How to handle DVDD_USB of CC2540 in self-powered mode?

Also, to where should the 1.5k pullup on D+ be tied in this situation?

Scott

Hello Scott,

The best solution would be to follow the reference design for the CC2540 Dongle. http://www.ti.com/lit/zip/swrr072

Thanks,

I looked at that before I posted my questions.  That reference design is for a bus-powered device, which doesn't help me given that we're doing a self-powered device.

Scott

The only difference between bus powered and self-powered is that the USB connector pin is not connected to the board.  Everything else remains the same.  You would tie your input voltage to the regulator to bring the voltage down to 3.3V.

Thanks,

A couple of things:

- You said "the USB connector pin is not connected to the board." Which of the USB connector pins are you talking about: VBUS?

- When you refer to "your input voltage", what voltage are you talking about?

Thanks,

Scott

Hello Scott,

I apologize for my lack of clarity in the last post.

Take a look at this app note.  Section 3.1.4 probable gives a better picture of what I was trying to explain.

http://datasheet.octopart.com/TPS2014D-Texas-Instruments-datasheet-10257340.pdf

Thanks,

I think I'm not being clear about exactly what I'm asking.  I understand how to provide power.  What I'm asking about is making sure the CC2540's USB block exhibits the correct behavior when it gets connected to a host, i.e. it enumerates properly, etc.  I don't know what it needs to do that, including whether or not DVDD_USB needs to cycle, for instance.

Thanks,
Scott

Hello Scott,

If you look at the powered schematic for the USB Dongle, you will see that P1_0  is used to indicate (possibly control) the presence of the USB signal for HS.  I can't remember if the USB code in the stack uses this signal for indicating that there is HS or for enabling HS,  I get it confused with another MCU often.  You can look through the USB code or perhaps it is in the CC USB Software Example Guide Swru222 http://www.ti.com/lit/pdf/swru222 to see exactly what that pin does in relation to the USB.

If you follow the circuit diagram and your 3.3V is present (supplied by battery or adapter), you should not see any difference in the USB performance from the powered version.  The firmware will behave the same way.

I hope that helps.

Thanks,

Indeed, I noticed that, and was wondering if it had to be P1_0 specifically.  That resistor indicates Full Speed, not High Speed, FYI.  I'll ask the firmware engineer to check the software to see if it tells us.  So you think I should just tie DVDD_USB to 3.3 V permanently and all will be well?

Thanks,
Scott

You could also post your question in the RF hardware Forum.  They may be able to provide a different explanation that helps you out better.

Thanks,

If you want to follow the USB specs to the letter, then you cannot tie it to your source VDD because you would allow current to be sourced when the host is turned off.

Take a look at this document and the self-powered options.

 http://www.ftdichip.com/Documents/AppNotes/AN232-08_01.pdf

Thanks,

I definitely would not attach my internal power the VBUS pin of the USB connector.  It sounds like I have to leave it floating, since the CC2540 doesn't appear to have a VBUS detection input, unlike some USB micros.

Scott