I'm having problems with a custom FT232RL board. I've designed lots of FT232-based boards in the past, but always with an additional LDO to power my MCU from Vbus (5V). This time I want the FT232RL to power my MCU from its internal 3.3V LDO but voltage at the VCCIO and 3V3OUT pins is higher than that:
With my MCU board unplugged: VCCIO = 3.3VOUT = 4.1 V
With my MCU board plugged: VCCIO = 3.3VOUT = 3.8 V
Apart from this issue, the board is working well (USB comms, UART comms, LED's, etc).
This is my circuit:
100nF decoupling capacitors are close to VCCIO and 3V3OUT pins. Additionally, I've tried placing some other values like 10uF and 1uF but nothing changes.
FYI, I've found where the problem is. My FTDI IC's where bought from an eBay store, all showing a ref number "0550-A". Well none of these chips are able to regulate to 3.3V. Using new FT232RL IC's purchased from Mouser solved the problem.