Hi All,

I am puzzled and so wanted to reach out.

I have a PCB design which uses the FTDI FT232RL as a UART-USB bridge.

I just populated 7 PCB's (same layout, batch, board house etc) and found two of them fail to enumerate the device when connected to the USB on my PC. In device manager the USB port shows Unknown USB Device (Device Descriptor Request Failed).

I suspected a damaged chip so replaced it on on of the boards (twice) taking the utmost ESD precautions. Still the same behaviour.

Its unlikely to be a driver issue as i can swap to a good board and it will enumerate just fine. The problem appears to be in hardware.

There are no shorts on open connections on the board.

Anybody had a similar experience or any suggestions?

Many thanks

Ade

 

Show us your PCB layout, both sides, top and bottom. Maybe it has something to do with your layout.
Did you install proper decoupling capacitors as recommended in the datasheet?

 

Did you get your ICs from a reputable source, or could they be fakes/clones?

 

I've used that chip before, is it a stand alone chip or a module that you're using?

 

Hi All,

many thanks for the active response. This was my first post in AAC and good that know that support is out there.

In principle i did follow the guidelines in the datasheet (components selection and design). I sourced the chips from DigiKey and Farnell. I read too about the issue with the fake versions.

I actually reached out to FTDI directly on this issue and they have been very responsive requesting more information.
I have provided them more technical background and am looking forward to their feedback.

I see a couple of potential issues.

My D+ and D- lines run from one PCB to another via a connector. This could be an issue.

On one of the PCB (although mostly quite parallel traces) my D+ line is 10mm longer than my D- line. Another potential issue.

I attach an extract from the email content I sent to FTDI. I would still be grateful if anyone is willing to take a glance.

Once i resolve this, i will for certain update this thread with the fix such that i can disseminate my learnings to the masses.

Many thanks

Ade

 

I see a couple of potential issues.

My D+ and D- lines run from one PCB to another via a connector. This could be an issue.

On one of the PCB (although mostly quite parallel traces) my D+ line is 10mm longer than my D- line. Another potential issue.

That is something I would never do. My traces from the USB connector to the USB controller are parallel and kept to the minimum, no more than 10mm total, no interconnect to another PCB.

 

Hi All,

I am puzzled and so wanted to reach out.

I have a PCB design which uses the FTDI FT232RL as a UART-USB bridge.

I just populated 7 PCB's (same layout, batch, board house etc) and found two of them fail to enumerate the device when connected to the USB on my PC. In device manager the USB port shows Unknown USB Device (Device Descriptor Request Failed).

I suspected a damaged chip so replaced it on on of the boards (twice) taking the utmost ESD precautions. Still the same behaviour.

Its unlikely to be a driver issue as i can swap to a good board and it will enumerate just fine. The problem appears to be in hardware.

There are no shorts on open connections on the board.

Anybody had a similar experience or any suggestions?

Many thanks

Ade

I used the FTDI chip and vinculum . I use the FTDI tool to see if chip is working ( available @ their site). The driver is could give some problems like 'it does install but won't work' use the common driver as specified by FTDI (CDM v2.12.06 WHQL Certified).
The tool allows you to find and modify serial number and suppliers name.
good luck
Picbuster