[SOLVED] FT232RL, entegrated LDO 3V3 regulator using PROBLEM

[elt42at]

HELLO TO EVERYONE!

I tried to use, BUS POWERED USB to UART with FT232RL. The design is so simple but, MY 3.3V output is over 4.2V. So, i re-solder 3V3 and VCCIO pins from PCB. I measured with AVO meter. The LDO output pin (3V3) is 3,26V. IT is OK! But THE VCCIO pin seems 4.4V!!!!!!

I soldered 3V3 pin to PCB, The VCC which goings to MCU VCC is about 3.3V. IT is ok!

Now, I have to solder the VCCIO pin to use FTDI FT232RL UART module in LVTTL 3.3V. I have to use VCCIO pin

I don't understand that, WHY an input (power input pin) makes the LDO output up to 4.2volt ????

I only use FT232RL pins RX,TX,CTS,RTS and CBUS0 and CBUS1 as RX/TX leds and CBUS2 as MCU reset, and CBUS3 MCU interrupt!!!

Please help me about that! I can't get integrated 3V3 output in the voltage 3.3V when i solder the VCCIO pin. It goings to 4.2V. Free un-soldered VCCIO pin seems over 4.4V. But it is an input pin !!!!

Thanks for your answers!

 

[sunil_n]

Hi,
try adding decoupling capacitors(10micro and 0.1micro farad) at the supply and VCCIO pins.looks like there is some noise issues

---------- Post added at 14:32 ---------- Previous post was at 14:16 ----------

HI,

refer the image, vbus is 5v

 

[elt42at]

YES, my schematics like that expect, my 3V3_LDO and VCCIO pins connected together! MY FTDI is working, UART working.... THE PROBLEM IS THAT WHEN VCCIO AND 3V3_OUT together, I measure 4.2V. When i re-solder VCCIO pin, The voltage is 3.25. I see 4.4V on VCCIO pin when it is free!!

 

[sunil_n]

bypass the VCC3O to ground through a 0.1micro farad capacitor and check the voltages

 

[elt42at]

Voltage is perfect! I pick-up VCCIO pin to free by re-soldering. The 3V3 is about 3.26V (fix)
I re-solder all pull-up resistors. Also, now there is 4.4V on VCCIO pin :S