LTC4358

7

4358fa

APPLICATIONS INFORMATION

ORing Two Supply Outputs

Where LTC4358s are used to combine the outputs of two

supplies, the power supply with the highest output voltage

sources most or all of the current. If this supply’s output

is quickly shorted to ground while delivering load current,

the current temporarily reverses and flows backwards

through the LTC4358. When reverse current flows the

LTC4358 ideal diode is quickly turned off.

If the other initially lower supply was not delivering load

current at the time of the fault, the output falls until the

LTC4358 body diode conducts. Meanwhile, the internal

amplifier turns on the MOSFET until the forward drop is

reduced to 25mV. If instead this supply was delivering

load current at the time of the fault, its ORing MOSFET

was already driven at least partially on, and will be driven

harder in an effort to maintain a drop of 25mV.

Load Sharing

Figure 1 combines the outputs of multiple, redundant

supplies using a simple technique known as droop sharing.

Load current is first taken from the highest output, with the

low outputs contributing as the output voltage falls under

increased loading. The 25mV regulation technique ensures

smooth load sharing between outputs without oscillation.

The degree of sharing depends on the 20mΩ resistance

of the LTC4358 internal MOSFET, the output impedance

of the supplies and their initial output voltages.

LTC4358

GND

IN

PS1

DRAIN

OUT

RTNA

12V BUS

LTC4358

GND

IN

DRAIN

OUT

PS2

RTNB

PS3

RTNC

4358 F01

LTC4358

GND

IN

DRAIN

OUT

Figure 1. Droop Sharing Redundant Supplies