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Application Notes

PT4481

Configuring PT4481 DC/DC Converters

for N+1 Operation

‘N+1’ vs OR’ing

The PT4481 DC/DC converter modules may be

operated with other PT4481 modules in ‘N+1’

configurations. A simple OR’ing connection allows

a number of converters to share the load current. An

‘N+1’ configuration adds redundancy by employing

at least one more converter than is necessary to

supply the load. This ensures that upon the loss of

one converter, sufficient capacity remains to supply

the load without interruption. As an example, a 45-A

load configured for ‘N+1’ would require no less than

three PT4481 converters. Two are needed to meet

the load demand, plus one additional converter to

ensure redundancy. Figure 1-1 shows the schematic

for operating two PT4481 converters in an ‘N+1’

configuration for a 25-A load application.

Blocking Diodes

A true ‘N+1’ redundant system must also protect the

output bus against fault current back-feeding a con-

verter. Without a blocking diode, a converter will sink

current as a result of a fault at its output, or due to the

PT4481

PT4481

1

2

8–13

20

7

REMOTE SENSE (+)

REMOTE SENSE (–)

PROGRAMMING PINS

3

C

(Required)

+

18–13

14–19

25

24

23

22

21

14–19

2

626

20

626

7

REMOTE SENSE (+)

21

22

23

24

25

3

PROGRAMMING PINS

D

(Required)

–V

IN

+V

IN

25-A

LOAD

Inhibit

–V

OUT

+V

OUT

+V

IN

–V

IN

+V

OUT

–V

OUT

VID4 – VID0

+Sns

–Sns

Share

Sync

Inhibit

–Sns

Share

Sync

Inhibit

+Sns

+V

IN

–V

IN

+V

OUT

–V

OUT

VID4 – VID0

C

IN

C

IN

D

(Required)

F1

F2

C

(Required)

+

Figure 1-1; Connection Schematic for Operation in Parallel/N+1 Configuration

flow under such conditions.

Notes

1. For ‘N+1’ redundancy, always use one more

converter than is required to supply the load.

2. The VID pins for all converter modules must be

independently set to the same voltage program code.

3. All converters connected for ‘N+1’ operation

must be located on the same printed circuit

board. A similar footprint and trace layout for

each converter will facilitate current sharing.

4 A number of high-current rectifier diodes are

available with a low forward voltage drop. They

are specifically designed for OR’ing applications

in ‘N+1’ systems. Eg. The 82CNQ030, and

MBRB2515.

5. As a result of excess capacity and the losses in the

blocking diodes, system efficiency is reduced.

6. The interconnection of pin 6 (Sync), and pin 26

(Share) between all modules are required for load

current sharing and operation at a common

frequency.