PI2126 Datasheet, PDF (5/15 Pages) Vicor Corporation – 30 Volt, 12 Amp Full-Function Active ORing Solution

EOL
Functional Description:
The PI2126 integrated Cool-ORing product takes
advantage of two different technologies combining a
4.5m on-state resistance (R_DS(on)) N-channel MOSFET
with high density control circuitry. This combination
provides superior density, minimizing PCB space to
achieve an ideal ORing diode function, significantly
reducing power dissipation and eliminating the need for
heat sinking, while minimizing design complexity.
The PI2126’s 4.5mΩ on-state resistance MOSFET used in
the conduction path enables a dramatic reduction in
power dissipation versus the performance of a diode
used in conventional ORing applications due to its high
forward voltage drop.
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 directions. 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.
Differential Amplifier:
The PI2126 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 the Reverse and Forward comparators.
Reverse Current Comparator: RVS
The reverse current comparator provides the 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 force
the gate discharge circuit to turn off the MOSFET in
typically 90ns and assert the Fault ( ) low with a typical
delay of 8μs to report a fault condition.
The reverse comparator will hold the gate low until the
SP pin is 6mV higher than the SN pin. Reverse
comparator hysteresis is shown in Figure 3.
Figure 3: Reverse comparator hysteresis, the hysteresis
voltage is SP-SN
Forward Voltage Comparator: FWD
The FWD comparator detects when a forward voltage
condition exists and SP is above 275mV (typical) positive
with respect to SN. When SP-SN is more than 275mV, the
FWD comparator will assert the Fault ( ) low to report a
fault condition.
VC and Internal Voltage Regulator:
The PI2126 has a separate input VC that provides power
to the control circuitry. An internal regulator clamps the
VC voltage with respect to PG pin (V_VC-PG) to 11.7V
typical.
The internal regulator circuit has a comparator to
monitor VC voltage and pulls the MOSFET Gate low when
VC is lower than the VC Under-Voltage Threshold.
The VR input pin can be connected to the input voltage
eliminating the need for an external limiter in 12V Bus
applications (10V to 14V). An internal 420Ω resistor is
connected between the VR pin and the internal regulator
VC pin.
Fault Indication:
The pin is an open collector NPN that will be pulled
low under the following fault conditions.
Typical Condition
1 Reverse: V_SP-V_SN ≤ -6mV
2 Forward: V_SP-V_SN ≥ +275mV
3 Forward V_SP-V_SN ≤ +6mV
4 UVLO
4.5V < V_VC-PG <7.15V
Indication of possible faults
Input supply shorted
(MOSFET turned OFF)
Open FET, Gate short or
open, High current
(MOSFET turned ON)
Shorted FET on power-up
(MOSFET turned OFF)
Controller not ready
(MOSFET turned OFF)
Picor Corporation • picorpower.com
PI2126
Rev 1.1
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