Analog Devices EE182v01 Application Notes
Engineer-to-Engineer Note EE-182
a
Technical notes on using Analog Devices DSPs, processors and development tools
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Thermal Relief Design for ADSP-TS201S TigerSHARC® Processors
Contributed by Greg F. Rev 1 – February 3, 2004
Introduction
This EE-Note discusses thermal relief design
considerations for Analog Devices ADSPTS201S TigerSHARC® processors. This
document assists PCB and system designers by
providing thermal data as well as heat sink
recommendations to allow for proper design of
their thermal relief system.
The ADSP-TS201S processor is an ultra-highperformance, static superscalar, 32-bit processor
from the TigerSHARC family of Analog Devices
Inc. The processor core operates at a clock
frequency of 500 MHz, and is available in a flipchip ball grid array (BGA_ED) package.
Overview
This EE-Note discusses the following topics:
• Thermal overview
• Thermal calculations
• Heat sink basics
• Heat sinks: pin fins vs. rectangular-fins
• Heat sink recommendations
• Specification recommendations
• Heat sink attachment recommendations
• PCB design for thermal dissipation
• Thermal simulations
• Alternate thermal relief solutions
• Terminology
Thermal Overview
Proper thermal management is required to ensure
that the processor operates within the
temperature specifications provided in the
ADSP-TS201S data sheet [1]. Operating within
the specified temperature range ensures proper
processor operation and reliability.
The overall power estimation can also be used to
estimate a thermal relief budget for the
processor. Equation 1 gives a value for the total
average estimated power. Note that this equation
yields the total estimated average power
consumption for a single ADSP-TS201S in a
given system. Guard-banding this value is
recommended for a thermal relief design that will
allow the system to operate within specified
thermal parameters, even under worst-case
conditions.
P
Equation 1. Total Estimated Average Power
For more information on power consumption for
the ADSP-TS201, refer to the Engineer-toEngineer note EE-170, titled “Estimating Power
for ADSP-TS201S TigerSHARC Processors”
[2], which can be found on the Analog Devices
Web site, at
Figure 1 shows the top and side views of the
ADSP-TS201S processor package. This
TigerSHARC processor is available in a 25mm x
25mm BGA_ED package.
= PDD (avg.) + P
THERMAL
(avg.) + P
DD_IO
DD_DRAM
www.analog.com/tigersharc.)
(avg.)
Copyright 2004, Analog Devices, Inc. All rights reserved. Analog Devices assumes no responsibility for customer product design or the use or application of
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no responsibility is assumed by Analog Devices regarding technical accuracy and topicality of the content provided in Analog Devices’ Engineer-to-Engineer Notes.
a
that there are two possible avenues for thermal
heat dissipation: the primary heat dissipation
path (i.e., the path with the least thermal
resistance) is via the “top” of the processor
package (through the thermal path denoted by
θ
), and the secondary heat dissipation path is
JC
through the “bottom” of the processor package,
via the package balls (through the thermal path
denoted by θ
The maximal thermal energy of the processor can
be transferred when the thermal resistance from
each component in the system is minimized.
Thus, the thermal energy generated by the
processor can be dissipated to the cooler ambient
air of the system (or through the PCB by the use
of thermal vias and an internal or external heat
sinking plane).
) to the PCB.
JB
Figure 1. ADSP-TS201S Outline Diagram
The BGA_ED package consists of the laminate
(with the attached ball-grid array on its bottom
surface), and a heat spreader, which is bonded to
the processor die via a thermally conductive
adhesive. The heat spreader aids in thermal
dissipation, since it attaches directly to the
processor die and provides a much larger surface
area than the die. (Increasing the surface area
decreases the overall thermal resistance for a
given surface.)
After thermal calculations have been completed,
if it is determined that a heat sink is necessary in
the system, use a heat sink with a minimum size
of 25mm square for thermal relief of the
processor.
Figure 2 is a simple model of a thermal system,
showings the components of the processor
package. This model shows all of the associated
components present in a thermal system. Note
T
AMB
θ
JA
HEAT SPREADER
LAMINATE
PCB
Figure 2. Thermal System Model Example
THERMAL ADHESIVE
T
JUNCTION
T
CASE
θ
JC
DIE
θ
JB
Note that θJA is a composite parameter that
encompasses all possible paths to the system’s
ambient air temperature based on the JEDEC
X-Y-Z spec. (The values for θ
, θJB, and θJC are
JA
provided in the “Thermal Characteristics”
section of the ADSP-TS201S data sheet.)
Thermal Calculations
To calculate the thermal performance of a
system, the first parameter that should be known
at the time of performing thermal calculations is
the maximum ambient air temperature, T
AMBIENT
of the system. The second parameter that should
,
Thermal Relief Design for ADSP-TS201S TigerSHARC® Processors (EE-182) Page 2 of 9
a
be known is the value of the processor’s thermal
power consumption (P
THERMAL
). The third
parameter is the junction-to-ambient thermal
resistance, θ
. These three system parameters
JA
are required to calculate the maximum junction
temperature, as shown in Equation 2.
T
Equation 2. Processor Junction Temperature Calculation
JUNCTION
= (P
THERMAL
x θJA) + T
AMBIENT
From the result of Equation 2, we can then use
the calculated value for T
JUNCTION
to solve for the
calculated value for the processor's case
temperature, T
, using Equation 3. The result
CASE
of Equation 3 determines whether a heat sink is
required to allow the ADSP-TS201 to operate
within the thermal operating conditions specified
in the ADSP-TS201S data sheet. If the calculated
value for T
exceeds the maximum specified
CASE
case temperature for the device (from the ADSPTS201S data sheet), a heat sink will be required.
T
(max)= T
CASE
Equation 3. Heat Sink Requirement Equation
JUNCTION
– (P
THERMAL
x θJC)
If a heat sink is required for the processor, an
appropriate heat sink with the proper thermal
performance characteristics must be chosen. The
following two parameters for the heat sink must
be known: the sink-to-ambient (θ
) thermal
SA
resistance, and the thermal resistance of the
thermal interface material (θ
), which resides
CS
between the processor's case and the bottom
surface of the heat sink.
Knowing these two thermal resistance
parameters of the desired heat sink, we can now
calculate the case temperature (T
) of the
CASE
processor with the heat sink attached by using
Equation 4.
T
CASE (MAX)
Equation 4. Derived Heat Sink Requirement Equation
< T
AMBIENT
+ (P
THERMAL
x θSA) + (P
THERMAL
x θCS)
Equation 4 yields a conservative estimate for the
value for T
. This is because there are other
CASE
paths in the system to sink the thermal energy
(for example, through the PCB). A more
comprehensive model of the system to include
these additional paths can be used when
performing the thermal calculations for the
processor. (The value for θ
is provided in the
JB
data sheet of the ADSP-TS201S.)
Table 2 shows the thermal resistance parameters
of the BGA_ED package of the processor based
on preliminary thermal parameters.
Air Velocity
(m/s)
0 19.6 8.3 0.7
1 15.4 8.3 0.7
2 13.7 8.3 0.7
Table 2. BGA_ED Thermal Resistance Parameters
θ
Without
JA
Heat Sink (°C/W)
θ
Nominal
JB
(°C/W)
θ
Nominal
JC
(°C/W)
Table 3 shows thermal resistance values for an
AAVID 374224B00032 heat sink. The values
shown in Table 3 are provided as an example.
Air Velocity
(m/s)
0 19.7 10.7
1 6.4 5.5
2 4.8 4.5
Table 3. Heat Sink Thermal Resistance Example
θ
Heat Sink
SA
Resistance (°C/W)
θ
With Heat Sink
JA
(°C/W)
For a specific application, the heat sink’s thermal
resistance values can be obtained from the
particular heat sink vendor.
Using Equation 4 and the data from Table 3, the
required minimal airflow over the heat sink can
be determined to allow for operating the
ADSP-TS201S within the maximum case
temperature specified in the processor's data
sheet. If this value is still insufficient, an active
thermal relief solution is required. See “Alternate
Thermal Relief Designs” later in this document.
If the resultant value from Equation 4 exceeds
the maximum value for T
CASE (MAX)
(from the
ADSP-TS201S data sheet), a heat sink with
better thermal characteristics will be required.
Thermal Relief Design for ADSP-TS201S TigerSHARC® Processors (EE-182) Page 3 of 9
Heat Sink Basics
A heat sink is characterized by its thermal
resistance, which describes the flow of heat from
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