APA2057A
Application Information (Cont.)
Thermal Considerations (Cont.)
Package
TSSOP-28
qJA
°
45 C/W
TQFN -28
°
43 C/W
Table 4: Thermal resistance Table
This parameter is measured with the recommended
copper heat sink pattern on a 2-layer PCB, 23cm2
in 5.7mm *4mm in PCB, 2oz. Copper, 100mm2
coverage. Airflow 0 CFM the maximum ambient tem-
perature depends on the heat sink ability of the PCB
system.
To calculate maximum ambient temperatures, first
consideration is that the numbers from the dissipation
graphs are per channel values, so the dissipation of the
IC heat needs to be doubled for two-channel operation.
Given qJA, the maximum allowable junction temperature
(TJ,Max), and the total intemal dissipation (PD), the maximum
ambient temperature can be calculated with the following
equation. The maximum recommended junction
temperature for the APA2057A is 150°C. The internal
dissipation figures are taken from the Power Dissipation
vs. Output Power graph.
TA,Max = TJ,Max - qJAPD
(11)
150 - 45(0.8*2) = 78°C (with thermal pad)
NOTE: Internal dissipation of 0.8W is estimated for a 2W system
with 15-dB headroom per channel.
Table 3 shows that for some applications, no airflow is
required to keep junction temperatures in the specified
range. The APA2057A is designed with a thermal shut-
down protection that turns the device off when the junction
temperature surpasses 150°C to prevent IC from
damage. The information in table 3 was calculated for
maximum listen volume with limited distortion. When
the output level is reduced, the numbers in the table
change significantly. Also, using 8W speakers will dra-
matically increase the thermal performance by increasing
amplifier efficiency.
Copyright ã ANPEC Electronics Corp.
26
www.anpec.com.tw
Rev. A.1 - Aug., 2007
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
