Datasheet
SLOS230D − NOVEMBER 1998 − REVISED OCTOBER 2002
28
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
5-V versus 3.3-V operation
The TPA711 operates over a supply range of 2.5 V to 5.5 V. This data sheet provides full specifications for 5-V
and 3.3-V operation, as these are considered to be the two most common standard voltages. There are no
special considerations for 3.3-V versus 5-V operation with respect to supply bypassing, gain setting, or stability.
The most important consideration is that of output power. Each amplifier in TPA711 can produce a maximum
voltage swing of V
DD
− 1 V. This means, for 3.3-V operation, clipping starts to occur when V
O(PP)
= 2.3 V as
opposed to V
O(PP)
= 4 V at 5 V. The reduced voltage swing subsequently reduces maximum output power into
an 8-Ω load before distortion becomes significant.
Operation from 3.3-V supplies, as can be shown from the efficiency formula in equation 4, consumes
approximately two-thirds the supply power of operation from 5-V supplies for a given output-power level.
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 TPA711 data sheet, one can see that when the TPA711
is operating from a 5-V supply into a 8-Ω speaker that 700 mW peaks are available. Converting watts to dB:
P
dB
+ 10Log
ǒ
P
W
P
ref
Ǔ+ 10Log
ǒ
700 mW
1W
Ǔ
+ –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
P
ref
+ 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)