Datasheet
LTC4353
8
4353f
High availability systems often employ parallel connected
power supplies or battery feeds to achieve redundancy
and enhance system reliability. ORing diodes have been
a popular means of connecting these supplies at the point
of load. Diodes followed by storage capacitors also hold
up supply voltages when an input voltage sags or has a
brownout. The disadvantage of these approaches is the
diode’s significant forward-voltage drop and the result-
ing power loss. The LTC4353 solves these problems by
using an external N-channel MOSFET as the pass element
(see Figure 1). The MOSFET is turned on when power is
being passed, allowing for a low voltage drop from the
supply to the load. When the input source voltage drops
below the output common supply voltage it turns off the
MOSFET, thereby matching the function and performance
of an ideal diode.
applicaTions inForMaTion
Figure 1. 12V Ideal Diode-OR with Status Lights
Figure 2. Power Supply Configurations
Power Supply Configuration
The LTC4353 can operate with input supplies down to 0V.
This requires powering the V
CC
pin with an early external
supply in the 2.9V to 6V range. In this range of operation
V
IN
should be lower than V
CC
. If V
CC
powers up after
V
IN
and backfeeding of V
CC
by the internal 5V LDO is a
concern, then a series resistor (few 100Ω) or Schottky
diode limits device power dissipation and backfeeding of
a low V
CC
supply when any V
IN
is high. A 0.1µF bypass
capacitor should also be connected between the V
CC
and
GND pins, close to the device. Figure 2 illustrates this.
If either V
IN
operates above 2.9V, the external supply at
V
CC
is not needed. The 0.1µF capacitor is still required
for bypassing.
GATE1
4353 F02
0V TO V
CC
0V TO
V
CC
V
IN1
V
CC
GATE2
V
IN2
LTC4353
2.9V TO 6V
GATE1
M1
M2
M1
M2
2.9V TO 18V
(0V TO 18V)
0V TO 18V
(2.9V TO 18V)
V
IN1
V
CC
GATE2
V
IN2
LTC4353
C
VCC
0.1µF
C
VCC
0.1µF
OPTIONAL
OR
HERE
M1
Si4126DY
M2
Si4126DY
GATE1CPO1
CPO2
GND
EN1
EN2
4353 F01
12V
12V
D1, D2: GREEN LED LN1351C
C
VCC
0.1µF
OUT
10A
C1
56nF
R1
2.7k
C2
56nF
V
IN1
V
CC
ONST1
ONST2
OUT1
OUT2
D1
D2
GATE2
V
IN2
LTC4353
R2
2.7k
C
L