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CREST FACTOR AND THERMAL CONSIDERATIONS

P

dB +

10Log

P

W

P

ref

+ 10Log

4 W

1 W

+ 6 dB

(9)

P

W

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)

+ 2000 mW (15−dB crest factor)

(10)

TPA0312

SLOS335A – DECEMBER 2000 – REVISED OCTOBER 2004

A final point to remember about Class-AB amplifiers (either SE or BTL) is how to manipulate the terms in the

Class-AB 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 range, or headroom above the average power

output, to pass the loudest portions of the signal without distortion. In other words, music typically has a crest

factor between 12 dB and 15 dB. When determining the optimal ambient operating temperature, the internal

dissipated power at the average output power level must be used. From the TPA0312 data sheet, one can see

that when the TPA0312 is operating from a 5-V supply into a 3-

Ω speaker, 4-W peaks are available. Converting

watts to dB:

Subtracting the headroom restriction to obtain the average listening level without distortion yields:

•

6 dB - 15 dB = -9 dB (15-dB crest factor)

•

6 dB - 12 dB = -6 dB (12-dB crest factor)

•

6 dB - 9 dB = -3 dB (9-dB crest factor)

•

6 dB - 6 dB = 0 dB (6-dB crest factor)

•

6 dB - 3 dB = 3 dB (3-dB crest factor)

Converting dB back into watts:

25