Datasheet

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REFERENCES
TAS5121I
SLES122 – SEPTEMBER 2004
APPLICATION INFORMATION (continued)
36-pin PSOP3 0.47 ° C/W
The thermal resistance of thermally conductive pads is generally higher than a thin thermal grease layer.
Thermal tape has an even higher thermal resistance and should not be used with this package.
Heatsink thermal resistance is generally predicted by the heatsink vendor, modeled using a continuous flow
dynamics (CFD) model, or measured.
Thus, for a single monaural IC, the system R
θ JA
= R
θ JC
+ thermal grease resistance + heatsink resistance.
Table 7 indicates modeled parameters for one TAS5121I IC on a heatsink. The junction temperature is set at
110 ° C while delivering 70 W RMS into 4- Ω loads with no clipping. It is assumed that the thermal grease is about
0.001 inch thick (this is critical).
Table 7. Example of Thermal Simulation
36-PIN PSOP3
Ambient temperature 25 ° C
Power to load 70 W
Delta T inside package 5.5 ° C
Delta T through thermal grease 3.2 ° C
Required heatsink thermal resistance 11.0 ° C/W
Junction temperature 110 ° C
System R
θ JA
12.3 ° C/W
R
θ JA
* power dissipation 85 ° C
R
θ JC
0.85 ° C/W
As an indication of the importance of keeping the thermal grease layer thin, if the thermal grease layer increases
to 0.002 inches thick, the required heatsink thermal resistance increases to 5.2 ° C/W for the PSOP3 package.
1. Digital Audio Measurements application report – TI (SLAA114 )
2. PowerPAD™ Thermally Enhanced Package technical brief – TI (SLMA002 )
3. System Design Considerations for True Digital Audio Power Amplifiers application report – TI (SLAA117 )
4. Voltage Spike Measurement Technique and Specification application note – TI (SLEA025 )
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