On Fri, May 25, 2018 at 05:18:09PM +0200, Philipp Zabel wrote:
On Fri, 2018-05-25 at 15:52 +0100, Mark Brown wrote:
On Fri, May 25, 2018 at 01:42:53PM +0200, Marco Felsch wrote:
Also the formula for the delay time (t = C × 25,000/3.5) depends only on the capacity size.
Why not just have the user specify the capacitance of the capacitor on the rail which they can directly read from the schematic rather than forcing them to do the calcualtion? That seems a bit clearer and more user friendly (plus if someone decides the spec was wrong it's easier to roll out fixes).
The exact capacitance may not be known or vary above the nominal value because of cheap components, and the formula from the datasheet is just a guideline.
That variability is going to apply just as much to the charge time calculations/measurements as it is to the initial capacitance value - the results are going to be very much garbage in, garbage out.
I'd expect the usual method to set this delay to be semi-empirical: "start from the value calculated from datasheet and schematics and then increase until no more audio artifacts on a representative sample of boards". I think it is be better to specify a delay that works than a bogus capacitance value that happens to correspond to a delay that works.
If this is varying so drastically per board/system that it's relevant then we're already into problematic territory. For most devices we just have a number for the part, not something that varies so wildly that each system needs to configure it.