LINEAR DESIGN FEATURES LTMag-V18N02-14-LTC4355_57 - Meilissa Lum User Manual, Technical Guide

L DESIGN IDEAS

CU RR EN (A

Ideal Diode Betters a Schottky by a Factor of Four in Power and Space

Consumption by Meilissa Lum

Introduction High availability systems often use

parallel power supplies or battery IN DRAIN

VIN = 12V VOUT TO 5A LOAD

feeds to achieve redundancy and

enhance system reliability. Tradition-

LTC4358 VDD

ally, 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

Figure 1. No external components are needed for a 12V/5A ideal diode.

reduces the available supply voltage and dissipates significant power at high currents—costly heat sinks and and LTC4358 enable MOSFET-based elaborate layouts are needed to keep ideal diode solutions for various ap-

With one-fourth the

the diodes cool. plications—the choice depends on the

When power dissipation is a dissipated power, system current and operating voltage of the

concern, the Schottky diode can be application. Table 1 compares these

efficiency is increased and

replaced with a MOSFET-based ideal devices.

diode. This reduces the voltage drop PCB layout is simplified—no

and power dissipation, thereby reduc- Ideal Diode Easier to Use

need for costly and bulky

ing the complexity, size and cost of the Than a Schottky

PO ER IS SI PA TI ON (W heat sinks.

thermal layout and increasing system Of particular interest is the LTC4358, efficiency. The LTC4355, LTC4357 which includes an internal 20mΩ

DIODE (B530C) 1.5

DIODE (B530C)

FET (LTC4358)

POWER SAVED

FET (LTC4358)

VOLTAGE DROP (m V) CURRENT (A)

Figure 2. The LTC4358 ideal diode takes on a 5A B530C Schottky diode. The LTC4358 easily wins in voltage drop, power loss and package size.

Table 1. Comparison of ideal diode parts

Part Number Description Operating Voltage Configuration Package

Positive Voltage Diode-OR 9V–80V,

LTC4355 Dual, External MOSFETs DFN14 (4mm × 3mm), SO16

Controller and Monitor 100V Abs Max Single Positive Voltage 9V–80V,

LTC4357 Single, External MOSFET DFN6 (2mm × 3mm), MSOP8

Ideal Diode Controller 100V Abs Max

LTC4358 Ideal Diode 5A Internal MOSFET DFN14 (4mm × 3mm), TSSOP16

28V Abs Max

Linear Technology Magazine • June 2008