PI2001 datasheet(13/23 Pages) VICOR

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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 (VHDVC-G)

Vaux = Vin + Vgs + VHDVC-G

Where, VHDVC-G is defined as the 0.5V maximum drop

from VC in the Gate Voltage High (VG) 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:

max

min

Vaux

Rbias

clamp

−

Rbias maximum power dissipation:

Rbias

Vaux

clamp

Rbias

max

)

(

−

Rbias maximum power dissipation is at maximum

input voltage and minimum clamp voltage (15V).

Where:

min

Vaux

: Vaux minimum voltage

max

Vaux

: Vaux maximum voltage

Clamp

: Controller clamp voltage, 15.5V

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

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