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Notas de Diseño

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  Tiny, Efficient High Power LED Camera Flash Solutions for Cell Phone Applications &mdash DN1009
  PDF, 69 Kb, Archivo publicado: oct 1, 2004
  Extracto del documento

  advertisement Tiny, Efficient High Power LED Camera Flash Solutions for
  Cell Phone Applications – Design Note 1009
  Keith Szolusha
  Introduction
  Cell phones and PDAs are approaching the limit for small
  form factors, but their feature sets are growing with new
  functions such as built-in cameras and even video cameras.
  The initial in-phone cameras were basic, low resolution devices with little in the way of usable flash capability. However, cell phone camera resolutions have improved and
  sophisticated flash technology is expected to keep pace.
  There are two flash technologies used in digital still cameras. The first uses a Xenon flash lamp to provide a very
  short, high lumen flash with excellent spectral characteristics. LTC offers Xenon photoflash solutions that are
  simple, compact and efficient (see Design Note 345).
  The second flash technology uses LEDs. LED solutions hold
  the upper hand when simplicity and space is at a premium
  and they are the only choice when �torch’ or video-mode
  lighting is required. LED flash units fit into spaces where
  even the smallest Xenon photoflash cannot. Until recently,
  LEDs could not compete with Xenon solutions in light
  output and spectral performance, relegating them to the
  realm of low resolution (sub 1 megapixel) cameras. However, recent (>10Г—) performance improvements have made LEDs an attractive solution for the now popular 1 megapixel
  and higher cell phone cameras.
  Linear Technology offers many simple and extremely
  compact solutions for driving the latest high-light-output LEDs, including Lumileds Luxeon Flash LEDs. These …

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  Current-Limited DC/DC Converter Simplifies USB Power Supplies &mdash DN252
  PDF, 91 Kb, Archivo publicado: marzo 2, 2001
  Extracto del documento

  advertisement Current-Limited DC/DC Converter Simplifies USB
  Power Supplies – Design Note 252
  Bryan Legates
  Many portable universal serial bus (USB) devices power
  themselves from the USB host or hub power supply
  when plugged into the USB port. Several requirements
  must be met to ensure the integrity of the bus: the
  USB specification dictates that the input capacitance
  of a device must be less than 10ОјF to minimize inrush
  currents when the device is plugged into the USB port;
  when п¬Ѓrst plugged in, the device must draw less than
  100mA from the port, and for high power devices, the
  current drawn from the port can increase to 500mA
  only after it is given permission to do so by the USB
  controller. These requirements can be easily met using
  the LT1В®618 DC/DC converter, which provides an accurate input current control ideal for USB applications.
  The LT1618 combines a traditional voltage feedback
  loop with a unique current feedback loop to operate as
  a constant-current, constant-voltage source.
  USB to 12V Boost Converter
  Figure 1 shows a 5V to 12V boost converter ideal
  for USB applications. The converter has a selectable
  100mA/500mA input current limit, allowing the device to …

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  DC/DC Converter Drives Lumileds White LEDs from a Variety of Power Sources &mdash DN340
  PDF, 76 Kb, Archivo publicado: jun 2, 2004
  Extracto del documento

  DC/DC Converter Drives White LEDs from a
  Variety of Power Sources – Design Note 340
  Keith Szolusha
  Introduction
  LEDs are usually driven with a constant DC current
  source in order to maintain constant luminosity. However, most DC/DC converters are designed to deliver
  a constant voltage by comparing a feedback voltage
  to an internal reference via an internal error amplifier.
  The easiest way to turn a simple DC/DC converter into
  a constant current source is to use a sense resistor to
  turn the output current into a voltage and use it as the
  feedback. The problem with this method is its reduced
  efficiency—700mA across a 1.2V (typical reference voltage) drop produces an 840mW power loss. One solution
  is to use an external op amp to amplify the voltage of a
  low value resistor to the given reference voltage. This
  saves converter efficiency, but significantly increases
  the cost and complexity of a simple converter with the
  additional components and board space.
  A superior solution is to use the LTВ®1618 constant
  current, constant voltage converter, which combines
  a traditional voltage feedback loop and a unique current feedback loop to operate as a constant-voltage,
  constant-current DC/DC converter. No external op amps
  are required for this extremely compact solution. The …

Artículos

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  Current-Limited DC/DC Converter Simplifies USB Power Supplies &mdash LT Journal
  PDF, 177 Kb, Archivo publicado: feb 1, 2001
  Extracto del documento

  DESIGN FEATURES Current-Limited DC/DC Converter
  Simplifies USB Power Supplies
  by Bryan Legates
  Introduction
  currents when the device is plugged
  into the USB port; when first plugged
  in, the device must draw less than
  100mA from the port and, for high
  power devices, the current drawn from
  the port can increase to 500mA only
  after it is given permission to do so by
  the USB controller. These requirements can be easily met using the Many portable Universal Serial Bus
  (USB) devices power themselves from
  the USB host or hub power supply
  when plugged into the USB port. Several requirements must be met to
  ensure the integrity of the bus: the
  USB specification dictates that the
  input capacitance of a device must be
  less than 10ВµF to minimize inrush
  L1
  10ВµH C1
  4.7ВµF 3 VOUT
  12V 2 7 ISN SW R1 …

Linea modelo

Clasificación del fabricante

• Power Management > Switching Regulator > LCD/CCD/OLED Bias | SEPIC Regulators
• Power Management > Switching Regulator > Step-Up (Boost) Regulators > Internal Power Switch Boost
• Power Management > LED Driver ICs > Step-Up (Boost) LED Drivers | Step-Down (Buck) LED Drivers | Buck-Boost LED Drivers