VISHAY MHSL10055

Technical Note
July 1996
Thermal Management for FC- and FW-Series
250 W—300 W Board-Mounted Power Modules
Introduction
Basic Thermal Management
Board-mounted power modules (BMPMs) enhance
the capabilities of advanced computer and communications systems by providing flexible power architectures; however, proper cooling of the power modules
is required for reliable and consistent operation.
Maintaining the operating case temperature (Tc)
within the specified range keeps internal component
temperatures within their specifications. This, in turn,
helps keep the expected mean time between failures
(MTBF) from falling below the specified rating.
Proper cooling can be verified by measuring the case
temperature of the module (Tc) at the location indicated in Figure 1. Note that the view in Figure 1 is of
the metal surface of the module (the pin locations
shown are for reference). Tc must not exceed 100 °C
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 as close as possible to
the indicated position, taking into account the contact
resistance between the mounting surface and the
heat sink (see Heat Sink section).
Tyco's FC- and FW- Series 250 W to 300 W BMPMs
are designed with high efficiency as a primary goal.
The 5 V output units have typical full load efficiencies
of 83%, which result in less heat dissipation and
lower operating temperatures. Also, these modules
use temperature resistant components, such as
ceramic capacitors, that do not exhibit wearout
behavior during prolonged exposure to high temperatures, as do aluminum electrolytic capacitors.
VI(+)
MEASURE CASE
TEMPERATURE HERE
VO(+)
VI(–)
ON/OFF
SYNC IN
This application note provides the necessary information to verify that adequate cooling is present in a
given operating environment. This information is
applicable to all Tyco 250 W to 300 W BMPMs in the
4.6 in. x 2.4 in. x 0.5 in. package.
1.20 (30.5)
VO(–)
SYNC OUT
CASE
3.25 (82.6)
8-1303a
Figure 1. Case Temperature Measurement (Metal
Side)
While this is a valid method of checking for proper
thermal management, it it is only usable if the final
system configuration exists and can be used as a
test environment. The graphs on the accompanying
pages provide guidelines to predict the thermal performance of the module for typical configurations that
include heat sinks in natural or forced airflow environments. However, due to differences between the test
setup and the final system environment, the module
case temperature must always be checked in the
final system configuration to verify proper operation.
Thermal Management for FC- and FW-Series
250 W—300 W Board-Mounted Power Modules
Technical Note
July 1996
Basic Thermal Management (continued)
Module Derating
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 the output power (Po) as shown by the equation below:
Experimental Setup
PD = PI – Po
Also, module efficiency (η) is defined as the ratio of
output power to input power as shown by the equation
below:
The derating curves in the following figures were
obtained from measurements obtained in an experimental apparatus shown in Figure 3. Note that the
module and the printed-wiring board (PWB) onto which
it was mounted were vertically oriented. The passage
has a rectangular cross-section. The clearance
between the top of the module and the facing PWB was
kept constant at 0.5 in.
η = Po / PI
The input power term can be eliminated by the combination of these two equations to yield the equation
below:
PD = Po (1 – η) / η
PWB
FACING
PWB
This equation can be used to calculate the module
power dissipation. However, efficiency is a nonlinear
function of the module input voltage (VI) and output
current (Io). Typically, a plot of power dissipation versus
output current over three different line voltages is given
in each module-specific data sheet. This is because
each module has a different power dissipation curve. A
typical curve of this type is shown below in Figure 2 for
a FW300A1 Power Module (5 V output voltage).
AIR VELOCITY
AND AMBIENT
TEMPERATURE
MEASURED
HERE
POWER DISSIPATION, PD (W)
70
60
50
V = 72 V
V = 54 V
V = 36 V
40
30
AIRFLOW
20
8-690a
10
Figure 3. Experimental Test Setup
0
0
10
20
30
40
50
60
OUTPUT CURRENT, IO (A)
8-1313
Figure 2. FW300A1 Power Dissipation vs. Output
Current
2
Tyco Electronics Corp.
Thermal Management for FC- and FW-Series
250 W—300 W Board-Mounted Power Modules
Technical Note
July 1996
Module Derating (continued)
Convection Without Heat Sinks
Increasing airflow over the module enhances heat
transfer via convection. Figures 4 and 5 show the maximum power that can be dissipated by the module without exceeding the maximum case temperature versus
local ambient temperature (TA) for natural convection
through 800 ft./min. A natural convection condition is
produced when air is moved only through the buoyancy
effects produced by a temperature gradient between
the module and surrounding air. In the test setup used,
natural convection airflow was measured at 10 ft./min.
to 20 ft./min., whereas systems in which these power
modules may be used typically generate natural convection airflow rates of 60 ft./min. due to other heat dissipating components in the system. The 100 ft./min. to
800 ft./min. curves are for airflow added externally to
the test setup, usually through the use of fans. Note
that there is a thermal performance improvement when
the long axis of the module is perpendicular to the airflow direction (transverse orientation).
POWER DISSIPATION, PD (W)
70
800 ft./min.
700 ft./min.
600 ft./min.
500 ft./min.
400 ft./min.
300 ft./min.
200 ft./min.
100 ft./min.
60
50
40
30
POWER DISSIPATION, PD (W)
70
800 ft./min.
700 ft./min.
600 ft./min.
500 ft./min.
400 ft./min.
300 ft./min.
200 ft./min.
100 ft./min.
60
50
40
30
20
10
20 ft./min. (NAT. CONV.)
0
0
10
20
30
40
50
60
70
80
90 100
LOCAL AMBIENT TEMPERATURE, TA (°C)
8-1315
Figure 5. Convection Power Derating with No
Heat Sink; Airflow Along Width (Transverse)
Figures 4 and 5 can be used to determine the appropriate airflow for a given set of operating conditions as
shown in the following examples.
Example 1: Airflow Required to Maintain Tc
What is the minimum airflow necessary for a FW300A1
in the transverse orientation, operating at 54 V input, an
output current of 50 A, and a maximum ambient temperature of 35 °C?
Solution:
Given: VI = 54 V, Io = 50 A, TA = 35 °C
Determine PD (Figure 2): PD = 46 W
Determine Airflow (Figure 5): v = 800 ft./min.
20
10
20 ft./min. (NAT. CONV.)
0
0
10
20
30
40
50
60
70
80
90 100
Example 2: Maximum Power Output
LOCAL AMBIENT TEMPERATURE, TA (°C)
8-1314
Figure 4. Convection Power Derating with No
Heat Sink; Airflow Along Length (Longitudinal)
What is the maximum power output for a FW300A1 in
the longitudinal orientation, operating at 54 V input, in
an environment that provides 600 ft./min. with a maximum ambient temperature of 40 °C?
Solution:
Given: VI = 54 V, v = 600 ft./min., TA = 40 °C
Determine PD (Figure 4): PD = 34 W
Determine Io (Figure 2): Io = 40 A
Calculate Po = (Vo) * (Io) = 5 x 40 = 200 W
Although the above two examples use 100 °C as the
operating case temperature, for extremely high reliability applications, one may design to a lower case temperature as shown later in Example 4.
Tyco Electronics Corp.
3
Thermal Management for FC- and FW-Series
250 W—300 W Board-Mounted Power Modules
Technical Note
July 1996
Module Derating (continued)
Heat Sink Configuration
Several standard heat sinks are available for the FC- and FW-Series 250 W—300 W BMPMs, as shown in Figures
6 and 7. The heat sinks mount to the top surface of the module with M3 x 0.5 screws torqued to 5 in.-lb. (0.56 N-m).
Placing a thermally conductive dry pad or thermal grease between the case and the heat sink minimizes contact
resistance (typically 0.1 °C/W to 0.3 °C/W) and temperature drop. All heat sink curve data taken had such a dry
pad present.
1/4 IN. (MHSL02555)
1/2 IN. (MHSL05055)
1 IN. (MHSL10055)
4.56
1 1/2 IN. (MHSL15055)
2.36
8-1316
Figure 6. Heat Sinks with Longitudinal Fins
4
Tyco Electronics Corp.
Thermal Management for FC- and FW-Series
250 W—300 W Board-Mounted Power Modules
Technical Note
July 1996
Module Derating (continued)
Heat Sink Configuration (continued)
1/4 IN. (MHST02555)
2.36
1/2 IN. (MHST05065)
1 IN. (MHST10055)
4.56
1 1/2 IN. (MHST15055)
8-1317
Figure 7. Heat Sinks with Transverse Fins
Nomenclature for this family of heat sinks is as follows:
MHSxyyy55
where:
x = fin orientation; longitudinal (L) or transverse (T)
yyy = heat sink height (in 100ths of inch)
For example, MHST10055 is a heat sink that is transverse mounted (see Figure 7) for a 4.6 in. x 2.4 in. module
with a heat sink height of 1 in. The “M” prefix represents a heat sink kit with metric hardware.
Tyco Electronics Corp.
5
Thermal Management for FC- and FW-Series
250 W—300 W Board-Mounted Power Modules
Technical Note
July 1996
Module Derating (continued)
Natural Convection With Heat Sinks
Figures 8 and 9 show the power derating for a module
in natural convection with the heat sinks shown in Figures 6 and 7. Natural convection is the heat transfer
produced when air in contact with a hot surface is
heated, causing it to rise. An open environment is
required with no external forces moving the air. Figures
8 and 9 apply when the module is the only source of
heat present in the system, generating airflow of
approximately 10 ft./min. to 20 ft./min. Again, a typical
system with other heat dissipating components will
usually generate higher airflows in natural convection.
POWER DISSIPATION, PD (W)
70
60
1 1/2 in.
1 in.
1/2 in.
1/4 in.
NONE
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90 100
LOCAL AMBIENT TEMPERATURE, TA (°C)
8-1319
POWER DISSIPATION, PD (W)
70
Figure 9. Heat Sink Power Derating Curves
Natural Convection, Transverse Orientation
60
1 1/2 in.
1 in.
1/2 in.
1/4 in.
NONE
50
40
Figures 8 and 9 can be used to predict which heat sink
a module will require in a natural convection environment, as shown in the following example.
30
20
Example 3: Sizing a Heat Sink
10
0
0
10
20
30
40
50
60
70
80
90 100
LOCAL AMBIENT TEMPERATURE, TA (°C)
What heat sink would be appropriate for a transverse
mounted FW300A1 in a natural convection environment at 54 V input and 2/3 load with a maximum ambient temperature of 35 °C?
8-1318
Figure 8. Heat Sink Power Derating Curves
Natural Convection, Longitudinal Orientation
6
Solution:
Given: VI = 54 V, Io = 2/3(60) = 40 A, TA = 35 °C
Determine PD (Figure 2): PD = 35 W
Determine Heat Sink (Figure 9):
1 1/2 in. heat sink allows up to TA = 35 °C
Tyco Electronics Corp.
Thermal Management for FC- and FW-Series
250 W—300 W Board-Mounted Power Modules
Technical Note
July 1996
Basic Thermal Model
θ = ∆Tc,max / PD
This can be represented as an equivalent circuit as
shown in Figure 10. In this model PD, ∆Tc,max, and θ
are analogous to current flow, voltage drop, and electrical resistance, respectively, in Ohm's law. Also,
∆Tc,max is defined as the difference between the inlet
ambient temperature (TA) and the module case temperature (Tc) as defined in Figures 3 and 1 respectively.
CASE-TO-AMBIENT THERMAL
RESISTANCE, RCA (°C/W)
4.5
Another approach for analyzing thermal performance is
to model the overall thermal resistance of the module.
This presentation method is especially useful when
considering heat sinks, since their performance is also
typically given as a resistance. Total module thermal
resistance (θ) is defined as the maximum case temperature rise (∆Tc,max) divided by the module power dissipation (PD):
1 1/2 in. HEAT SINK
1 in. HEAT SINK
1/2 in. HEAT SINK
1/4 in. HEAT SINK
NO HEAT SINK
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
100
200
300
400
500
600
AIR VELOCITY, (ft./min.)
8-1320
Figure 11. Case-to-Ambient Thermal Resistance
Curves, Longitudinal Orientation
∆Tc,max = Tc – TA
BMPM
PD
= BMPM
THERMAL
RESISTANCE
8-695
Figure 10. Basic Thermal Resistance Module
For FC- and FW-Series 250 W to 300 W BMPMs, the
module's thermal resistance values versus air velocity
have been determined experimentally and are plotted
in Figures 11 and 12 for a unit without a heat sink and
for the various heat sink configurations (see Figures 6
and 7). Note that the highest values on the curves represent natural convection. In a system with free-flowing
air and other heat sources, there may be additional airflow.
CASE-TO-AMBIENT THERMAL
RESISTANCE, RCA (°C/W)
4.5
1 1/2 in. HEAT SINK
1 in. HEAT SINK
1/2 in. HEAT SINK
1/4 in. HEAT SINK
NO HEAT SINK
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
100
200
300
400
500
600
AIR VELOCITY, (ft./min.)
8-1321
Figure 12. Case-to-Ambient Thermal Resistance
Curves; Transverse Orientation
It is important to point out that the thermal resistances
shown in Figures 11 and 12 are for heat transfer from
the sides and bottom of the module as well as the top
side with the attached heat sink; therefore, the case-toambient thermal resistances shown will generally be
lower than the resistance of the heat sink by itself. The
data in Figures 11 and 12 were taken with a thermally
conductive dry pad between the case and the heat sink
to minimize contact resistance (typically 0.1 °C/W to
0.3 °C/W).
Tyco Electronics Corp.
7
Thermal Management for FC- and FW-Series
250 W—300 W Board-Mounted Power Modules
Technical Note
July 1996
Basic Thermal Model (continued)
Example 5: Determining Tc
Figures 11 and 12 can be used to determine thermal
performance under various airflow and heat sink configurations as shown in the following examples.
Suppose that there is an air velocity of 600 ft./min.
available for the configuration stated in Example 4.
What is the case temperature for the various heat sink
configurations?
Example 4: Airflow Required to Maintain Tc
Although the maximum case temperature for the FCand FW-Series 250 W—300 W BMPMs is 100 °C, one
may want to limit the maximum case temperature to a
lower value for extremely high reliability. If an 85 °C
case temperature is desired, what are the allowable
minimum airflow/heat sink combinations necessary for
a transverse mounted FW300A1 operating at 54 V
input line and an output current of 50 A with a maximum ambient of 40 °C?
Solution:
Given: VI = 54 V, Io = 50 A, TA = 40 °C
Determine PD (Figure 2): PD = 46 W
θ = (Tc – TA) / PD
= (85 – 40) / 46
= 1.0 °C/W
Use Figure 12 to determine air velocity:
No heat sink:
v >> 600 ft./min.
1/4 in. heat sink:
v >> 600 ft./min.
1/2 in. heat sink:
v = 450 ft./min.
1 in. heat sink:
v = 260 ft./min.
1 1/2 in. heat sink:
v = 205 ft./min.
Solution:
Given: VI = 54 V, Io = 50 A, TA = 40 °C, v = 600 ft./min.
Determine PD (Figure 2): PD = 46 W
Tc = (θ x PD) + TA
Using thermal resistances (θ) from Figure 12:
No heat sink: θ = 1.5 °C/W
Tc = (1.5 x 46) + 40 = 109 °C
1/4 in. heat sink: θ = 1.2 °C/W
Tc = (1.2 x 46) + 40 = 95 °C
1/2 in. heat sink: θ = 0.9 °C/W
Tc = (0.9 x 46) + 40 = 81 °C
1 in. heat sink: θ = 0.6 °C/W
Tc = (0.6 x 46) + 40 = 68 °C
1 1/2 in. heat sink: θ = 0.5 °C/W
Tc = (0.5 x 46) + 40 = 63 °C
In this configuration, the module would not operate
within the maximum case temperature of 100 °C unless
a heat sink was attached.
Thermal Shutdown
The FC- and FW-Series 250 W—300 W BMPMs has a
latching thermal shutdown circuit designed to turn off
the module if it is operated in excess of the maximum
case temperature. Recovery from thermal shutdown is
accomplished by cycling the dc input power off for at
least 1.0 s, or toggling the primary referenced ON/OFF
signal for at least 1.0 s.
Tyco Electronics Power Systems, Inc.
3000 Skyline Drive, Mesquite, TX 75149, USA
+1-800-526-7819 FAX: +1-888-315-5182
(Outside U.S.A.: +1-972-284-2626, FAX: +1-972-284-2900)
http://power.tycoelectronics.com
Tyco Electronics Corporation reserves the right to make changes to the product(s) or information contained herein without notice. No liability is assumed as a result of their use or application.
No rights under any patent accompany the sale of any such product(s) or information.
© 2001 Tyco Electronics Corporation, Harrisburg, PA. All International Rights Reserved.
Printed in U.S.A.
July 1996
TN96-009EPS
Printed on
Recycled Paper