THERMAL CONSIDERATIONS
FEATURE DESCRIPTIONS (CON.)
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.
Ratio-Metric
Ratio–metric (Figure 37) is implemented by placing the
voltage divider on the TRACK pin that comprises R1 and
R2, to create a proportional voltage with VoPS1 to the
Track pin of PS2.
Hence, the choice of equipment to characterize the
thermal performance of the power module is a wind
tunnel.
For Ratio-Metric applications that need the outputs of
PS1 and PS2 reach the regulation set point at the same
time
Thermal Testing Setup
The following equation can be used to calculate the value
of R1 and R2.
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 suggested value of R2 is 10kΩ.
Vo,PS 2
R2
=
Vo,PS1 R + R2
1
PS1
PS2
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’’).
Vin
Vin
VoPS1
VoPS2
R1
TRACK
On/Off
R2
On/Off
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.
The high for positive logic
The low for negative logic
PW B
FANCING PWB
MODULE
AIR VELOCITY
AND AM BIENT
TEMPERATURE
SURED BELOW
THE MODULE
AIR FLOW
Note: Wind Tunnel Test Setup Figure Dimensions are in millimeters and (Inches)
Figure 38: Wind tunnel test setup
DS_DNL10SMD_07182012
12
DELTA [ DELTA ELECTRONICS, INC. ]
