Datasheet

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I − Current − A
4
5
6
7
8
9
10
11
0 5 10 15
L − Inductance − µH
INDUCTANCE
vs
CURRENT
DBF1310A
DASL983XX−1023
THERMAL INFORMATION
TAS5121I
SLES122 – SEPTEMBER 2004
APPLICATION INFORMATION (continued)
Figure 10. Inductance Saturation
The selection of the capacitors that are placed from the output of each inductor to ground is simple. To complete
the output filter, use a 1- µ F capacitor with a voltage rating at least twice the voltage applied to the output stage
(PVDD_x).
This capacitor should be a good quality polyester dielectric.
The following information is provided as an example.
The thermally enhanced package provided with the TAS5121I is designed to be interfaced directly to a heatsink
using a thermal interface compound (for example, Wakefield Engineering type 126 thermal grease.) The heatsink
then absorbs heat from the ICs and transfers it to the ambient air. If the heatsink is carefully designed, this
process can reach equilibrium and heat can be continually removed from the ICs without device overtemperature
shutdown. Because of the efficiency of the TAS5121I, heatsinks are smaller than those required for linear
amplifiers of equivalent performance.
R
θ JA
is a system thermal resistance from junction to ambient air. As such, it is a system parameter with roughly
the following components:
• R
θ JC
(the thermal resistance from junction to case, or in this case the metal pad)
• Heatsink compound thermal resistance
• Heatsink thermal resistance
The thermal grease thermal resistance can be calculated from the exposed pad area and the thermal grease
manufacturer's area thermal resistance (expressed in ° C-in
2
/W). The area thermal resistance of the example
thermal grease with a 0.001-inch-thick layer is about 0.054 ° C-in
2
/W. The approximate exposed pad area is as
follows:
36-pin PSOP3 0.116 in
2
Dividing the example thermal grease area resistance by the area of the pad gives the actual resistance through
the thermal grease for the device:
14