PI2001 Datasheet, PDF (13/23 Pages) Vicor Corporation – Universal Active ORing Controller IC

Application Information:
The PI2001 is designed to replace ORing diodes in
high current redundant power architectures.
Replacing a traditional diode with a PI2001 controller
IC and a low on-state resistance N-channel MOSFET
will result in significant power dissipation reduction as
well as board space reduction, efficiency improvement
and additional protection features. This section
describes in detail the procedure to follow when
designing with the PI2001 Active ORing controller and
N-Channel MOSFETs. Three different Active ORing
design examples are presented.
Fault Indication:
FT output pin is an open collector and should be
pulled up to the logic voltage or to the controller VC
via a resistor (10KΩ)
Blanking Timer:
Connect the blanking timer pin (BK) to GND to
program the device for the fastest reverse comparator
response time of 160ns typical. To increase the
blanking time, connect the BK pin to GND via a
resistor to avoid the fault response to short reverse
current pulses. Refer to Figure 2 in the reverse
comparator functional description for resistor values
versus the reverse blanking time.
Auxiliary Power Supply (Vaux):
Vaux is an independent power source required to
supply power to the PI2001 VC input. The Vaux
voltage should be higher than Vin (redundant power
source output voltage) by the required gate-to-source
voltage (Vgs) to fully enhance the MOSFET, plus 0.5V
maximum gate to VC headroom (VHD_VC-G)
Vaux = Vin + Vgs + VHD_VC-G
Where, VHD_VC-G is defined as the 0.5V maximum drop
from VC in the Gate Voltage High (V_G) specification in
the Gate Driver section of the Electrical Specification.
For example, if the bus voltage is 3.3V and the
MOSFET requires 5.0V of Vgs to fully enhance the
MOSFET, then Vaux should be at least 3.3V + 5.0V +
0.5V = 8.8V.
If Vaux is higher than 15V then a bias resistor (Rbias)
is required, and should be connected between the
PI2001 VC pin and Vaux. The resistor is selected
based on the input voltage range.
Minimize the resistor value for low Vaux voltage levels
to avoid a voltage drop that may reduce the VC
voltage lower than required to drive the gate of the
MOSFET. Select the value of Rbias using the
following equations:
Rbias = ^{Vauxmin − VCclamp}
IC _max
Rbias maximum power dissipation:
Pd _Rbias
=
(Vaux_max −VC_clamp ) ²
Rbias
Rbias maximum power dissipation is at maximum
input voltage and minimum clamp voltage (15V).
Where:
Vaux_min : Vaux minimum voltage
Vaux_max : Vaux maximum voltage
VC_Clamp : Controller clamp voltage, 15.5V
IC_max : Controller maximum bias current (4.2mA)
Slave:
For a high current application where one MOSFET
can not handle the total load current, multiple
MOSFETs can be paralleled and driven by a single
PI2001 controller. Special care has to be taken when
multiple MOSFET gates are driven from one gate
driver output. The gate driver output capability will be
divided by the number of MOSFET gates connected
to it and will slow the MOSFET response to a reverse
fault. To avoid MOSFET slow response the PI2001
can be configured in a master / slave configuration
providing localized gate drive to each paralleled
MOSFET.
The PI2001 slave feature allows the user to parallel
multiple PI2001s and configure one unit as the master
and the rest in slave mode. The slave ( SL ) pin of the
master unit will act as an output driving the units
configured in slave mode. The SL pins of the slaved
units will act as inputs under the control of the master.
In this configuration each MOSFET will have its own
localized gate driver which is synchronized by the
master controller, thereby improving the response to a
reverse current condition. One master controller is
capable of driving up to 10 slave inputs.
N-Channel MOSFET Selection:
There are several factors that affect the MOSFET
selection including cost, on-state resistance (Rds(on)),
current rating, power dissipation, thermal conductivity,
drain-to-source breakdown voltage (BVdss), gate-to-
source voltage rating (Vgs), and gate threshold
voltage (Vgs_(TH)).
The first step is to select suitable MOSFETs based on
the BVdss requirement for the application. The BVdss
voltage rating should be higher than the applied Vin
voltage plus expected transient voltages. Stray
parasitic inductance in the circuit can also contribute
to significant transient voltage conditions, particularly
Picor Corporation • picorpower.com
PI2001
Rev 1.0 Page 13 of 23