ISL6144 Datasheet, PDF (20/29 Pages) Intersil Corporation – High Voltage ORing MOSFET Controller

ISL6144
Detection of Power Feed Faults
The ISL6144 have two built-in mechanisms that monitor
voltages at VIN, VOUT and GATE pins. The first mechanism
monitors GATE with respect to VIN (with a 410mV threshold)
and the second mechanism monitors V_IN with respect to VOUT
(with 370mV threshold). The open-drain FAULT pin will be
pulled low when any of the two above conditions is met.
Some of the typical system faults detected by the ISL6144 are:
Fault 1: Open Fuse at the Input Side
(Fuse has to be placed before the V_IN tap, between the
power supply and the source of the ORing MOSFET), note
that the EVAL board does not have footprint for installing this
fuse. This feature can be tested by adding a fuse externally.
The open fuse results in near zero current flow through the
ORing MOSFET, only a very low current drawn by the IC
bias will flow. The voltage at VIN pin is effectively
disconnected from the power source and will start dropping
slowly. The regulated source-drain voltage falls below its
20mV level and the gate of the MOSFET is pulled down and
turned off. GATE will become low and a fault is indicated with
internal built in delay (t_FLT).
Fault 2: Drain to Source Short
In this case V_IN is shorted to V_OUT, and in theory the voltage
drop across the shorted MOSFET terminals will be close to
0V. The Gate will be pulled down and a fault will be
indicated. The resistance of the Drain to Source short
multiplied by the Drain short current must be low enough to
result in V_SD< V_{FWD_HR} (refer to data sheet for worst case
values), Otherwise this fault cannot be detected.
V_IN = 12V, FAULT PULLED TO +5V
V_G1
5V/DIV
FAULT
5V/DIV
V_OUT
5V/DIV
V_IN1
5V/DIV
Fault 3: MOSFET Gate to Source Dead Short
GATE voltage will be equal to V_IN, GATE <V_IN + 0.37V and a
fault is indicated.
V_IN = 12V, FAULT PULLED TO +5V
V_G1
5V/DIV
FAULT
5V/DIV
V_OUT
5V/DIV
V_IN1
5V/DIV
TIME SCALE
100µs/DIV
FIGURE 27. MOSFET GATE TO SOURCE FAULT
Fault 4: ORing FET Off Condition
When V_IN < V_OUT, the Gate is off to block reverse current
flow. This means that if an ORing feed is not sharing current,
a fault will be indicated. Also if a feed (PS) is off while bias is
applied from V_OUT to that feed, then a fault is also indicated.
Fault 5: MOSFET Gate to Drain Dead Short
In this case, the following condition will be violated GATE
<V_IN + 0.37V and a fault is issued.
V_IN = 12V, FAULT PULLED TO +5V
V_G1
5V/DIV
FAULT
5V/DIV
V_OUT
5V/DIV
V_IN1
5V/DIV
TIME SCALE
100µs/DIV
FIGURE 26. MOSFET DRAIN TO SOURCE FAULT
TIME SCALE
100µs/DIV
FIGURE 28. MOSFET GATE TO DRAIN FAULT
20
FN9131.5
October 8, 2010