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Eric Raymond

CMod A7 Datasheet Warning


Looking at the CMod A7 to design into a CCA of my simulator. there is a warning in the datasheet that worries me

"Warning: When a USB host is attached to the Micro-USB connector, the VU pin on the DIP connector (pin 24) is driven to the voltage being provided by the USB host (typically between 4.5V-5.5V). If you have a power source attached to the VU pin, you must disconnect it before attaching a USB host, or risk damaging it. This can be particularly dangerous if the power source is a battery"

Does that indicate that I shouldn't plug into a powered CMod, or that I shouldn't power a Plugged in CMod.

I would like to only power the A7 with my power source, can I simply remove D1 to do this?

Second I want to use the FTDI chip, but it is nowhere in the schematic???

Last (for this morning) I cannot find any pin dimensions to design a model to plug it onto my board? I

Any help is appreciated



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Hi @Eric Raymond,

With regards to the first question, I would say it's best to go both ways (not plug into a powered Cmod and not power a plugged in Cmod), since you are relying on a single diode to prevent any back-powering problems that could arise (as opposed to a jumper setting to choose your power source).

You may be able to just remove the D1 and have it work out, though I don't know all of the ramifications with regards to powering the FTDI chip. You would also need to make sure any grounding between the input to the USB and the external power are connected to prevent voltage differences and issues there. However, if you are just wanting to power and have the Cmod A7 run a dedicated project, you can always load the flash on the Cmod A7 and every time the Cmod A7 is powered on it will automatically load the flash project. There are a couple of tutorials on this for the Cmod A7 Resource Center.

The schematic page for the FTDI chip (the "This page intentionally left blank" one) is proprietary. You can send an email to support dot digilent at ni dot com to request these details though.

We have a 3D model (.stp) for the Cmod A7 available on it's Resource Center on the right-hand side labeled as 3D STEP with a file name of cmod_a7.zip. There are some more dimensions about the Cmod A7 available on this thread as well.

Let me know if you have any questions.


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