I'm trying to wire up my first device using an FTDI USB to Serial converter. FTDI recommends not mixing bus and self powered designs. But they also mention that it's possible in the documentation. My current design will be mostly self powered but will connect to a PC for data dumps and charging (200mA). It will be powered from a single cell LiPo and has some protection circuitry to prevent over discharging.
What I suspect might be a problem is USB suspend mode, which states that if no data is transferred for a set period the USB device should reduce power. Since most of my design operates from 3V, I want the FT230X to interface from this level as well. VBAT is guaranteed to always be 3.3V - 4.2V. Below is what I have so far, the idea was that configuring CBUS3 as a keep_awake that would prevent it from going to sleep (as I understand it), this would cause it to always be active though, even when self powered:
So my question is this, how do I implemented a bus and self powered device that can drain 200mA from the host for charging even when no data is being transferred?
