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I’ve been looking for a MCU/MPU with built-in Ethernet connectivity, and I’ve noticed that most only contain a built-in Ethernet MAC interface and require an external PHY.
Why is this the case, as in why do most of these chips not contain both a MAC and a PHY to minimize the number of additional ICs needed?
PHY requires some fairly beefy pin drivers as well as analog signal processing on the receive side. The fabrication processes to support this well are not optimized for high-density digital logic, which is what the MAC and the rest of the system require. The PHY also dissipates a significant amount of power all by itself. And sometimes different media require different PHYs, but the MAC can be the same. For all of these reasons, it makes sense to keep it as a separate chip.
That said, there are some chips targeted for embedded applications that include both. Wiznet, for one, has products in this space.
A company called Luminary made MCUs with both Ethernet MAC and PHY in one package, however they accomplished that by co-packaging two individual chips.
TI has since acquired them, not sure if they discontinued those particular parts in their entirety. They did discontinue some that we were using, sadly, with no pin-compatible replacements.
The IC processes required for the analog PHY functions and high density lower power digital are generally not well compatible. You'll see a somewhat similar separation of higher voltage/current I/O and of EEPROM memory, for similar reasons.
Multi-chip packages (outside of the memory arena) have become more popular with the relatively recent introduction of chiplets, so we could see more of this kind of thing, though wired Ethernet may not be as compelling as it was some years ago.
