SA7269

HANGZHOU SILAN MICROELECTRONICS CO.,LTD

REV:1.2

2006.05.25

Http: www.silan.com.cn

Page 5 of 11

package varies with the mounting method used. A metal-to-metal interface will be about 1

°C /W if lubricated, and

about 1.2

°C /W if dry.

If a mica insulator is used, the thermal resistance will be about 1.6

°C /W lubricated and 3.4°C /W dry. For this

example, we assume a lubricated mica insulator between the SA7269 and the heat sink. The heat sink thermal

resistance must then be less than:

8.7

°C/W-2°C/W-1.6°C/W 5.1°C/W

The thermal requirements can become more difficult when an amplifier is driving a reactive load. For a given

magnitude of load impedance, a higher degree of reactance will cause a higher level of power dissipation within

the amplifier. As a general rule, the power dissipation of an amplifier driving a 60º reactive load (usually

considered to be a worst-case loudspeaker load) will be roughly that of the same amplifier driving the resistive

part of that load. For example, a loudspeaker may at some frequency have an impedance with a magnitude of 8

Ω

and a phase angle of 60º. The real part of this load will then be 4

Ω, and the amplifier power dissipation will

roughly follow the curve of power dissipation with a 4

Ω load.