TPA1517
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SLOS162D–MARCH 1997–REVISED FEBRUARY 2007
APPLICATION INFORMATION (continued)
3. If low frequency response is most important and depop is not a consideration then follow:
1
1
≤
≤ flow
2p60000 C
2pR C
I
L
I
THERMAL APPLICATIONS
Linear power amplifiers dissipate a significant amount of heat in the package under normal operating conditions.
A typical music CD requires 12 dB to 15 dB of dynamic headroom to pass the loudest portions without distortion
as compared with the average power output. Figure 19 shows that when the TPA1517 is operating from a 12-V
supply into a 4-Ω speaker that approximately 3.5 W peaks are possible. Converting watts to dB using the
following equation:
P
W
P
+ 10Log
ǒ Ǔ
dB
P
ref
3.5
+ 10Logǒ Ǔ
1
Subtracting dB for the headroom restriction to obtain the average listening level without distortion yields the
following:
(
)
5.44 dB * 15 dB + * 9.56 dB 15 dB headroom
(
)
5.44 dB * 12 dB + * 6.56 dB 12 dB headroom
Converting dB back into watts:
P
ń10
dB
P
+ 10
P
W
ref
+ 111 mW (15 dB headroom)
+ 221 mW (12 dB headroom)
This is valuable information to consider when attempting to estimate the heat dissipation requirements for the
amplifier system. Comparing the absolute worst cast, which is 3.5 W of continuous power output with 0 dB of
headroom, against 12-dB and 15-dB applications drastically affects maximum ambient temperature ratings for
the system. Using the power dissipation curves for a 12-V, 4-Ω system, internal dissipation in the TPA1517 and
maximum ambient temperatures are shown in Table 1.
Table 1. TPA1517 Power Rating
PEAK OUTPUT POWER
(W)
POWER DISSIPATION
(W/Channel)
MAXIMUM AMBIENT
TEMPERATURE
AVERAGE OUTPUT POWER
3.5
3.5
3.5
3.5
3.5
3.5
3.5 W
2.1
2.4
-34°C
-61°C
-48°C
-4°C
1.77 W (3 dB)
884 mW (6 dB)
442 mW (9 dB)
221 mW (12 dB)
111 mW (15 dB)
2.25
1.75
1.5
18°C
40°C
1.25
15
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