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GPIO Current

Sergio4668
Prodigy 170 points
Other Parts Discussed in Thread: TMS320F28335

Hi Folks,

The TMS320F28335 Data Manual says the  GPIO's output current can be +/-8mA. Does anybody know if there is a maximum number of pins which can be sourcing 8mA at the same time?

Hope you'll help me.

Regards

Sergio

  • 0
    TI__Expert 4745 points

     

    Yes, there is a limitation...not all of the GPIOs have this capability...only the ones that are muxed in with the XINTF pins.

    See page 24 in SPRS439F.

    "All pins capable of producing an XINTF output function have a drive strength of 8 mA (typical). This is true even if the pin is not configured

    for XINTF functionality. All other pins have a drive strength of 4-mA drive typical (unless otherwise

    indicated)."

  • 0 in reply to DaveB123
    Prodigy 170 points

    MIng,

    What you pointed out is correct. However, maybe I haven't been clear on my question. If I configurate the muxed in with XINTF pins as GPIO pins, is it possible to source 8mA per pin at the same time? That is, if there are 52 XINTF pins configurated  as output, can the DSP source 52*8mA= 416mA, at the same time? This is the limit I am talking about.

    I hope I have made it more clear this time

    Sergio

  • 0 in reply to Sergio4668
    TI__Expert 4745 points

    Sergio,

    Yes it's clearer but not totally clear yet... : )

    I would really like to understand what you have in mind...the reason for the more robust spec on these GPIO/XINTF pins for current drive is not so much about their ability to drive current as it is that they are spec'd to switch more cleanly and quickly. 

    Are you planning on switching all the pins on and off simultaneously at the full speed and drawing 8mA?  If so, your going to really stress the total system.  Address lines typically switch somewhat randomly or in a fairly linear progression.  The device is not typically thought of as having to support a 416 mA load switched on and off at the XINTF speed.

    What is your switching speed? And how many pins are switching simultaneously?

    Another apps engineer is researching the worst case scenario and will post here as well.

  • 0 in reply to DaveB123
    Prodigy 170 points

    Ming,

    The reason why I wanted to know the driving current is design. I wanted to know which the maximun limit was in order to scale my hardware design. All this issue is clear for me, now [:Y]. I really appreciate your help. Thank you very much.

    Regards,

    Sergio