Can I clock USB and I2S clock off same crystal - STM32F407VGT?

[MHunt.1]

Hi there,

I'm designing a PCB which will feed audio at 48KHz / 96KHz / 192KHz to a DAC over I2S (TI PCM5242).

I'd quite like the option to have USB - in an ideal world, USB Audio, but at the very least a COM port (USB device).

For the DAC, I'd need an HSE at 24.576MHz. For USB, I need something that can generate a precise 48MHz clock (right?)

Is there any way of doing this - the HSI isn't precise enough for either application? Do I need to move to a bigger pin count chip?

[waclawek.jan]

The 'F407 is a relatively old design with quite inflexible clocking scheme. You can use a "audio-friendly" external oscillator and input it directly through the I2S_CKIN pin.

Alternatively, user the fact that the DAC of your choice can generate the I2S clocks itself, and use the I2S in the 'F407 as slave. The DAC even has a fractional-N PLL.

JW

[Piranha]

The best helper for this is this:

http://www.alcula.com/calculators/math/simplify-fractions/