TAS5112DFD datasheet(14/19 Pages) TI

14 / 19 page

TAS5112

SLES048C − JULY 2003 − REVISED MARCH 2004

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Another parameter to be considered is the idle current loss

in the inductor. This can be measured or specified as

inductor dissipation (D). The target specification for

dissipation is less than 0.05.

In general, 10-

µH inductors suffice for most applications.

The frequency response of the amplifier is slightly altered

by the change in output load resistance; however, unless

tight control of frequency response is necessary (better

than 0.5 dB), it is not necessary to deviate from 10

µH.

The graphs in Figure 12 display the inductance vs current

characteristics of two inductors that are recommended for

use with the TAS5112.

Figure 12. Inductance Saturation

I − Current − A

INDUCTANCE

CURRENT

DFB1310A

DASL983XX−1023

The selection of the capacitor that is placed across the

output of each inductor (C2 in Figure 11) is simple. To

complete the output filter, use a 0.47-

µF capacitor with a

voltage rating at least twice the voltage applied to the

output stage (PVDD).

This capacitor should be a good quality polyester dielectric

such as a Wima MKS2-047ufd/100/10 or equivalent.

In order to minimize the EMI effect of unbalanced ripple

loss in the inductors, 0.1-

µF 50-V SMD capacitors (X7R or

better) (C1A and C1B in Figure 11) should be added from

the output of each inductor to ground.

THERMAL INFORMATION

The thermally augmented package provided with the

TAS5112 is designed to be interfaced directly to heatsinks

using a thermal interface compound (for example,

Wakefield Engineering type 126 thermal grease.) The

heatsink then absorbs heat from the ICs and couples it to

the local air. If the heatsink is carefully designed, this

process can reach equilibrium and heat can be continually

removed from the ICs. Because of the efficiency of the

TAS5112, heatsinks can be smaller than those required for

linear amplifiers of equivalent performance.

RθJA is a system thermal resistance from junction to

ambient air. As such, it is a system parameter with roughly

the following components:

D RθJC (the thermal resistance from junction to

case, or in this case the metal pad)

D Thermal grease thermal resistance

D Heatsink thermal resistance

RθJC has been provided in the General Information

section.

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-in2/W). The area thermal resistance of the example

thermal grease with a 0.002-inch thick layer is about 0.1

°C-in2/W. The approximate exposed pad area is as

follows:

56-pin HTSSOP

0.045 in2

Dividing the example thermal grease area resistance by

the surface area gives the actual resistance through the

thermal grease for both ICs inside the package:

56-pin HTSSOP

2.27

°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.

Neither pads nor tape should be used with either of these

two packages. A thin layer of thermal grease with careful

clamping of the heatsink is recommended. It may be

difficult to achieve a layer 0.001-inch thick or less, so the

modeling below is done with a 0.002-inch thick layer,

which may be more representative of production thermal

grease thickness.

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 RθJA = RθJC +

thermal-grease resistance + heatsink resistance.

Table 4,

Table 5, and

Table 6 indicate modeled

parameters for one or two TAS5112 ICs on a single

heatsink. The final junction temperature is set at 110

°C in

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