TPA005D02

2-W STEREO CLASS-D AUDIO POWER AMPLIFIER

SLOS227C – AUGUST 1998 – REVISED MARCH 2000

21

POST OFFICE BOX 655303

APPLICATION INFORMATION

crest factor and thermal considerations

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 TPA005D02 data sheet, one can see that when the

TPA005D02 is operating from a 5-V supply into a 4-

Ω speaker that 4 W peaks are available. Converting Watts

to dB:

P

P

W

P

ref

+ 10Log 4

1

+ 6dB

(17)

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

6.0 dB

* 15 dB +* 9dB (15 dB crest factor)

6.0 dB

* 12 dB +* 6dB (12 dB crest factor)

6.0 dB

* 9dB +* 3dB (9 dB crest factor)

6.0 dB

* 6dB +* 0dB (6 dB crest factor)

6.0 dB

* 3dB + 3dB (3 dB crest factor)

6.0 dB

* 18 dB +* 12 dB (15 dB crest factor)

Converting dB back into watts:

P

PdB 10

P

ref

+ 125 mW (15 dB crest factor)

+ 250 mW (12 dB crest factor)

+ 500 mW (9 dB crest factor)

+ 1000 mW (6 dB crest factor)

+ 2000 mW (3 dB crest factor)

(18)

+ 63 mW (18 dB crest factor)

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 2 W of continuous power output with a 3 dB crest

factor, 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, 4-

Ω system, the internal dissipation in the TPA005D02

and maximum ambient temperatures is shown in Table 4.