• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 18 subscribers
  • Views 326 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.

PAL16L8A-2M: PAL16L8A-2M pin not used

Stefano Scremin
Intellectual 440 points
Part Number: PAL16L8A-2M

Dear All,

I need an information about PAL16L8A-2M.

I'm not an expert in programmable logic array and I have the following question: If I have some input and output "not used", what is the better configuration for these pins in schematic (pull-up to Vcc, pull-down to GND or "not-connected")?

Thank you in advance for your reply.

Stefano

  • 0
    TI__Guru 62930 points
    Stefano,
    It is appropriate to bias any unused inputs to a valid logic level. This can be VCC or GND depending on what is more convenient for your board/application.
    If you have an unused output (configured as an output), then it can be left floating.
    If it can be tristated or an input, then it would be best to treat it with weak pull up or down to insure it never floats.

    If this answers your question, please click "Verify it as the answer"
    Regards,
    Wade
  • 0 in reply to Wade Vonbergen
    Intellectual 440 points
    Dear Wade,
    thank you very much for your reply.
    Just another question: in pull-down case, is it recommended a low value resistor (ex. 100R) between pin and GND or 0R?
    Thanks in advance.
    Stefano
  • 0 in reply to Stefano Scremin
    TI__Guru 62930 points
    From a functional standpoint either will work. In fact it could be tied directly to GND or VCC.
    However, from a robust design standpoint, it would be good to include a resistor to protect against mistakes. This could include probing or if a device on same net shorts to VCC or GND, then the current would be limited. It also allows more ability to modify design after fabrication as the resistors pads can be used for blue-wiring.
    As far as picking best value for pullup or down. You need to consider the worst case leakage along with some margin.
    The device has input leakages listed worst case for VCC= 5.5 and Vi =5.5V of 200uA.
    At this low of leakage, I would consider using 10X the current. So, choose a pullup or down of 2ma across 5.5V. This is 2.75K. This could be safely rounded up or down to next common resistor sizes of 2.7K or 3.3K.

    If this answers your question, please click "Verify it as the answer"
    Regards,
    Wade
  • 0 in reply to Wade Vonbergen
    Intellectual 440 points
    It's clear.
    Thank you very much.
    Regards

    Stefano