Datasheet Linear Technology LTC4354

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Design Notes

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  Replace ORing Diodes with MOSFETs to Reduce Heat and Save Space &mdash DN363
  PDF, 72 Kb, File published: Mar 25, 2005
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  Replace ORing Diodes with MOSFETs to Reduce Heat
  and Save Space – Design Note 363
  James Herr and Mitchell Lee The LTC В®4354 negative voltage diode-OR controller
  realizes near-ideal diode behavior. External N-channel
  MOSFETs, actively driven by the LTC4354, act as pass
  transistors to replace the diodes. The device maintains a small 30mV forward voltage drop across the
  MOSFETs at light load; under heavy load the voltage
  drop becomes a function of RDS(ON). For example, an
  18mО© MOSFET and 5A load current produce a drop of
  90mV, representing a more than п¬Ѓve fold improvement
  in drop and power dissipation over a Schottky diode,
  which exhibits 500mV drop under the same operating
  conditions. Lower power dissipation conserves board
  space and saves the cost of heat sinks. At the same
  time, 410mV of input operating range is added—a
  critical factor when the system is running on hold-up
  capacitors with only a few volts of headroom.
  Ideal –48V ORing Diode
  Figure 1 shows a comparison of power dissipation for a
  diode and a MOSFET driven by the LTC4354. At 10A, the
  voltage drop across a 100V Schottky diode (MBR10100)
  is around 620mV; a heat sink is required to handle resulting 6.2W of power dissipation. Using an LTC4354
  driving a 100V N-channel MOSFET (IRFR3710Z), the …

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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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  Replace -48V ORing Diodes with FETs to Reduce Heat and Save Space &mdash LT Journal
  PDF, 138 Kb, File published: Mar 25, 2005
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  DESIGN FEATURES Replace –48V ORing Diodes with FETs
  to Reduce Heat and Save Space by James Herr Introduction
  5
  DIODE (MBR10100) 4
  3 POWER
  SAVED 2
  1
  0 FET (IRFS4710) 0 2 4
  6
  CURRENT (A) 8 10 Figure 1. FET-based diode circuit saves power through an external current limiting
  resistor (RIN). An internal shunt regulator clamps the voltage at the VCC
  pin to 11V above VSS. At power-up,
  the initial load current flows through
  –48V_RTN RIN
  12k
  0.5W 26 R3
  33k 3
  VCC LTC4354
  DA DB 1
  R1
  2k VA 8
  R2
  2k FAULT 4 7 VSS GB GA TO …

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  Negative Voltage Diode-OR Controller Tolerates Inputs to 300V and Beyond &mdash LT Journal
  PDF, 1.7 Mb, File published: Jan 20, 2012
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  Negative Voltage Diode-OR Controller Tolerates Inputs to
  300V and Beyond
  Mitchell Lee The LTC4354 negative
  voltage diode-OR controller
  is designed to operate
  with inputs of up to 100V.
  As shown in Figure 1,
  the maximum voltage
  between –48V, VA and
  –48V, VB is limited to 100V,
  and the voltage applied
  to either input is similarly
  limited to 100V relative to
  –48COM. A careful study
  of the LTC4354 data sheet
  reveals that the drain pins,
  DA and DB, which are the
  only pins exposed to high
  voltage, are limited to 80V.
  Nevertheless, with a 2k
  series limiting resistor, these
  pins can handle up to 100V. Figure 1. The LTC4354 shown in a
  10A,–48V application handles up to …

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Manufacturer's Classification

• Monitor, Control and Protection > PowerPath Controllers & Ideal Diodes