• State TI Thinks Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 1 answer
  • Subscribers 52 subscribers
  • Views 915 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

CC2540 USB enabling

Mario Hernandez
Intellectual 695 points
Other Parts Discussed in Thread: CC2540, CC2544

Hello all,

The way the reference design explains how to connect the USB lines to the CC2540 is: connecting the line USB_DP+ to P1_0/LED line from the MCU through a 1K5 resistor. 

For my application I would like to connect P1_0/LED to Vbus instead of to USB_DP+. Can I do that? do you see any issue here?

Obviously I would use a voltage divider in between.

Many thanks

  • 0
    TI__Genius 9325 points
    Hi Mario,

    I will check this with a hardware expert.

    - Cetri
  • 0
    TI__Guru 56590 points

    Hello Mario,
    No problem, but keep the pull-up on the D+ line. Please note that this will mean that you will have a constant current draw from the USB Host which could have some impact on your average current consumption requirements.

    Correction:

    No you should not connect to Vbus as this has a voltage of around 5 V which would violate the absolute maximum rating for voltage applied to any digital pin (see page 4 in the CC2540 Data Sheet).You can instead place the LED to the output of the DC-DC (which convert from 5 V to CC2540 supply voltage).


    More info here:
    e2e.ti.com/.../1492750

  • 0 in reply to Cetri
    TI__Guru 56590 points
    Please note that I initially gave you an incorrect answer. The post have been corrected.
  • 0 in reply to Eirik V
    Intellectual 695 points

    No problem Eirik. Regarding that, please that I already mentioned that in my first post: "Obviously I would use a voltage divider in between".

    So the MCU would detect the USB with a 2.5 V, instead of the 5 V from the Vbus line. In fact I would move the connection D+ --- P1_0 to Vbus --- P1_0, pull up included.

    I need to verify if that way can work

    Many thanks

    Mario

  • 0 in reply to Eirik V
    Intellectual 695 points
    There is a pending reply (I edited it after replying) but anyway: I am not sure that connecting D+ to a pull-up on the MCU side is necessary. Other makers don't use the pull up and haven't seen any issue. From the host perspective, is it really required?
    What I would really need to do is substituting D+ --- P1_0 by Vbus --- P1_0, pull-up included

    Thanks again Eirik
    Mario
  • 0 in reply to Mario Hernandez
    TI__Guru 56590 points
    Hello Mario,
    In the case of using a voltage divider you will have an additional current leakage through the voltage divider, but if you connect to the chip supply you will not have that.

    Some other parts have an internal pull-up resistor embedded in the chip it self. As an example the CC2544 has this (CC2540 has not). The pull-up is a requirement from the USB specification to bias the bus correctly.
  • 0 in reply to Eirik V
    Intellectual 695 points
    Eirik,
    Regarding the leak, you're right, although when USB is plugged, that is not a big issue.
    As per the USB line itself and for coming to a conclusion: all rite, so that is something mandatory, whatever I change, I have to keep the D+ line connected to a pull up resistor, right?

    Thanks again and best regards
    Mario