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F2810 PORT D and A sink current

Gustavo
Prodigy 120 points


Hi.

I'm using some F2810 pins as digital inputs.

Port B and G pins are sinking 2uA as described in datasheet.

But pins from ports A and D must be sinking 65uA for the voltage I have in the input.

 

Has anyone seen something like that?

 

 

  • 0
    TI__Expert 8500 points

    Gustavo,

    Do you by chance mean the pins are sourcing the current? Most of the pins have internal pullup circuits. Could this be the culprit? Port G pins do not have a pullup and the pullups on Port B are weaker than on the other pins.

    Regards,
    Dave Foley

     

  • 0 in reply to David Foley
    Prodigy 120 points

    Hi David!

     

    I read relay contacts, open ou closed.

    So, 5V outputs through R54 (10k) and goes to contact (ENT_DIG00_A). It returns through R60 (10k) (ENT_DIG00_B), making a voltage divisor with R57 (39k), going to processor's input pin (IN_DIG00_PIN).

    D62 and D61 are 1N4148 diodes or similar.

     

    Contact open, IN_DIG00_PIN = 0V. Contact closed, IN_DIG00_PIN = 5V* [39k / (39k+10k+10k)] = 3.3V.

     

    So, the following pins are working nice: Port B pins 11 to 15; Port G pins 4 and 5;

    When open, they have approximately 0.8V, which matches to 39k * 2uA (input low current). Ok!

    And when closed, 3.3V.

     

    But following pins are always having 2V when contact is open: Port D pins 1, 5 and 6; Port A pins 11 to 15.

    As there is the coincidence between port pins behavior, I believe there must be something related to the PORT (D and A). Could they have a input low current bigger than 2uA?

    Regards,

    Gustavo.

     

  • 0 in reply to Gustavo
    TI__Expert 8500 points

    Gustavo,

    The 2uA spec is for pins without pullups/pulldowns or when the pin is biased in the same direction as the pull. Most of the pins have pullups, which will try to pull the voltage on the pin up when you try to ground it via a resistor. A handful of pins have pulldowns, including Port G. Port B has weaker pullups then the rest of the pins. 39k * 2uA = 0.078v, not 0.8v. A max of 0.078v is what I would expect to see on Port G. The 0.8v that you are seeing corresponds to 20.5uA, which is in the IIL range of Port B specified in the datasheet. I suspect you are seeing 0.8v for Port B only and may have been confused on your Port G measurements. The 2v you are seeing on the other pins corresponds to 51uA, which is actually a little low for the IIL range of the Port A and D pins. I would have actually expected to have seen higher than 2v. You need stronger external pull down resistors to overdrive the internal pullups on these pins. I would suggest around 2k. I would suggest a stronger pulldown on the Port B pins as well as 20.5uA is on the low side of the range so you could see a higher voltage than 0.8v on another batch of devices or across temperature and supply voltage.

    Regards,
    Dave Foley

     

  • 0 in reply to David Foley
    Prodigy 120 points

    Hi Dave!

    Is there some way to disable the pull-up resistors?

    I understood your explanation about changing external pull-down resistors, but I don't intend to change 10k resistors. Probably the best to have high input impedance and match pull-down requirements for ports A and D could be use a driver like HC245?

    Port G is working like port B, but anyway, as far as I can see, I'm not in safe way...

     

    Thank you very much for your answer and support.

     

    My best regards,

    Gustavo.

     

  • 0 in reply to Gustavo
    TI__Expert 8500 points

    Gustavo,

    Unfortunately on the F281x product line there is no way to disable the pullups. On later products we have given that option, but not on the F281x devices. Sorry.

    Regards,
    Dave Foley