Question: I am designing an audio amplifier using the TPA5710 for an application that requires a power supply to drive 25W per channel into an 8R load. I also need 3.3V for my system logic and 12V to support a couple of "special purpose" amplifiers. If I add additional taps to my SMPS power transformer, where do I connect my regulation loop sensing. I understand that the most common method is to connect regulation to the highest current load; however, that will be the main supply to the amplifier (PVDD) and audio has a crest factor (it has current surges) so my other voltages will be basically unregulated.
Answer: Yes, you are correct your 3.3V and 12V will be unregulated and fluctuate with the current load drawn by the amplifier. A good method for generating your 3.3V and 12V is to use buck converters and driven from the main amplifier supply. By doing this, all three of your voltages will be regulated and you will simplify your SMPS power transformer.
A good buck converter to consider is the TPS40400 from Texas Instruments.