When flushing the firmware both USB-TTL and MicroUSB (or the power pins) need to be plugged in.
Since USB-TTL also offers 3v3 can we make use of that? Currently the VCC pin is unconnected.
Take the common red FT232RL as example:
6 GND
5 CTS - unconnected
4 VCC - unconnected
3 TX
2 RX
1 DTR