Voltage Transformation Module

VT048A040T050FP

vicorpower.com

Rev. 1.0

Page 7 of 11

APPLICATION NOTES & TEST CIRCUIT

Parallel Operation

In applications requiring higher current or redundancy, VTMs can be

operated in parallel without adding control circuitry or signal lines. To

maximize current sharing accuracy, it is imperative that the source and

load impedance on each VTM in a parallel array be equal. If VTMs are

being fed by an upstream PRM, the VC nodes of all VTMs must be con-

nected to the PRM VC.

To achieve matched impedances, dedicated power planes within the PC

board should be used for the output and output return paths to the

array of paralleled VTMs. This technique is preferable to using traces of

varying size and length.

The VTM power train and control architecture allow bi-directional power

transfer when the VTM is operating within its specified ranges. Bi-direc-

tional power processing improves transient response in the event of an

output load dump. The VTM may operate in reverse, returning output

power back to the input source. It does so efficiently.

Input Impedance Recommendations

To take full advantage of the VTM’s capabilities, the impedance of the

source (input source plus the PC board impedance) must be low over a

range from DC to 5 MHz. The input of the VTM (factorized bus) should

be locally bypassed with a 8 µF low Q aluminum electrolytic capacitor.

Additional input capacitance may be added to improve transient

performance or compensate for high source impedance. The VTM has

extremely wide bandwidth so the source response to transients is usually

the limiting factor in overall output response of the VTM.

Anomalies in the response of the source will appear at the output of the

VTM, multiplied by its K factor of 1/12. The DC resistance of the source

should be kept as low as possible to minimize voltage deviations on the

input to the VTM. If the VTM is going to be operating close to the high

limit of its input range, make sure input voltage deviations will not trig-

ger the input overvoltage turn-off threshold.

Input Fuse Recommendations

VI BRICKs are not internally fused in order to provide flexibility in config-

uring power systems. However, input line fusing of VI BRICKs must

always be incorporated within the power system. A fast acting fuse is

required to meet safety agency Conditions of Acceptability. The input

line fuse should be placed in series with the +In port. For agency

approvals and fusing conditions, click on the link below:

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

and_certification/safety_approvals/

Application Notes

For VTM 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.

F1

Load

+

–

Input reflected ripple

measurement point

C2

0.47

μF

ceramic

+

–

14 V

VTM

+IN

+OUT

-OUT

+OUT

-OUT

-IN

TM

VC

PC

Figure 10 — VI BRICK VTM test circuit

Notes:

1. C3 should be placed close to the load

2. R3 may be ESR of C3 or a separate damping resistor.

C3

47 µF

R3

10 m

Ω

C1

47 µF

Al electrolytic

Fuse