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CC2538: Internal PU Resistor Value and Digital Transistor

Kenley
Intellectual 1805 points
Part Number: CC2538


Tool/software:

Hi team,

①Can you tell me the internal PU resistor value of max/min? On the datasheet, there is a description that the typ is 20k Ω, but there is no description of max/min, so we have contacted.

②During reset, the partial pressure value will be applied to the GPIO of CC2538 as described below. Is there any problem?

The CC2538 GIPO has circuits that drive several digital transistors (NPNs).
Many of the CC2538 GPIOs are internal PU during reset. (The CC2538 side is the input.)
If the digital transistor is not chosen well, there is a problem that the digital transistor will drive inadvertently during reset.
On the other hand, the voltage divided between the built-in PU resistor of the CC2538 and the built-in resistor of the digital transistor will be applied to the CC2538. 

Best regards,

Kenley

  • 0
    TI__Mastermind 21300 points

    Hi,

    The min-max range on this may vary widely according to the VDD applied.

    I will try to get some answers from validation team about test data.

    Regards

  • 0 in reply to FI
    TI__Intellectual 1805 points

    Hi FI,

    Thank you for your support.

    Looking forward to your feedback.

    Regards,

    Kenley

  • 0 in reply to Kenley
    TI__Intellectual 1805 points

    Hi Farrukh,

    How is the current situation right now ?

    Regards,

    Kenley

  • 0 in reply to Kenley
    TI__Genius 12960 points

    Hi Kenly,

    Sorry for the delay here. Note that this is an older part within our portfolio with limited support. From the information I could gather on the device there is a larger variation over conditions for the internal PU resistor. For such devices it can vary from 10K to 100K with 20K being the TYP. In this case, if you want a more precision PU its best to have this external so that you would have more control. 

    Thanks,

    Riz

  • 0 in reply to Rizwan Murji
    TI__Intellectual 1805 points

    Hi Rizwan

    Thank you for your support.

    How about this question ?

    ②During reset, the partial pressure value will be applied to the GPIO of CC2538 as described below. Is there any problem?

    The CC2538 GIPO has circuits that drive several digital transistors (NPNs).
    Many of the CC2538 GPIOs are internal PU during reset. (The CC2538 side is the input.)
    If the digital transistor is not chosen well, there is a problem that the digital transistor will drive inadvertently during reset.
    On the other hand, the voltage divided between the built-in PU resistor of the CC2538 and the built-in resistor of the digital transistor will be applied to the CC2538. 

    Regards,

    Kenley

  • 0 in reply to Kenley
    TI__Genius 12960 points

    Hi Kenley,

    If I understand the concern here it is that when the CC2538 device is reset you will have a voltage equivalent to the voltage divider of the PU resistor and the internal resistance of the NPN transistor. Thus when the device is in reset there will be a voltage applied to the GPIO of the C2538 device.

    IF this is the scenario, I also am assuming that there will still be a VDD applied to the CC2538 and then a reset is applied. There should be no issue in this scenerio as long as you ensure that the voltage on any digital pin is within the absolute max rating per the datasheet:

    In this case in needs to be below a max of 3.9V. So as long as the voltage divider with the PU and NPN transistor does not exceed this value there will be no issue.

    Thanks,

    Riz