UHP28_2_12A Datasheet, PDF (9/9 Pages) Murata Manufacturing Co., Ltd. – Isolated, 12 Amp Half Brick, 48VIN/28.2VOUT DC/DC Converters

Thermal Management
“Zero Airflow” Passive Cooling Enclosure Installations
The UHP-28.2/12-D48 converter will deliver its full rated power as long as
the user maintains the baseplate at +80°C or less. Usable power is available
derated up to +110°C baseplate temperature. Please see the “baseplate”
Derating curve below. This curve is different from standard Derating curves
because no airflow is indicated. This is a reflection of the requirement to
only limit the baseplate temperature since the majority of the heat flows out
through the baseplate. Some heat is removed via airflow convection over the
converter.
UHP-28.2/12-D48N Maximum Baseplate Temperature vs. Output Power (6).6








                  
Baseplate Temperature (_°C)
Figure 9. Maximum Baseplate Temperature vs. Output Power
UHP-28.2/12-D48
Isolated, 12 Amp Half Brick, 48VIN/28.2VOUT DC/DC Converters
“No airflow” applications are normally those with the converter bolted to a
chassis wall or other large heat-conducting surface. For such wall installa-
tions, there is no explicit airflow specification and the converter may be used
with zero airflow as long as the baseplate does not exceed +110°C.
Consider using thermal pads or compound (“thermal grease”) to lower the
thermal resistance between the baseplate and the chassis wall. Do not rely
only on the baseplate mounting screws to transfer heat. Also, since a housing
wall is not an infinite heat sink, most real-world enclosure installations are
improved by moderate forced airflow. This airflow cools both the mounting
surface and the converter itself by convection. Larger area and/or a thicker
mounting surface material will conduct more heat away and allow higher
output power.
Because of the high efficiency of the converter, the mounting surface only
carries away the internal dissipation of the converter, not the entire power
output. For computation purposes, the enclosure surface may use the follow-
ing dissipation equations:
P(diss) = PowerIn – PowerOut and,
PowerOut / PowerIn x 100 = Efficiency (in %) and,
P(diss) = PowerIn (1 – Efficiency/100)
where “P(diss)” is the internal power dissipation of the converter.
Efficiency is given in percent. For example, with 92% efficiency at VIN = 48V
and 300 Watts out, P(diss) is 24 Watts.
Heat Sink Usage
The UHP-28.2/12-D48 converter is primarily intended for baseplate and
enclosure mount installations. However, if you prefer to attach the converter’s
baseplate to an extruded aluminum heatsink in a traditional fan-forced airflow
installation, the user must carefully compute the thermal resistance of the
heat sink versus the power dissipation versus the ambient temperature and
airflow over the heatsink. As with the passive mounting surface installations,
the baseplate temperature should never exceed +110°C.
Murata Power Solutions, Inc.
11 Cabot Boulevard, Mansfield, MA 02048-1151 U.S.A.
Tel: [phone] [phone] Fax: [phone]
www.murata-ps.com email: [e-mail] ISO 9001 REGISTERED
07/10/08
Murata Power Solutions, Inc. makes no representation that the use of its products in the circuits described herein, or the use of other
technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein do not imply
the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifications are subject to change without
notice.
© 2008 Murata Power Solutions, Inc.
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UHP_28.2/12_D48.B02 Page 9 of 9