PI2001 Datasheet, PDF (6/23 Pages) Vicor Corporation – Universal Active ORing Controller IC

Functional Description:
The PI2001 Cool-ORing controller IC is designed to
drive single or paralleled N-channel MOSFETs in
Active ORing applications. The PI2001 used with an
external MOSFET can function as an ideal ORing
diode in the high or low side of a redundant power
system, significantly reducing power dissipation and
eliminating the need for heatsinking.
An N-channel MOSFET in the conduction path offers
extremely low on-resistance resulting in a dramatic
reduction of power dissipation versus the
performance of a diode used in conventional ORing
applications due to its high forward voltage drop.
This can allow for the elimination of complex heat
sinking and other thermal management
requirements. Due to the inherent characteristics of
the MOSFET, while the gate remains enhanced
above the gate threshold voltage it will allow current
to flow in the forward and reverse direction. Ideal
ORing applications do not allow for reverse current
flow, so the controller has to be capable of very fast
and accurate detection of reverse current caused by
input power source failures, and turn off the gate of
the MOSFET as quickly as possible. Once the gate
voltage falls below the gate threshold, the MOSFET
is off and the body diode will be reverse biased
preventing reverse current flow and subsequent
excessive voltage droop on the redundant bus.
During forward over-current conditions caused by
load faults, the controller maintains gate drive to the
MOSFET to keep power dissipation as low as
possible, otherwise the inherent body diode of the
MOSFET would conduct, which has higher effective
forward drop. Conventional ORing solutions using
diodes offer no protection against forward over-
current conditions. During the forward over-current
condition, the PI2001 will provide an active-low fault
flag to the system via the FT pin. The fault flag is
also issued during the reverse current condition,
light load conditions, VC Under-Voltage, Input
Under-Voltage and Over-Voltage and Over-
Temperature conditions.
Differential Amplifier:
The PI2001 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 Comparator: RVS
The reverse comparator is the most critical
comparator. It looks for negative voltage caused by
reverse current. When the SN pin is 6mV higher
than the SP pin, the reverse comparator will enable
the BK current source to charge an internal 2pF
capacitor. The blanking timer provides noise filtering
for typical switching power conversion that might
cause premature reverse current detection. Once
the voltage across the capacitor reaches the timer
threshold voltage (1.25V) the gate will be discharged
by a 4Apk current. The shortest blanking time is
50ns when BK is connected to ground. The
Blanking time programmed by the BK pin will be
added to the controller delay time. The Electrical
Specifications in the DIFFERENTIAL AMPLIFIER
AND COMPARATOR section for Reverse Fault to
Slave Low Delay Time “t_RVS-MS or t_RVS-SL” is the
controller delay time plus the blanking time.
Reverse Blanking Timer: BK
Connecting an external resistor ( R_BK ) between the
BK pin and ground will increase the blanking time as
shown in Figure 2.
Where: R_BK ≤ 200KΩ
If BK is connected to VC for slave mode operation,
then the blanking time will be about 320ns typically,
and total delay time will be 430ns.
The reverse comparator has 3mV of hysteresis
referenced to SP-SN.
If the conditions are met for a reverse current fault,
then the active-low fault flag output will also indicate
a fault to the system after the 40µs fault delay time.
Figure 2: Blanking time vs. BK resistor value
Picor Corporation • picorpower.com
PI2001
Rev 1.0 Page 6 of 23