Datasheet Linear Technology LT1946

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Application Notes

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  Bias Voltage and Current Sense Circuits for Avalanche Photodiodes &mdash AN92
  PDF, 1.1 Mb, File published: Nov 1, 2002
  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.
  Extract from the document

  Application Note 92
  November 2002
  Bias Voltage and Current Sense Circuits for
  Avalanche Photodiodes
  Feeding and Reading the APD
  Jim Williams, Linear Technology Corporation
  INTRODUCTION
  Avalanche photodiodes (APDs) are widely utilized in laser
  based fiberoptic systems to convert optical data into
  electrical form. The APD is usually packaged with a signal
  conditioning amplifier in a small module. An APD receiver
  module and attendant circuitry appears in Figure 1. The
  APD module (figure right) contains the APD and a transimpedance (e.g., current-to-voltage) amplifier. An optical
  port permits interfacing fiberoptic cable to the APD’s
  photosensitive portion. The module’s compact construction facilitates a direct, low loss connection between the
  APD and the amplifier, necessary because of the extremely
  high speed data rates involved.
  The receiver module needs support circuitry. The APD
  requires a relatively high voltage bias (figure left) to
  operate, typically 20V to 90V. This voltage is set by the bias
  supply’s programming port. This programming voltage
  may also include corrections for the APD’s temperature
  dependent response. Additionally, it is desirable to monitor the APD’s average current (figure center), which indi-cates optical signal strength. This information can be …

Articles

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  1.2MHz and 2.7MHz, 1.5A Boost Converters Drive Big LCDs, LEDs &mdash LT Journal
  PDF, 218 Kb, File published: Mar 1, 2002
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  DESIGN IDEAS 1.2MHz and 2.7MHz, 1.5A Boost
  Converters Drive Big LCDs, LEDs
  by Albert Wu Introduction Triple Output TFT Supply
  Figure 1 shows a typical triple output
  TFT supply. The main output of 8V
  can provide 375mA of output current. Charge pumps are used to
  generate the 23V and –8V outputs.
  Figure 2 shows the efficiency of the
  circuit as the 8V output load is varied. The efficiency graph includes the 85
  80
  75
  EFFICIENCY (%) is useful in applications where noise
  in the 1MHz region is unacceptable,
  such as DSL power supplies and automotive LED dash board backlights.
  Both parts include an integrated softstart function to keep the start-up
  inrush current well controlled. The
  LT1946 comes in the space saving
  MSOP-8 package with a maximum
  height of 1.1mm, and the LT1946A
  comes in a MSOP-8E thermally enhanced package. The LT1946/LT1946A is a step-up,
  or boost, DC/DC converter with a
  built-in 1.5A, 200mΩ switch. The
  minimum current limit of 1.5A is …

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Manufacturer's Classification

• Power Management > Switching Regulator > LCD/CCD/OLED Bias
• Power Management > Switching Regulator > Step-Up (Boost) Regulators > Internal Power Switch Boost