Datasheet

TAS5414A, TAS5424A
www.ti.com SLOS535C –MAY 2009– REVISED APRIL 2011
• Thermal grease thermal resistance
• Heat sink thermal resistance
The thermal grease thermal resistance can be calculated from the exposed heat slug area and the thermal
grease manufacturer's area thermal resistance (expressed in °C-in
2
/W or °C-mm
2
/W). The area thermal
resistance of the example thermal grease with a 0.001-inch (0.0254-mm) thick layer is about 0.007°C-in
2
/W
(4.52°C-mm
2
/W). The approximate exposed heat slug size is as follows:
TAS5424A, 44-pin PSOP3 …………………. 0.124 in
2
(80 mm
2
)
TAS5414A, 36-pin PSOP3 …………………. 0.124 in
2
(80 mm
2
)
TAS5414A, TAS5424A, 64-pin QFP……….. 0.099 in
2
(64 mm
2
)
Dividing the example thermal grease area resistance by the area of the heat slug gives the actual resistance
through the thermal grease for both parts:
TAS5424A, 44-pin PSOP3 …………………. 0.06°C/W
TAS5414A, 36-pin PSOP3 …………………. 0.06°C/W
TAS5414A, TAS5424A, 64-pin QFP……….. 0.07°C/W
The thermal resistance of thermal pads is generally considerably higher than a thin thermal grease layer.
Thermal tape has an even higher thermal resistance and should not be used at all. Heat sink thermal resistance
generally is predicted by the heat sink vendor, modeled using a continuous flow dynamics (CFD) model, or
measured.
Thus, for a single monaural channel in the IC, the system R
θJA
= R
θJC
+ thermal grease resistance + heat sink
resistance.
The following table indicates modeled parameters for one TAS5414A or TAS5424A IC on a heat sink. The
junction temperature is set at 115°C in both cases while delivering 20 Wrms per channel into 4-Ω loads with no
clipping. It is assumed that the thermal grease is about 0.001 inches (0.0254 mm) thick.
Device TAS5414A, 36-Pin PSOP3
Ambient temperature 25°C
Power to load 20 W × 4
Power dissipation 1.90 W × 4
ΔT inside package 7.6°C
ΔT through thermal grease 0.46°C
Required heatsink thermal resistance 10.78°C/W
Junction temperature 115°C
System R
θJA
11.85°C/W
R
θJA
× power dissipation 90°C
Electrical Connection of Heat Slug and Heat Sink
Any heat sink that is connected to the heat slug of the TAS5414A or TAS5424A should be connected to GND or
left floating. The heat slug should never be connected to any electrical node other than GND.
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