Texas Instruments APA100 - Manual (Page 29)

TPA2001D1 (Class-D Modulator)
4-7 Technical Information
Figure 4−6. PSPICE Simulation of Open−Loop Response
f − Frequency − Hz
TAS5111
Output (dB)
Integrator
Output (dB)
200
100
−0
−100
−200
−300
100 1 k 10 k 100 k 1 M
Phase ( 5 )
4.2 TPA2001D1 (Class-D Modulator)
The TPA2001D1 was chosen as an excellent performance, low-cost analog
class-D modulator. A class-D modulator takes an analog input signal and
outputs a pulse width modulated (PWM) signal. The TPA2001D1 was selected
over other class-D amplifiers because of the following reasons.
1) Supply voltage range of 2.75 V to 5.5 V (matches up well with TAS5111
H-bridge).
2) Low noise (40
µ
V rms)
3) Low total harmonic distortion plus noise across 20 Hz to 20 kHz (<0.3%
over 20-Hz to 20-kHz frequency range)
4) Low cost (~$0.75 each in 1 kU)
The TPA2001D1 takes an analog input signal, gains it up, and compares it to
a 250-kHz triangle wave. The output of the comparator is a PWM signal. This
PWM signal is processed to make a differential signal, and it is sent to the
output MOSFETs. The TPA2001D1 outputs are capable of driving 1 W of
output power, but they are only driving high impedance in this case (the
TAS5111 inputs). The TPA2001D1 block diagram is shown in Figure 4−7.