Pre-Regulator Module

PR024A480T012FP

vicorpower.com

Rev. 1.1

Page 11 of 13

APPLICATION NOTES

OVP – Overvoltage Protection

The output Overvoltage Protection set point of the PR024A480T012FP is

factory preset for 56 V. If this threshold is exceeded the output shuts down

and a restart sequence is initiated, also indicated by PC pulsing. If the

condition that causes OVP is still present, the unit will again shut down.

This cycle will be repeated until the fault condition is removed. The OVP set

point may be set at the factory to meet unique high voltage requirements.

PRM Output Power Versus VTM Output Power

As shown in Figure 17, the PR024A480T012FP is rated to deliver 2.5 A

maximum, when it is delivering an output voltage in the range from 26 V

to 48 V, and 120 W, maximum, when delivering an output voltage in the

range from 48 V to 55 V. When configuring a PRM for use with a specific

VTM, refer to the appropriate VTM data sheet. The VTM input power can

be calculated by dividing the VTM output power by the VTM efficiency

(available from the VTM data sheet). The input power required by the VTM

should not exceed the output power rating of the PRM.

The Factorized Bus voltage should not exceed an absolute limit of 55 V,

including steady state, ripple and transient conditions. Exceeding this limit

may cause the internal OVP set point to be exceeded.

Parallel Considerations

The PR port is used to connect two PRMs in parallel to form a higher

power array. When configuring arrays, PR port interconnection terminating

impedance is 10 k to SG. See note Page 8 and refer to Application Note

AN002. Additionally one PRM should be designated as the master while all

other PRMs are set as slaves by shorting their SC pin to SG. The PC pins

must be directly connected (no diodes) to assure a uniform start up

sequence. Consult Vicor applications engineering for applications requiring

more than two PRMs.

Adjusting Current Limit

The current limit can be lowered by placing an external resistor between

open-circuit, the current limit is preset to be within the range specified in

the output specifications table on Page 4.

Input Fuse Recommendations

A fuse should be incorporated at the input to the PRM, in series with the

+In port. A fast acting fuse, NANO2 FUSE 451/453 Series 10 A 125 V, or

equivalent, may be required to meet certain safety agency Conditions of

Acceptability. Always ascertain and observe the safety, regulatory, or other

agency specifications that apply to your specific application. For agency

approvals and fusing conditions, click on the link below:

http://www.vicorpower.com/technical_library/technical_documentation/quality_and_

certification/safety_approvals/

Product Safety Considerations

If the input of the PRM is connected to SELV or ELV circuits, the output of

the PRM can be considered SELV or ELV respectively.

If the input of the PRM is connected to a centralized DC power system

where the working or float voltage is above SELV, but less than or equal to

75 V, the input and output voltage of the PRM should be classified as a

TNV-2 circuit and spaced 1.3 mm from SELV circuitry or accessible

conductive parts according to the requirements of UL60950-1,

CSA 22.2 60950-1, EN60950-1, and IEC60950-1.

Application Notes

For PRM and VI BRICK application notes on soldering, board layout, and

system design please click on the link below:

http://www.vicorpower.com/technical_library/application_information/

Applications Assistance

Please contact Vicor Applications Engineering for assistance,

1-800-927-9474, or email at apps@vicorpower.com.

1.00

10.00

100.00

0.5

1

1.5

2

2.5

Desired PRM Output Current Limit (A)

Figure 18 — Calculated external resistor value for adjusting current limit, actual

value may vary.

26

30

34

38

42

46

50

54

2.30

2.35

2.40

2.45

2.50

2.55

28

32

36

40

44

48

52

2.25

2.20

2.15

60

20

~

~

0

22 24

56 58

Safe Operating Area

Figure 17 — PR024A480T012FP rating based on Factorized Bus voltage