ISL6144_14 Datasheet, PDF (14/30 Pages) Intersil Corporation – High Voltage ORing MOSFET Controller

ISL6144
Using the ISL6144EVAL1Z High Voltage
ORing MOSFET Controller Evaluation
Board
In a multiple supply, fault tolerant, redundant power
distribution system, paralleled power supplies contribute
equally to the load current through various power sharing
schemes. Regardless of the scheme, a common design
practice is to include discrete ORing power diodes to protect
against reverse current flow should one of the power
supplies develop a catastrophic output short to ground. In
addition, reverse current can occur if the current sharing
scheme fails and an individual power supply voltage falls
significantly below the others.
Although the discrete ORing diode solution has been used
for some time and is inexpensive to implement, it has some
drawbacks. The primary downside is the increased power
dissipation loss in the ORing diodes as power requirements
for systems increase. In some systems this lack of efficiency
results in a cost that surpasses the cost of the ISL6144 and
power FET implementation. The power loss across a typical
ORing diode with 20A is about 10W. Many diodes will be
paralleled to help distribute the heat. In comparison, a FET
with 5mΩ on-resistance dissipates 2W, which constitutes an
80% reduction. When multiplied by the number of paralleled
supplies, the power savings are significant. Another
disadvantage when using an ORing diode would be failure to
detect a shorted or open ORing diode, jeopardizing power
system reliability. An open diode reduces the system to a
single point of failure while a diode short might pose a
hazard to technical personnel servicing the system while
unaware of this failure.
The ISL6144 ORing MOSFET Controller and a suitably
sized N-Channel power MOSFET(s) increase power
distribution efficiency and availability when replacing a
power ORing diode in high current applications. It can be
used in +9V to +75V systems and has an internal charge
pump to provide a floating gate drive for the N-Channel
ORing MOSFET.
The input/output differential trip point “V_OUT - V_IN” can be
programmed by two external resistors (R₁, R₂ or R₆, R₇).
This trip point can be adjusted to avoid false gate trip off due
to power supply noise.
The high speed comparator action protects the common bus
from being affected due to individual power supply shorts by
turning off the ORing MOSFET of the shorted feed in less
than 300ns (when using an ORing MOSFET with equivalent
gate to source capacitance equal to 39nF).
The Hysteretic Regulating (HR) Amplifier provides a slow
turn-off of the ORing MOSFET. This turn-off is achieved in
less than 100µs when one of the sourcing power supplies is
shutdown slowly for system diagnostics, ensuring zero
reverse current. This slow turn-off mechanism also reacts to
output voltage droop, degradation, or power-down.
A circuit fault condition is indicated on an open drain FAULT
pin. The fault detection circuitry covers different types of
failures; including dead short in the sourcing supply, a
dead-short of any two ORing MOSFET terminals, or a blown
fuse in the power distribution path.
Typical Application
PS_1
VIN1
9V TO 75V
DC/DC
1 ^C5^*
V_PU
C1
R₃
LED1
CS
RED
Q₁
C₆*
VIN
GATE
R₁ C₂
U1 ^VOUT
ISL6144
HVREF
COMP
R₂
VSET
FAULT _GND
VOUT
PS_2
VIN2
9V TO 75V
DC/DC C₇*
2
V_PU
C₃
R₄
LED2
RED
Q₁
C₈*
GATE
R₆
VIN
U2 ^VOUT
ISL6144
C₄
HVREF
COMP
R₇
VSET
FAULT _GND
R₁ = R₆ = 499Ω (5%)
R₂ = R₇ = 47.5kΩ (5%)
R₃ = R₄ = 1.21kΩ (5%)
C₁ = C₂ = 150nF (10V)
C₃ = C₄ = 10nF (10V)
C₅* TO C₈* = 100nF *(100V) Optional Decoupling Caps
- LED1, LED2 are red LEDs to indicate a fault, different interfaces
are possible to the FAULT pin.
- V_PU is an external pull up voltage source. Also, V_OUT can be
used as the pull up source. In this case if it is higher than 16V,
use a zener diode from the FAULT pin to GND with a clamping
voltage less than the rating of the FAULT pin which is 16V.
Related Literature
• TB389 (PCB Land Pattern Design and Surface Mount
Guidelines for QFN (MLFP) Packages)
• Manufacturer’s MOSFET data sheets
14
FN9131.7
October 6, 2011