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-

Ω 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

Ω was below 50_C.

The test ran for three hours with 2 x 50 W RMS at 1 kHz into a 6-

Ω resistive load at an ambient lab temperature

of 23

_C. No audio quality or thermal problems were encountered during that time.