Datasheet Linear Technology LTC3805

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Design Notes

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  Negative Buck Converter with Short-Circuit Protection and Shutdown &mdash DN1022
  PDF, 109 Kb, File published: Sep 8, 2011
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  Negative Buck Converter with Short-Circuit Protection and Shutdown
  Design Note 1022
  Victor Khasiev
  Introduction
  Negative buck converters are increasingly used to “step
  down” (by absolute value) negative voltages. The main
  reason behind the increasing demand is the standardization
  of switching transformers, which are typically produced
  with one or two secondary windings. For example, if a
  system employs a transformer with two secondary windings to produce ±12V, and the design also requires –3.3V,
  engineers tend to lean toward solutions, such as a negative
  buck, that don’t require changing the main transformer.
  Circuit Description and Performance
  Figure 1 shows a negative buck converter that generates
  –3.3V at 3A from a –12V rail. The power train includes
  inductor L1, diode D1 and MOSFET Q1. The LTC3805-5
  controller IC includes a complete set of essential functions
  including short-circuit protection (the current level can
  be precisely set), converter enable/disable, and programmable switching frequency. An internal shunt regulator allows biasing the IC directly
  from the input rail. Despite the simplicity of the topology,
  which makes it an attractive choice for many designers,
  there are two important design considerations in a negative
  buck converter: sensing the output voltage and remote …

Articles

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  Current Mode Flyback DC/DC Controller Provides Tremendous Design Flexibility &mdash LT Journal
  PDF, 982 Kb, File published: Jan 28, 2008
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  L DESIGN FEATURES Current Mode Flyback DC/DC
  Controller Provides Tremendous
  by Arthur Kelley
  Design Flexibility
  Introduction
  By its nature, a flyback DC/DC converter is one of the most versatile power
  converter topologies. Because it uses
  a transformer, it can step up or step
  down voltages and provide DC isolation
  if needed. Applications include power
  supplies for networking equipment,
  Power-over-Ethernet (PoE), automotive, consumer and general system
  house keeping. The LTC3805 has been
  designed to enhance the flexibility of
  the basic flyback converter, making
  it possible to optimize a single design
  for diverse applications. The converter
  input and output voltage is limited only
  by the rating of external components
  such as the power MOSFET and the
  transformer. The LTC3805 can be
  programmed for frequency, slope
  compensation, soft-start, input voltage RUN/STOP thresholds (including …

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Manufacturer's Classification

• Power Management > Switching Regulator > Flyback, Forward and Isolated Controllers | SEPIC Regulators
• Power Management > Switching Regulator > Step-Up (Boost) Regulators > External Power Switch Boost
• Space & Harsh Environment > Extended Temperature Plastic (H & MP) > Extended Temperature (H & MP) Switching Regulators