ISL6144 Datasheet, PDF (24/29 Pages) Intersil Corporation – High Voltage ORing MOSFET Controller

ISL6144
START
SET V_TH(HS) = 55mV
R₁ = 499Ω
R₂ = 47.5kΩ
OPERATE ALL FEEDS IN
CURRENT SHARING MODE
(V_IN1 = V_IN2 =...= V_INn)
n = N+1
INCREASE
NO
V_TH(HS)
(BY INCREASING
R1 ONLY)
COMPARE GATE-SOURCE
VOLTAGES
V_GS1 ≅ V_GS2 ≅...V_GSn
YES
STOP
USE CURRENT VALUES of R₁
AND V_TH(HS)
FIGURE 31. SELECTING V_TH(HS) VALUE
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_TH(HS)
PRIME_PS
Q₁
C₅*
5V
C₁
R₃
LED1
RED
C₆*
GATE
VIN
VOUT
ISL6144
R₁
HVREF
COMP
FAULT
VSET
GND
C₂
R₂
VOUT
BACKUP_PS
Q₂
C₇*
5V _C3
R₄
LED2
RED
GATE
VIN
VOUT
ISL6144
R₆
HVREF
COMP
FAULT
VSET
GND
C₈*
C₄
R₇
FIGURE 32. USING ISL6144 FOR BACKUP REDUNDANCY
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_DS(ON) N-Channel ORing MOSFET in redundant power
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.
24
FN9131.5
October 8, 2010