PI2002 Datasheet, PDF (6/23 Pages) Vicor Corporation – Active ORing Controller IC with Load Disconnect Feature

Functional Description:
The PI2002 controller IC product is designed to drive
back-to-back N-channel MOSFETs in Active ORing
applications that also require a load disconnect
feature. The PI2002 used with external back-to-
back MOSFETs can function as an ideal ORing
diode in the high-side of a redundant power system
coupled with a load disconnect switch, significantly
reducing power dissipation and eliminating the need
for heatsinking.
The PI2002 provides the ability to block current in
both directions by driving two MOSFETs in a back-
to-back configuration as shown in Figure 1a. This
configuration offers the ability to protect the load and
the MOSFET, by pulling the gate low, during
Reverse Current, Forward Over-Current, Under-
Voltage, Over-Voltage and Over-Temperature faults.
The fault flag is also issued during these fault
conditions.
Differential Amplifier:
The PI2002 integrates a high-speed low offset
voltage differential amplifier to sense the difference
between the Sense Positive (SP) pin voltage and
Sense Negative (SN) pin voltage with high accuracy.
The amplifier output is connected to three
comparators: Reverse comparator, Forward
comparator, and Forward over-current comparator.
Reverse Current Comparator: RVS
The reverse current comparator provides the most
critical function in the controller, detecting negative
voltage caused by reverse current. When the SN
pin is 6mV higher than the SP pin, the reverse
comparator will enable the gate discharge circuit and
turn off the MOSFETs in typically 120ns.
The reverse comparator has typically 3mV of
hysteresis referenced to SP-SN.
Forward Current Comparator: FWD
The FWD comparator detects when a forward
current condition exists and SP is 5mV (typical)
positive with respect to SN. When SP-SN is less
than 5mV it will indicate a fault condition on the
FT pin during a light load while maintaining gate
drive to the MOSFETs. The PI2002 will initiate a
gate shutdown if the Forward “AND” the over-voltage
(OV) condition are true.
Forward Over-Current Comparator: FOC
The FOC comparator indicates an excessive forward
current condition when SP is 112mV higher than SN.
The PI2002 controller will initiate a fault condition
when the GATE output voltage is more than 45% of
the regulated gate to SN voltage and SP-SN is
higher than 112mV, the MOSFETs will turn off then
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retry after a controlled off-time determined by the
capacitor value on the OCT input pins.
Over-Current Timer: OCT
OCT off-time is set by the OCT a capacitor as shown
in Figure 3.
The OCT block will control the off-time of the
MOSFETs after a FOC fault condition has occurred.
The equivalent block diagram is shown in Figure 2.
As the Set input at the OCT timer goes high, Out
will go low, pulling the GATE pin low. At the same
time a one shot of 40µs discharges the OCT
capacitor, then releases it charging the capacitor
again. Out and GATE pins stay low until the OCT
pin reaches the OCT high threshold (V_OCT-Hi), then
Out goes high and the GATE pin sources current to
charge the MOSFET gates. As soon as the GATE
voltage reaches 45% of the GATE to SN clamp
voltage, or 45% of {VC-V(SN) -0.25V}, the Clamp
Detector asserts a low signal again at the NOR gate.
If FOC is still low then the GATE pin will be pulled
low and will start a new off-time cycle of the Over-
Current timer.
Figure 2: OCT block and timing diagram
PI2002
Rev1.1 Page 6 of 23