TAS5112

SLES048C − JULY 2003 − REVISED MARCH 2004

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15

all cases. It is assumed that the thermal grease is 0.002

inch thick and that it is similar in performance to Wakefield

Type 126 thermal grease. It is important that the thermal

grease layer is

≤0.002 inches thick and that thermal pads

or tape are not used in the pad-to-heatsink interface due

to the high power density that results in these extreme

power cases.

Table 4. Case 1 (2

× 50 W Unclipped Into 6 Ω,

56-Pin HTSSOP

Ambient temperature

25

°C

Power to load (per channel)

50 W (unclipped)

Power dissipation

4.5 W

Delta T inside package

10.2

°C, note 2 ×

channel dissipation

Delta T through thermal grease

37.1

°C, note 2 ×

channel dissipation

Required heatsink thermal resistance

4.2

°C/W

Junction temperature

110

°C

System RθJA

19

°C/W

RθJA * power dissipation

85

°C

Junction temperature

85

°C + 25°C = 110°C

(1) This case represents a stereo system with only one package. See

Case 2 and Case 2A if doing a full-power, 2-channel test in a

multichannel system.

Table 5. Case 2 (2

× 50 W Unclipped Into 6 Ω,

56-Pin HTSSOP

Ambient temperature

25

°C

Power to load (per channel)

50 W (unclipped)

Power dissipation

4.5 W

Delta T inside package

5.1

°C

Delta T through thermal grease

18.6

°C

Required heatsink thermal resistance

6.9

°C/W

Junction temperature

110

°C

System RθJA

19

°C/W

RθJA * power dissipation

85

°C

Junction temperature

85

°C + 25°C = 110°C

(1) In this case, the power is separated into two packages. Note that

this allows a considerably smaller heatsink because twice as much

area is available for heat transfer through the thermal grease. For

this reason, separating the stereo channels into two ICs is

recommended in full-power stereo tests made on multichannel

systems.

Table 6. Case 2A (2

× 60 W Unclipped Into 6 Ω,

56-Pin HTSSOP

Ambient temperature

25

°C

Power to load (per channel)

60 W (10% THD)

Power dissipation per channel

5.4 W

Delta T inside package

6.1

°C, note 2 ×

channel dissipation

Delta T through thermal grease

22.3

°C, note 2 ×

channel dissipation

Required heatsink thermal resistance

5.3

°C/W

Junction temperature

110

°C

System RθJA

15.9

°C/W

RθJA * power dissipation

85

°C

Junction temperature

85

°C + 25°C = 110°C

(1) In this case, the power is also separated into two packages, but

overdriving causes clipping to 10% THD. In this case, the high

power requires extreme care in attachment of the heatsink to

ensure that the thermal grease layer is

≤ 0.002 inches thick. Note

that this power level should not be attempted with both channels in

a single IC because of the high power density through the thermal

grease layer.

Thermal

Pad

8,20 mm

7,20 mm

3,90 mm

2,98 mm