FE150H Datasheet, PDF (1/8 Pages) Tyco Electronics – Thermal Management for High-Power Board-Mounted Power Modules

Technical Note
August 1997
Thermal Management for
High-Power Board-Mounted Power Modules
Introduction
Board-mounted power modules (BMPMs) enhance
the capabilities of advanced computer and communi-
cations systems by providing flexible power architec-
tures; however, proper cooling of the power modules is
required for reliable and consistent operation. Main-
taining the operating case temperature (TC) within the
specified range keeps internal-component tempera-
tures within their specifications, which, in turn, helps
keep the expected mean time between failures
(MTBF) from falling below the specified rating.
Tyco's FC-, FE-, and FW-Series 50 W to 200 W
BMPMs are designed with high efficiency as a pri-
mary goal. The 5 V output units have typical full-load
efficiencies greater than 80%, which result in less
heat dissipation and lower module case tempera-
tures. Furthermore, these modules use temperature-
resistant components, such as ceramic capacitors,
that do not degrade during prolonged exposure to
high temperatures, as do aluminum electrolytic
capacitors.
This application note provides the information to ver-
ify that adequate cooling is present in a given operat-
ing environment. A thermal model is included that
can be used to design heat sinks and other means
for meeting the cooling and reliability requirements
for a given application. The information can be
applied to all Tyco high-power BMPMs in the
121.9 mm x 63.5 mm x 12.7 mm (4.8 in. x 2.5 in. x
0.5 in.) package.
Basic Thermal Management
Proper cooling can be verified by measuring the TC of
the module at the location indicated in Figure 1. TC
must not exceed 95 °C (85 °C for 200 W modules)
while operating in the final system configuration.
After the module has reached thermal equilibrium,
the measurement can be made with a thermocouple
or surface probe. If a heat sink is mounted to the
case, make the measurement on the base of the heat
sink as close as possible to the indicated position,
taking into account the contact resistance between
the mounting surface and the heat sink (see Detailed
Thermal Model section).
76 (3.0)
MEASURE CASE
TEMPERATURE HERE
18 (0.7)
Lucent
CASE
ON/OFF
+
IN
–
FE150A
DC-DC Power Module
IN:DC 48V, 3.7A OUT:DC 5V, 30A
150W
MADE IN USA
6238
TUV Rheinland
Protected by U.S. Patents: 5,036,452 5,179,365
PARALLEL
+
SENSE
–
–
OUT
+
Note: Top view, pin locations are for reference.
Dimensions shown in millimeters and (inches).
8-582(C).c
Figure 1. Case Temperature Measurement
While this is a valid method to check for proper ther-
mal management, it makes the assumption that the
final system configuration exists and can be used for
a test environment or can be modeled. The following
graphs provide guidelines to predict the thermal
performance of the module for typical configurations
that include heat sinks in natural or forced-airflow
environments.
The goal of thermal management is to transfer the
heat dissipated by the module to the surrounding
environment. The amount of power dissipated by the
module as heat (PD) is the difference between the
input power (PI) and output power (PO) as shown by
the equation below:
PD = PI – PO
Also, module efficiency (η) is defined as the ratio of
output power to input power, shown by the following
equation:
η
=
PO
--_P----_I-
The input power term can be eliminated by combin-
ing these two equations. They yield the equation
below, which can be used to calculate module power
dissipation:
PD
=
PO(1 – η)
------------_η-------------