TPA2001D1

1-W FILTERLESS MONO CLASS-D AUDIO POWER AMPLIFIER

SLOS338D – SEPTEMBER 2000 – REVISED DECEMBER 2002

5

POST OFFICE BOX 655303

APPLICATION INFORMATION

eliminating the output filter with the TPA2001D1

This section focuses on why the user can eliminate the output filter with the TPA2001D1.

effect on audio

The class-D amplifier outputs a pulse-width modulated (PWM) square wave, which is the sum of the switching

waveform and the amplified input audio signal. The human ear acts as a band-pass filter such that only the

frequencies between approximately 20 Hz and 20 kHz are passed. The switching frequency components are

much greater than 20 kHz, so the only signal heard is the amplified input audio signal.

traditional class-D modulation scheme

The traditional class-D modulation scheme, which is used in the TPA005Dxx family, has a differential output

0 volts across the load. The traditional class-D modulation scheme with voltage and current waveforms is shown

in Figure 1. Note that even at an average of 0 V across the load (50% duty cycle), the current to the load is high,

causing high loss, thus causing a high supply current.

0 V

–5 V

+5 V

Current

OUTP

Differential Voltage

Across Load

OUTN

Figure 1. Traditional Class-D Modulation Scheme’s Output Voltage and Current Waveforms Into an

Inductive Load With No Input

TPA2001D1 modulation scheme

The TPA2001D1 uses a modulation scheme that still has each output switching from 0 to the supply voltage.

However, OUTP and OUTN are now in phase with each other with no input. The duty cycle of OUTP is greater

than 50% and OUTN is less than 50% for positive voltages. The duty cycle of OUTP is less than 50% and OUTN

is greater than 50% for negative voltages. The voltage across the load sits at 0 V throughout most of the