FTDI chip power and connection issue (FTDI232HL)

Thread Starter

paul.scaccia

Joined Jun 26, 2019
2
I have a simple design using the FTDI FT232HL chip. If you are not familiar it is a "Single Channel HiSpeed USB to Multipurpose UART/FIFO IC."

I am having an issue where my 3.3V rail looks like the following below. With this, I do not get a virtual COM port connection to the PC.

sd.png

I have the power supplies, internal LDO’s and USB connector hooked up the following.
asdef.png


dfgh.jpg hjgmh.png

Please let me know of any issues you see or any potential causes I can check.

When I connect a USB isolator, namely the Keterex KX USB-150, the 3.3V rail becomes solid and then I get the COM port showing on my PC.

Thoughts?
 

Picbuster

Joined Dec 2, 2013
1,020
I have a simple design using the FTDI FT232HL chip. If you are not familiar it is a "Single Channel HiSpeed USB to Multipurpose UART/FIFO IC."

I am having an issue where my 3.3V rail looks like the following below. With this, I do not get a virtual COM port connection to the PC.

View attachment 212377

I have the power supplies, internal LDO’s and USB connector hooked up the following.
View attachment 212380


View attachment 212378 View attachment 212379

Please let me know of any issues you see or any potential causes I can check.

When I connect a USB isolator, namely the Keterex KX USB-150, the 3.3V rail becomes solid and then I get the COM port showing on my PC.

Thoughts?
First glance it looks good however: I always use a multifuse 0,2A and diode to protect my system (usb cable or stick shortcut) in l3 circuit.

Picbuster
 

DickCappels

Joined Aug 21, 2008
6,542
Could be a grounding issue, at least that is what the results of the isolator experiment suggests. What is the UART side of the circuit connected to and how is it grounded with respect to the scope?
 

Thread Starter

paul.scaccia

Joined Jun 26, 2019
2
Could be a grounding issue, at least that is what the results of the isolator experiment suggests. What is the UART side of the circuit connected to and how is it grounded with respect to the scope?
Hi there, thank you for the response. UART Side is the PC and it is a laptop powered by the wall and grounded by the wall. Scope is also grounded by the wall. If I disconnect the laptop from the wall, I have the same results. One thing to note, my D+/D- are not perfect differential traces, but they are relatively short and the trace length difference was negligible based on some googling... an isolator wouldn't "repair" a dirty differential pair would it?
 

DickCappels

Joined Aug 21, 2008
6,542
It might clean up the signals and re-sync them to the clock. It depends on how good the designers wanted to make it.

Are you sure that the bump on your 3.3 volts is the reason you don't find the virtual COM port? If you are running in high speed mode (480 Mb/S) then it will pay to be very careful with your traces. This is RF!

If it is 12 Mb/S you can be a little more relaxed.
 
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