How small can the GMSL1 link ac coupling capacitors be?

Maxim recommends using 0603 or larger 220nF capacitors for ac link coupling.  This is because for very small capacitors (0402 or smaller) the actual capacitance may be much less than the specified value at even a fraction of the rated voltage.  For instance, a 220nF 25V capacitor may be 100nF at 12V.  When it is important to use very small capacitors, make sure that the capacitance at the system operating voltage is at least 200nF.

For automotive systems in general, capacitors rated 50V should be used, so that faults shorting the GMSL1 coax to the battery do not cause cascade failures, however the normal operating voltage is zero.  For systems using Power over Coax (PoC aka Phantom Power), this dictates the capacitor rating.