TPA721

700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER

SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000

18

POST OFFICE BOX 655303

APPLICATION INFORMATION

5-V versus 3.3-V operation

The TPA721 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 TPA721 can produce a maximum

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 than 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 TPA721 data sheet, one can see that when the TPA721

is operating from a 5-V supply into a 8-

Ω speaker that 700 mW peaks are available. Converting watts to dB:

P

dB +

10 Log P

W +

10Log 700 mW

+ –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 +

10PdB 10

+ 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)