My customer asks:
"First, in regards to the PSEL pin, is that pin only connected to the configuration discriptor used be the host when determining max power allowable? I ask because I am using this chip in self powered mode in order to get lower THD from an external LDO but the entire circuit is still powered by the USB 5V input. If this chip is telling the host that it will only draw 100mA then that would be bad because I am using about 200mA with peaks going all the way up to 500mA. My computer seems to ignore the power limits no matter what device I plug in which works for me but maybe a customer will have a system that does not ignore the limits programmed in software.
Can I set PSEL high while not using the internal LDO? The diagram on page 8 of the datasheet (SLES081F) does not show any connections but then those diagrams are never meant to show you everything inside the chip so I must ask. The LDO appears to be rather standalone and if not used, the proper thing to do is just connect its inputs and outputs to the same voltage level.
Second, do you have any document that describes the parts and values chosen on the output pins VOUTL and VOUTR? The specs say that distortion numbers are dependent on these parts and value selections so I would really like to tune it to my own circuit if possible. I attach these audio outputs to a non-inverting preamp stage so right now I use the example in the datasheet that drives a class-D amp (page 28). It works but if I can make it better, I would. With a high impedance input, are those 100uF capacitors a bit excessive for filtering? If they work like I think they would (maybe not with all those other parts all around it), that large of a cap would create a high pass filter of well under 1Hz. I'm also having a bit of an issue with popping on the speakers when the system powers up and if I knew how to safely tweak these parts, I could determine what is doing it.
Also if you have any more detailed application documents available about component selection in the output section for line level applications, it would help me understand the part choices I should use in the final design. I’m attempting to create a high end audio amplifier device and don’t want to make any sub par choices by just copying the reference design."