7.3 Power Amplifier
This application uses a custom-made Class D power amplifier (Figure 7-3) to connect an external speaker to the DAC output. A 300 kHz, 95% duty cycle PWM signal is used to generate a sawtooth waveform. This sawtooth waveform, along with the DC-offset DAC signal, is fed into a comparator to generate a PWM waveform. This PWM waveform passes through a MOSFET driver to drive an externally connected speaker. Refer to the TC4426/TC4427/TC4428 data sheet for more information about the MOSFET driver. This Class D power amplifier is implemented as a custom-made circuit on a PROTO Click Board™ (see Figure 7-5 and Figure 7-6).
In addition to the power amplifier, the PROTO Click Board™ also
contains the following additional features:
- An additional switch SW1 to access Passthrough mode.
- Jumper J1 to select the audio input source between Mic Click and Headphone Mic (1, 2).
- Jumper J2 to select the audio output between external speaker and 3.5 mm audio connector. The 3.5 mm audio connector can be used to connect to an external speaker or a headphone.
- Signal conditioning circuit for headphone microphone input. See Figure 7-4.
Important:
- The user is advised to select Mic Click as audio input source when a headphone microphone is not connected.
- It is recommended to avoid selecting headphones for both audio output and mic input together in Passthrough mode to avoid noise induction.