
TAS5110
SLES028A
–
MAY 2002
–
REVISED SEPTEMBER 2002
16
www.ti.com
Aluminum Chassis 7.2 in x 1 in x 0.1 in Thick Sides of U-Shaped
Chassis Are 1.25 in High (3.9
°
C/W)
Wakefield Type 126
Thermal Compound
(0.169
°
C/W)
1.25 in
Aluminum Space Bar (1/4 in Thick)
(0.558
°
C/W)
32 DAD Packages
(1.6
°
C/W)
2.33 in
Stereo Amplifier Board
4-40 Machine Screws With
Star Washers
Plastic Top and Insulating
Front and Back Panels
1 mm
Wakefield Type 126
Thermal Compound
(3.2
°
C/W)
Figure 8. 32-Pin DAD Package Cross-Sectional View (Front)
Thermal Methodology for the 32-Pin DAP Package 50 W, 6-
Test
The thermal test for the DAP part (e.g., thermal pad soldered to the board) was conducted as shown in Figure 9
and Figure 10. The cooling approach was to conduct the dissipated heat into the via pad on the board, through
the vias in the board, and into a heat sink.
The lower via pad area, slightly larger than the IC pad itself, was exposed with a window in the solder resist on
the bottom surface of the board. It was not coated with solder during the board construction to maintain a flat
surface. In production, this could be accomplished with a peelable solder mask.
A spacer bar was used to keep the through-hole leads from shorting to the chassis. The thermal compound
indicated yielded a pad-to-spacer thermal resistance of about 3.2 C/W.
The chassis provided the only heat sink to air and was chosen as representative of a possible cooling approach.
A plastic top and insulating front and back panels were used to ensure that only the bottom and sides of the U
shaped chassis contributed to cooling. The chassis was spaced 0.25 inch from the table to simulate a normal
chassis configuration. (Any heat sink with a thermal resistance to air of 3.9 C/W or lower also works.) In this
test, the exposed chassis reached long-term equilibrium temperatures above 50 C, so the approach would
have to be modified for touch temperature consideration. The chassis temperature after 10 minutes of 50 W
into 6
was below 50 C.
The test ran for three hours with 2 x 50 W RMS at 1 kHz into a 6-
resistive load at an ambient lab temperature
of 23 C. No audio quality or thermal problems were encountered during that time.