ISL6144 Intersil Corporation, ISL6144 Datasheet - Page 24

• Manufacturer Part Number: ISL6144
• Description: High Voltage ORing MOSFET Controller
• Manufacturer: Intersil Corporation

Configuring ISL6144 for Backup
Redundancy (Rail Selector)
The ISL6144 can be used as a rail selector in applications
with backup redundancy. In this case, the backup power
source voltage (for example battery) should be selected in
such a manner that it is lower than the prime source voltage.
Prime_PS > Backup_PS
Also, the voltage difference between the two rails has to be
higher than the High Speed Comparator threshold voltage.
Prime_PS - Backup_PS >> V
(BY INCREASING
INCREASE
V
R1 ONLY)
TH(HS)
FIGURE 32. SELECTING V
NO
USE CURRENT VALUES of R
TH(HS)
24
CURRENT SHARING MODE
COMPARE GATE-SOURCE
OPERATE ALL FEEDS IN
(V
V
SET V
GS1
IN1
AND V
R
= V
VOLTAGES
R
≅ V
TH(HS)
2
TH(HS)
n = N+1
START
1
= 47.5kΩ
STOP
IN2
= 499Ω
GS2
TH(HS)
=...= V
YES
≅...V
= 55mV
VALUE
GSn
INn
)
1
ISL6144
Remote Sense in Redundant Power
Systems
Remote output voltage sensing is a feature implemented in
most of today’s power supplies. This feature is used to
compensate for any resistive voltage drops between the
power supply output and the load-connection point. The
remote sensing pin (RS/+S) must be connected as close as
possible to the load in order to compensate for any resistive
voltage drops across the power path from the power supply
output to the load. The output of many such power supplies
can be connected in parallel to provide redundancy and fault
tolerance. An ORing device (MOSFET/Diode) is typically
used to provide the required isolation of any fault on the
power supply side from propagating to the load side. In this
case it is not recommended to connect the remote sense
pins of the parallel units to the Common Bus point (at load
terminals), as this can provide an alternative path for fault
currents. The remote sense pins can be connected on the
input side of the ORing device to compensate for any drop
prior to it. Using an ORing MOSFET (compared to an ORing
diode) reduces the forward voltage drop. By using a low
r
systems, the forward voltage drop can be reduced to less
than 100mV. This is another advantage over the ORing
diode solution (that has 400mV to 600mV drop) when tight
regulation is imposed on the Common Bus voltage. If remote
sense is absolutely required, one has to make sure that it will
not lead to fault propagation when one power supply output
is shorted. The remote sense configuration has to be looked
at and design precautions has to be made to make sure the
redundancy and fault tolerance are not compromised by the
remote sense connection to the Common Bus.
DS(ON)
FIGURE 33. USING ISL6144 FOR BACKUP REDUNDANCY
BACKUP_PS
PRIME_PS
RED
N-Channel ORing MOSFET in redundant power
RED
R
R
C
C
4
3
7
5
*
5V
5V
*
LED2
LED1
C
C
3
1
VIN
HVREF
FAULT
VIN
HVREF
FAULT
ISL6144
ISL6144
GATE
GATE
GND
GND
Q
Q
COMP
1
COMP
VOUT
2
VOUT
VSET
VSET
R
R
6
1
C
C
R
R
6
8
7
2
*
*
C
C
2
February 15, 2007
4
VOUT
FN9131.3