω …

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Manufacturer's Classification

• Power Management > Switching Regulator > Ultralow Noise Regulators