ZHCSJM6A April 2019 – October 2019 TAS6421-Q1
PRODUCTION DATA.
The thermally enhanced PowerPAD package has an exposed pad up for connection to a heat sink. The output power of any amplifier is determined by the thermal performance of the amplifier as well as limitations placed on it by the system, such as the ambient operating temperature. The heat sink absorbs heat from the TAS6421-Q1 and transfers it to the air. With proper thermal management this process can reach equilibrium and heat can be continually transferred from the device. Heat sinks can be smaller than that of classic linear amplifier design because of the excellent efficiency of class-D amplifiers. This device is intended for use with a heat sink, therefore, RθJC is used as the thermal resistance from junction to the exposed metal package. This resistance dominates the thermal management, so other thermal transfers are not considered. The thermal resistance of RθJA (junction to ambient) is required to determine the full thermal solution. The thermal resistance is comprised of the following components:
The thermal resistance of the thermal interface material can be determined from the manufacturer’s value for the area thermal resistance (expressed in °Cmm2/W) and the area of the exposed metal package. For example, a typical, white, thermal grease with a 0.0254 mm (0.001 inch) thick layer is approximately 4.52°C mm2/W. The TAS6421-Q1 in the DKQ package has an exposed area of 47.6 mm2. By dividing the area thermal resistance by the exposed metal area determines the thermal resistance for the thermal grease. The thermal resistance of the thermal grease is 0.094°C/W
Table 38 lists the modeling parameters for one device on a heat sink. The junction temperature is assumed to be 115°C while delivering and average power of 10 watts per channel into a 4 Ω load. The thermal-grease example previously described is used for the thermal interface material. Use Equation 3 to design the thermal system.
| Description | Value |
|---|---|
| Ambient Temperature | 25°C |
| Average Power to load | 10W |
| Power dissipation | 2W |
| Junction Temperature | 115°C |
| ΔT inside package | 1.8°C (0.9°C/W × 2W) |
| ΔT through thermal interface material | 0.188°C (0.094°C/W × 2W) |
| Required heat sink thermal resistance | 44.0°C/W ([115°C – 25°C – 1.8°C – 0.188°C] / 2W) |
| System thermal resistance to ambient RθJA | 45.1°C/W |