TPA731 Datasheet, PDF (19/22 Pages) Texas Instruments – 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS

TPA731
700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER
WITH DIFFERENTIAL INPUTS
SLOS315B – JUNE 2000 – REVISED OCTOBER 2002
APPLICATION INFORMATION
headroom and thermal considerations
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. From the TPA731 data sheet, one can see that when the TPA731
is operating from a 5-V supply into an 8-Ω speaker that 700 mW peaks are available. Converting watts to dB:
PdB
+
10 Log
PW
Pref
+
10Log
700
1
mW
W
+
–1.5
dB
Subtracting the headroom restriction to obtain the average listening level without distortion yields:
–1.5 dB – 15 dB = –16.5 (15 dB headroom)
–1.5 dB – 12 dB = –13.5 (12 dB headroom)
–1.5 dB – 9 dB = –10.5 (9 dB headroom)
–1.5 dB – 6 dB = –7.5 (6 dB headroom)
–1.5 dB – 3 dB = –4.5 (3 dB headroom)
Converting dB back into watts:
P_W + 10^PdBń10 x Pref
= 22 mW (15 dB headroom)
= 44 mW (12 dB headroom)
= 88 mW (9 dB headroom)
= 175 mW (6 dB headroom)
= 350 mW (3 dB headroom)
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 700 mW 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 5-V, 8-Ω system, the internal dissipation in the TPA731
and maximum ambient temperatures is shown in Table 2.
Table 2. TPA731 Power Rating, 5-V, 8-Ω, BTL
PEAK OUTPUT
POWER
(mW)
AVERAGE OUTPUT
POWER
POWER
DISSIPATION
(mW)
D PACKAGE
(SOIC)
MAXIMUM AMBIENT
TEMPERATURE
DGN PACKAGE
(MSOP)
MAXIMUM AMBIENT
TEMPERATURE
700
700 mW
675
700
350 mW (3 dB)
595
700
176 mW (6 dB)
475
700
88 mW (9 dB)
350
700
44 mW (12 dB)
225
34°C
47°C
68°C
89°C
111°C
110°C
115°C
122°C
125°C
125°C
Table 2 shows that the TPA731 can be used to its full 700-mW rating without any heat sinking in still air up to
110°C and 34°C for the DGN package (MSOP) and D package (SOIC) respectively.
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
19