TPA2001D2

1-W FILTERLESS STEREO CLASS-D AUDIO POWER AMPLIFIER

SLOS292A – MARCH 2000 – REVISED APRIL 2000

5

POST OFFICE BOX 655303

APPLICATION INFORMATION

eliminating the output filter with the TPA2001D2

This section will focus on why the user can eliminate the output filter with the TPA2001D2.

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 volts across the load (50% duty cycle), the current to the load is

high causing high loss thus causing a high supply current.

O V

–5 V

+5 V

Current

OUT+

Differential Voltage

Across Load

OUT–

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

Inductive Load With no Input

TPA2001D2 modulation scheme

The TPA2001D2 uses a modulation scheme that still has each output switching from 0 to the supply voltage.

However, OUT+ and OUT– are now in phase with each other with no input. The duty cycle of OUT+ is greater

than 50% and OUT– is less than 50% for positive voltages. The duty cycle of OUT+ is less than 50% and OUT–

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