TPA2000D1Q1

2W FILTERLESS MONO CLASSD AUDIO POWER AMPLIFIER

SGLS137B− SEPTEMBER 2002 − REVISED SEPTEMBER 2004

10

POST OFFICE BOX 655303

APPLICATION INFORMATION

effects of applying a square wave into a speaker

Audio specialists have advised for years not to apply a square wave to speakers. If the amplitude of the

waveform is high enough and the frequency of the square wave is within the bandwidth of the speaker, the

square wave could cause the voice coil to jump out of the air gap and/or scar the voice coil. A 250-kHz switching

frequencies beyond the audio band. Therefore, the amount of cone movement at the switching frequency is

small. However, damage could occur to the speaker if the voice coil is not designed to handle the additional

power. To size the speaker for added power, the ripple current dissipated in the load needs to be calculated

efficiency

(1)

(2)

(3)

The maximum efficiency of the TPA2000D1 with an 8-

Ω load is 85%. Using Equation 3 with the efficiency at

maximum power (78%), we see that there is an additional 106 mW dissipated in the speaker. The added power

dissipated in the speaker is not an issue as long as it is taken into account when choosing the speaker.

when to use an output filter

Design the TPA2000D1 without the filter if the traces from amplifier to speaker are short. The TPA2000D1

passed FCC and CE radiated emissions with no shielding with speaker wires eight inches long or less. Notebook

PCs and powered speakers where the speaker is in the same enclosure as the amplifier are good applications

for class-D without a filter.

A ferrite bead filter (shown in Figure 11) can often be used if the design is failing radiated emissions without a

filter, and the frequency sensitive circuit is greater than 1 MHz. This is good for circuits that just have to pass

FCC and CE because FCC and CE only test radiated emissions greater than 30 MHz. If choosing a ferrite bead,

choose one with high impedance at high frequencies, but low impedance at low frequencies.

Use an output filter if the EMI sensitive circuits are low frequency (<1 MHz) and/or the leads from amplifier to

speaker are long.

The LC output filter is shown in Figure 11.

The ferrite filter is shown in Figure 11, where L is a ferrite bead.