DS_DNM10SIP10_03062009

11

THERMAL CONSIDERATIONS

Thermal management is an important part of the system

design. To ensure proper, reliable operation, sufficient

cooling of the power module is needed over the entire

temperature range of the module. Convection cooling is

usually the dominant mode of heat transfer.

Hence, the choice of equipment to characterize the

thermal performance of the power module is a wind

tunnel.

Thermal Testing Setup

Delta’s DC/DC power modules are characterized in

heated vertical wind tunnels that simulate the thermal

environments encountered in most electronics equipment.

This type of equipment commonly uses vertically mounted

circuit cards in cabinet racks in which the power modules

are mounted.

The

following

figure

shows

the

wind

tunnel

characterization setup. The power module is mounted on

a test PWB and is vertically positioned within the wind

tunnel. The height of this fan duct is constantly kept at

25.4mm (1’’).

Thermal Derating

Heat can be removed by increasing airflow over the

module. To enhance system reliability, the power module

should always be operated below the maximum operating

temperature. If the temperature exceeds the maximum

module temperature, reliability of the unit may be

affected.

Note: Wind Tunnel Test Setup Figure Dimensions are in millimeters and (Inches)

MODULE

AIR FLOW

12.7 (0.5”)

50.8 (2.0”)

FACING PWB

PWB

AIR VELOCITY

AND AMBIENT

TEMPERATURE

MEASURED BELOW

THE MODULE

25.4 (1.0”)

Figure 30:

Wind tunnel test setup

Ratio-Metric

Ratio–metric (Figure 29) is implemented by placing the

voltage divider on the TRACK pin that comprises R1 and

Track pin of PS2.

For Ratio-Metric applications that need the outputs of PS1

and PS2 reach the regulation set point at the same time

The following equation can be used to calculate the value

of R1 and R2.

The suggested value of R2 is 10kΩ.

,2

2

,1

1

2

oPS

oPS

V

R

VR

R

=

+

R1

R2

TRACK

PS2

PS1

Vin

Vin

On/Off

On/Off

The high for positive logic

The low for negative logic