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 fl ows backwards
through the LTC4358. When reverse current fl ows 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
amplifi er 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 fi rst 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
V
DD
OUTRTNA
V
INA
= 12V
12V BUS
LTC4358
GND
IN DRAIN
V
DD
OUT
PS2
RTNB
V
INB
= 12V
PS3
RTNC
V
INC
= 12V
4358 F01
LTC4358
GND
IN DRAIN
V
DD
OUT
Figure 1. Droop Sharing Redundant Supplies
