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Design Notes

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  Ideal Diodes Protect Against Power Supply Wiring Errors &mdash DN444
  PDF, 78 Kb, File published: Jun 10, 2008
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  Ideal Diodes Protect Against Power Supply Wiring Errors
  Design Note 444
  Meilissa Lum
  Introduction
  High availability systems often employ dual feed power
  distribution to achieve redundancy and enhance system
  reliability. ORing diodes join the feeds together at the
  point of load, most often using Schottky diodes for low
  loss. MOSFET-based ideal diodes can be used to replace
  Schottky diodes for a significant reduction in power
  dissipation, simplifying the thermal layout and improving
  system efficiency. Figure 1 shows the LTC4355 and
  LTC4354 combining the inputs and returns in a –48V, 5A
  dual feed application. This solution reduces the power
  dissipation from 6W using Schottky diodes to just 1.1W
  with MOSFETs.
  With two supply sources and four supply connections
  there are plenty of ways to incorrectly connect the wires.
  Although the likelihood of a wiring error is small, the cost
  is high if downstream cards are not designed to tolerate such errors. Wiring errors could include reverse polarity
  or cross-feed connections. Knowing this, circuit designers are accustomed to using discrete diode solutions to
  protect against such mishaps. It is important that active
  ideal diodes give similar protection. …

Articles

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  A Cool Circuit: 48V Ideal Diode-OR Reduces Heat Dissipation &mdash LT Journal
  PDF, 174 Kb, File published: Jun 14, 2007
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  L DESIGN FEATURES A Cool Circuit: 48V Ideal Diode-OR
  by Dan Eddleman
  Reduces Heat Dissipation
  Introduction
  High availability systems commonly
  demand redundant power supplies or
  backup battery feeds to enhance reliability. Traditionally, Schottky diodes
  were used to diode-OR these supplies
  at the point of load. However, as load
  currents climb, the forward voltage
  drop of the ORing diodes becomes a
  significant source of power loss. Designers are thus tasked with creating
  elaborate thermal layouts and heat
  sinks to contend with the diodes’ rising temperatures.
  A better solution for a high current,
  high availability system is to replace
  the Schottky diodes with MOSFETbased ideal diodes. This lowers the
  forward voltage drop of the diode-OR,
  shrinking thermal layouts and improving system power efficiency. The 4mm
  Г— 3mm LTC4355 simplifies the design
  of MOSFET ORing circuits by controlling two N-channel MOSFETs, which
  can combine supplies with voltages
  between 9V and 80V. The LTC4355 …

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  Ideal Diode Betters a Schottky by a Factor of Four in Power and Space Consumption &mdash LT Journal
  PDF, 501 Kb, File published: Jun 23, 2008
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  L DESIGN IDEAS Ideal Diode Betters a Schottky by a
  Factor of Four in Power and Space
  by Meilissa Lum
  Consumption
  Introduction
  High availability systems often use
  parallel power supplies or battery
  feeds to achieve redundancy and
  enhance system reliability. Traditionally, Schottky ORing diodes are used
  to connect these supplies at the point
  of load and prevent backfeeding into
  a faulty power supply. Unfortunately,
  the forward voltage drop of these diodes
  reduces the available supply voltage
  and dissipates significant power at
  high currents—costly heat sinks and
  elaborate layouts are needed to keep
  the diodes cool.
  When power dissipation is a
  concern, the Schottky diode can be
  replaced with a MOSFET-based ideal
  diode. This reduces the voltage drop
  and power dissipation, thereby reducing the complexity, size and cost of the …

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Manufacturer's Classification

• Monitor, Control and Protection > PowerPath Controllers & Ideal Diodes
• Space & Harsh Environment > Extended Temperature Plastic (H & MP) > Extended Temperature (H & MP) Power Management

Other Names:

LTC4355IDEPBF, LTC4355IDE PBF