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P
D(max)
2V
2
DD
2
R
L
(11)
Θ
JA
1
Derating Factor
1
0.022
45
°
C
W
(12)
T
A
Max
T
J
Max
Θ
JA
P
D
150
45(0.6
2)
96
°
C (15-dB crest factor)
(13)
TPA6011A4
SLOS392A – FEBRUARY 2002 – REVISED JULY 2004
Table 6. TPA6011A4 Power Rating, 5-V, 3-
Ω
Stereo
PEAK OUTPUT POWER
POWER DISSIPATION
MAXIMUM AMBIENT
AVERAGE OUTPUT POWER
(W)
(W/Channel)
TEMPERATURE
4
2 W (3 dB)
1.7
-3
°
C
4
1 W (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 7. TPA6011A4 Power Rating, 5-V, 8-
Ω
Stereo
PEAK OUTPUT POWER
POWER DISSIPATION
MAXIMUM AMBIENT
AVERAGE OUTPUT POWER
(W)
(W/Channel)
TEMPERATURE
2.5
1250 mW (3-dB crest factor)
0.55
100
°
C
2.5
1000 mW (4-dB crest factor)
0.62
94
°
C
2.5
500 mW (7-dB crest factor)
0.59
97
°
C
2.5
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.
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. Use equation 12 to convert this to
θ
JA.
.
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 using Equation 13. The maximum recommended junction temperature for the TPA6011A4 is 150
°
C.
The internal dissipation figures are taken from the Power Dissipation vs Output Power graphs.
NOTE:
Internal dissipation of 0.6 W is estimated for a 2-W system with 15-dB crest factor per
channel.
Table 6 and Table 7 show that some applications require no airflow to keep junction temperatures in the
specified range. The TPA6011A4 is designed with thermal protection that turns the device off when the junction
temperature surpasses 150
°
C to prevent damage to the IC. Table 6 and Table 7 were calculated for maximum
listening volume without distortion. When the output level is reduced the numbers in the table change
significantly. Also, using 8-
Ω
speakers increases the thermal performance by increasing amplifier efficiency.
28
