PI2122 datasheet(13/19 Pages) VICOR

13 / 19 page

Application Information:

The PI2122 is designed to replace ORing diodes

and load disconnect switchs in high current

redundant power architectures.

Replacing a

traditional diode with a PI2122 will result in

significant power dissipation reduction as well as

board space reduction, efficiency improvement,

input power source and output protection plus

additional

protection

features.

This

section

describes in detail the procedure to follow when

designing with the PI2122 Active ORing solution. A

design example is presented for Active ORing with

load disconnect.

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)

Over-Current Timer: OCT

Connect a capacitor, in the range of 1nF to 20nF to

set the off time after over-current shutdown (see

Figure 4).

Short Circuit Detect: SCD

Connect SCD pin to VC to avoid high inrush current

into a capacitive load, or connect SCD to GND pin

for fast turn on. The internal MOSFETs gate drive

current has two levels based on the SCD voltage

level.

Auxiliary Power Supply (Vaux):

Vaux is an independent power source required to

supply power to the VC input. The Vaux voltage

should be 4V higher than Vin (redundant power

source output voltage) to fully enhance the internal

MOSFETs.

A bias resistor (Rbias) is required if the bias supply

(Vaux) is higher than 15V.

Rbias should be

connected between the VC pin and Vaux to limit the

current into the internal shunt regulator.

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 internal MOSFETs.

Select the value of Rbias using the following

equations:

max

min

Vaux

Rbias

clamp

−

Rbias maximum power dissipation:

Rbias

Vaux

clamp

Rbias

max

)

(

−

Where:

min

Vaux

: Vaux minimum voltage

max

Vaux

: Vaux maximum voltage

Clamp

: Controller clamp voltage, 15.5V

max

: Controller maximum bias current, use

4.2mA

Example: Vaux 20V to 30V

−

Vaux

Rbias

clamp

max

min

Rbias

Vaux

clamp

Rbias

196

)

(

)

(

max

−

Internal N-Channel MOSFET BVdss:

In an application when the MOSFETs are turned off

due to a fault, the series parasitic elements in the

circuit may contribute to the MOSFET being exposed

to a voltage higher than its voltage rating.

It is

critical to follow best layout practice to minimize

parasitic inductance in the PCB layout especially in

the high current path.

In Active ORing applications when one of the input

power sources is shorted, a large reverse current is

sourced from the circuit output through the

MOSFETs. Depending on the output impedance of

the system, the reverse current may reach over 60A

in some conditions before the MOSFET is turned off.

Such high current conditions will store energy even

in a small parasitic element. For example: a 1nH

parasitic inductance with 60A reverse current will

generate 1.8µJ (½Li

2). When the MOSFETs are

turned off, the stored energy will be released and

produce a high negative voltage ringing at D1. At

the same time the energy stored at D2 of the internal

MOSFETs will be released and produce a voltage

higher than the load voltage. This event will create a

high voltage difference between the drain and

source of the MOSFET. To reduce the magnitude of

the ringing voltage, add a ceramic capacitor very

close to D1 that can react to the voltage ringing

frequency and another capacitor close to D2.

Recommended values for the ceramic capacitors are

1µF; refer to C5 and C7 in Figure 24.

Note:

Since the two MOSFETs are connected in to back-

to-back configuration, the maximum breakdown

voltage is BVdss of one MOSFET plus one diode

forward voltage

OV and UV resistor selection:

The UV and OV comparator inputs are used to

monitor the input voltage and will indicate a fault

condition when this voltage is out of range. The UV

and OV pins can be configured in two different ways,

either with a divider on each pin, or with a three-

resistor divider to the same node, enabling the

Picor Corporation • picorpower.com

PI2122

Rev1.0

Page 13 of 19

PI2122 Datasheet(PDF) 13 Page - Vicor Corporation

PI2122 Datasheet(HTML) 13 Page - Vicor Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Datasheet Download

Link URL