CC2540 USB Question

Matt Kenyon2

Other Parts Discussed in Thread: CC2540

I'm using a CC2540 in my application and have a question concerning the power rails and USB communication. First, from reading other posts I have come to the conclusion that DVDD_USB needs to be connected to the same VDD source as all the other DVDD lines and not the USB power line.

My issue is I am supplying a VDD source of 2.3V off of a switcher and am wondering if USB communication will still operate if my VDD line remains 2.3V during USB communication?

over 12 years ago

0 Greenja over 12 years ago

Guru 22270 points

Hello Matt,

You could not connect the USB directly to the chip. As in the CC2540 USB Dongle, you would connect your USB 5+ to the input of your voltage regulator. From there you would supply the chip.

Thanks,

0 Matt Kenyon2 over 12 years ago in reply to Greenja

Prodigy 80 points

Yes, that is essentially what I had mentioned in my first sentence.

My question is if there is an opportunity for the Data+ and Data- lines from the USB to be greater than VDD (2.3V) during communication and if that would cause an issue.

Thanks,

0 Greenja over 12 years ago in reply to Matt Kenyon2

Guru 22270 points

Matt,

Without going into too much detail, the USB uses a voltage differential on D+ and D- for communication. D+ has to be pulled up for high speed USB as in the USB Dongle P1_0. With a differential voltage transmission, the actual signals, "1" and "0" is differentiated by 200mV.

You don't have to worry about the USB signals interfering with the controller.

Thanks,

0 Matt Kenyon2 over 12 years ago in reply to Greenja

Prodigy 80 points

That makes sense. I missed the pull up resistor in my initial design. Thank you.

0 Rui Code over 12 years ago in reply to Greenja

Prodigy 150 points

Hi Greenja,

I would like to know why there is P1_0 pin connect to USB D+

R32 and R92 are the pulled-up resistor for the D+, why we need to add the P1_0??

Thanks

0 Greenja over 12 years ago in reply to Rui Code

Guru 22270 points

Hello Rui,

That is a good question. Either R92 isn't populated or P1_0 would have to be set to 0V in order to disable the the USB.

From the BOM found in the CC2540 USB Design, SWRU072, it states in the excel spreadsheet that R92 is DO NOT MOUNT.

Thanks,

0 Rui Code over 12 years ago in reply to Greenja

Prodigy 150 points

Hi Greenja

Thanks

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CC2540 USB Question