Datasheet
LTC4352
8
4352fa
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 with 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 resulting
power loss. Additionally, diodes provide no information
concerning the status of the sourcing supply. Separate
control must therefore be added to ensure that a supply
that is out of range is not allowed to affect the load.
The LTC4352 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.
Power Supply Configuration
The LTC4352 can operate with supplies down to 0V. This
requires powering the V
CC
pin with an always present
external supply in the 2.9V to 6V range. If not always
present, a series 470Ω resistor or Schottky diode limits
device power dissipation and backfeeding of low V
CC
supply when V
IN
is high. For a 2.9V to 4.7V V
CC
supply,
V
IN
should be lower than V
CC
. 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 V
IN
operates above 2.9V then the external supply at
V
CC
is not needed. The 0.1µF capacitor is still required
for bypassing.
applicaTions inForMaTion
Figure 1. 12V Ideal Diode with Status and Fault Indicators
V
CC
UV
OV
REV
LTC4352
STATUS
FAULT
0.1µF
C2
R4
2.7k
D1
D1: GREEN LED LN1351C
D2: RED LED LN1261CAL
MOSFET
ON
FAULT
D2
R5
2.7k
C1
TO LOAD
12V
Q1
Si7336ADP
0.1µF
4352 F01
CPO V
IN
SOURCE GATE
GND
OUT
Figure 2. Power Supply Configurations
V
CC
LTC4352
TO LOAD
0V TO V
CC
V
IN
GATE OUT
0.1µF
2.9V TO 4.7V
GND
V
CC
LTC4352
TO LOAD
0V TO 18V
4352 F02
V
IN
GATE OUT
GND
V
CC
LTC4352
TO LOAD
2.9V TO 18V
V
IN
GATE OUT
0.1µF
GND
0.1µF
4.7V TO 6V