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P
Dmax +
2V2
DD
p 2
R
L
(11)
Θ
JA
+
1
Derating Factor
+
1
0.022
+ 45
°C W
(12)
T
A Max + TJ Max * ΘJA PD
+ 150 * 45(0.6
2) + 96°C (15dB crest factor)
(13)
TPA0312
SLOS335A – DECEMBER 2000 – REVISED OCTOBER 2004
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-
system, the internal dissipation in the TPA0312 and
maximum ambient temperatures is shown in Table 4.
Table 4. TPA0312 POWER RATING, 5-V, 3-
, STEREO
PEAK OUTPUT POWER
POWER DISSIPATION
MAXIMUM AMBIENT
AVERAGE OUTPUT POWER
(W)
(W/Channel)
TEMPERATURE(1)
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
85
°C
(1)
Package limited to 85
°C ambient
Table 5. TPA0312 POWER RATING, 5-V, 8-
, STEREO
POWER DISSIPATION
MAXIMUM AMBIENT
PEAK OUTPUT POWER
AVERAGE OUTPUT POWER
(W/Channel)
TEMPERATURE(1)
2.5 W
1250 mW (3-dB crest factor)
0.55
85
°C
2.5 W
1000 mW (4-dB crest factor)
0.62
85
°C
2.5 W
500 mW (7-dB crest factor)
0.59
85
°C
2.5 W
250 mW (10-dB crest factor)
0.53
85
°C
(1)
Package limited to 85
°C ambient
The maximum dissipated power, PDmax, is reached at a much lower output power level for a 3- load than for an
8-
load. As a result, this simple formula for calculating P
Dmax may be used for a 3- application:
However, in the case of an 8-
load, the P
Dmax 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 PDmax formula for
an 8-
load, but do not exceed the maximum ambient temperature of 85°C.
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 (see page 4). Converting 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 with the following equation. The maximum recommended junction temperature for the TPA0312 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 2.6-W system with 15-dB crest factor
per channel. Package limited to 85
°C
26