Datasheet


SLOS386A − NOVEMBER 2001 − REVISED APRIL 2007
23
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APPLICATION INFORMATION
crest factor and thermal considerations (continued)
This is valuable information to consider when attempting to estimate the heat dissipation requirements for the
amplifier system. Comparing the absolute worst case, which is 2 W of continuous power output with a 3 dB crest
factor, against 12 dB and 15 dB applications drastically affects maximum ambient temperature ratings for the
system. Using the power dissipation curves for a 5-V, 3-Ω system, the internal dissipation in the TPA6017A2
and maximum ambient temperatures is shown in Table 3.
Table 3. TPA6017A2 Power Rating, 5-V, 3-Ω, Stereo
PEAK OUTPUT POWER
(W)
AVERAGE OUTPUT POWER
POWER DISSIPATION
(W/Channel)
MAXIMUM AMBIENT
TEMPERATURE
4 2 W (3 dB) 1.7 −3°C
4 1000 mW (6 dB) 1.6 6°C
4 500 mW (9 dB) 1.4 24°C
4 250 mW (12 dB) 1.1 51°C
4 125 mW (15 dB) 0.8 78°C
4 63 mW (18 dB) 0.6 96°C
Table 4. TPA6017A2 Power Rating, 5-V, 8-Ω, Stereo
PEAK OUTPUT POWER AVERAGE OUTPUT POWER
POWER DISSIPATION
(W/Channel)
MAXIMUM AMBIENT
TEMPERATURE
2.5 W 1250 mW (3 dB crest factor) 0.55 100°C
2.5 W 1000 mW (4 dB crest factor) 0.62 94°C
2.5 W 500 mW (7 dB crest factor) 0.59 97°C
2.5 W 250 mW (10 dB crest factor) 0.53 102°C
The maximum dissipated power, P
D(max)
, is reached at a much lower output power level for an 8-Ω load than
for a 3-Ω load. As a result, this simple formula for calculating P
D(max)
may be used for an 8-Ω application:
P
D(max)
+
2V
2
DD
p
2
R
L
(9)
However, in the case of a 3-Ω load, the P
D(max)
occurs at a point well above the normal operating power level.
The amplifier may therefore be operated at a higher ambient temperature than required by the P
D(max)
formula
for a 3-Ω load.
The maximum ambient temperature depends on the heat sinking ability of the PCB system. The derating factor
for the PWP package is shown in the dissipation rating table. Converting this to Θ
JA
:
(10)
Θ
JA
+
1
Derating Factor
+
1
0.022
+ 45°CńW
To calculate maximum ambient temperatures, first consider that the numbers from the dissipation graphs are
per channel so the dissipated power needs to be doubled for two channel operation. Given Θ
JA
, the maximum
allowable junction temperature, and the total internal dissipation, the maximum ambient temperature can be
calculated with the following equation. The maximum recommended junction temperature for the TPA6017A2
is 150°C. The internal dissipation figures are taken from Figure 26.