3.2 Use Case 2: Stereo Class D Amplifier with External Single-Ended Power Stage

Figure 3-6. Use Case 2 Schematic

The power buffer uses similar components in half-bridge and full-bridge configurations, so the choice of components is essentially the same. However, to prevent the DC component from damaging the loudspeaker, it is necessary in Single-Ended mode to introduce a capacitor (C_C) of relatively high value in series with the load.

Another significant difference, visible only in real-life waveforms, is that the Steady state (zero signal) of the amplifier in SE mode is a 50% duty cycle square wave at the oversampling frequency (768 kHz for 48 kHz multiple and sub-multiple input streams, and 705.6 kHz for 44.1 kHz multiples and sub-multiples), whereas the Steady state in Differential mode consists of alternating minimum width pulses from the P side and the N side. Consequently, in SE mode, there is a constant presence of high energy in the high-frequency carrier, which can heat and damage the transducer if it is not properly attenuated by a filter made of L_F and C_F.

The computations for C_C, L_F and C_F are described in Use Case 2 Output Filter Computation.