I've been thinking some more about the TTL (as opposed to the RS-232) variant. The TTL variant is designed to have the traditional 6 pin SIP header output.

Many traditional FTDI style interfaces just connect the Vcc output pin directly up to the output, which in principle violates the USB specification, as you're not allowed to draw significant current before the host has properly enumerated the device.

The fix for this is to switch the Vcc pin on and off with a MOSFET driven by the !POWER pin of the UART. In addition to this, an AP2331 current limiting switch can be used to protect the UART and the host from inrush or other problems. Since the CY7C65213 doesn't run internally at 3.3 volts, if we want to provide 3.3 volt functionality, we'd need to add an LDO. That's actually just as well, since we want to support up to 200 mA of supply current from the Vcc pin. Because of that, we'll specify in the bus enumeration parameters that we require up to 250 mA of bus current. You can do this using Cypress Semi's configuration utility (it's part of their SDK for Windows).

Anyway, take a look at the schematic in the PDF and let me know what you think.