Datasheet

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    
  
SLOS278D − JANUARY 2000 − REVISED NOVEMBER 2002
18
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
crest factor and thermal considerations (continued)
Converting dB back into watts:
P
W
+ 10
PdBń10
P
ref
+ 63 mW (18-dB crest factor)
+ 125 mW (15-dB crest factor)
+ 250 mW (9-dB crest factor)
+ 500 mW (6-dB crest factor)
+ 1000 mW (3-dB crest factor)
(12)
+ 2000 mW (15-dB crest factor)
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. Table 3 shows maximum ambient temperatures and TPA0233 internal power dissipation for various
output-power levels.
Table 3. TPA0233 Power Rating, 5-V, 3-Ω, Mono
PEAK OUTPUT POWER
(W)
AVERAGE OUTPUT POWER
POWER DISSIPATION
(W)
MAXIMUM AMBIENT
TEMPERATURE
4 2 W (3-dB crest factor) 1.7 −3°C
4 1000 mW (6-dB crest factor) 1.6 6°C
4 500 mW (9-dB crest factor) 1.4 24°C
4 250 mW (12-dB crest factor) 1.1 51°C
4 125 mW (15-dB crest factor) 0.8 78°C
4 63 mW (18-dB crest factor) 0.6 96°C
Table 4. TPA0233 Power Rating, 5-V, 8-Ω, Stereo
PEAK OUTPUT POWER
(W)
AVERAGE OUTPUT POWER
POWER DISSIPATION
(W)
MAXIMUM AMBIENT
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
Dmax
), is reached at a much lower output power level for an 8-Ω load than
for a 4-Ω load. As a result, this simple formula for calculating P
Dmax
may be used for a 4-Ω application.
P
Dmax
+
2V
2
DD
p
2
R
L
(13)
However, in the case of a 4-Ω 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 P
Dmax
formula
for a 4-Ω load.
The maximum ambient temperature depends on the heat sinking ability of the PCB system. The derating factor
for the DGQ package is shown in the dissipation rating table. Converting this to Θ
JA
:
Θ
JA
+
1
Derating Factor
+
1
0.0171
+ 58.48°CńW
(14)