simulate this circuit – Schematic created using CircuitLab

This is a simplified example of a push pull GPIO found in most microprocessors, with a load attached.

Using the capacitance and current values from the datasheet that is usually given in a microprocessor datasheet, how can the rise time be calculated?

  • \$\begingroup\$ I noticed there was not a good question about calculating rise times, so I created one. I'll answer it if no one else does. \$\endgroup\$ – Voltage Spike Oct 9 '19 at 16:56
  • \$\begingroup\$ What do R1 and C1 represent? \$\endgroup\$ – Huisman Oct 9 '19 at 16:57
  • \$\begingroup\$ GPIO capacitance, and line resistance (which is most of the time negligible) \$\endgroup\$ – Voltage Spike Oct 9 '19 at 17:01
  • 2
    \$\begingroup\$ Nice idea but, to make it worthwhile for that, you need to fill the question out a lot more before thinking about the answer. Guide new posters through what a decent question should look like. \$\endgroup\$ – TonyM Oct 9 '19 at 17:01
  • 3
    \$\begingroup\$ What is the output transition rate for a logic device? \$\endgroup\$ – CL. Oct 9 '19 at 18:42

For this, and if you have access to it, you should better use IBIS models for the I/O cell.

The IBIS model not only provide for rise time and fall time modelling but also includes ESD diodes modelling which will make your simulations much more accurate (see Fig 9. for diagram).

  • \$\begingroup\$ Thanks but I'm looking for more of a hand calculation, IBIS models require expensive software. \$\endgroup\$ – Voltage Spike Nov 5 '19 at 22:40
  • \$\begingroup\$ Unfortunately, this sort of data usually isn't available for hand calculations. Something like a IBIS -> SPICE converter might help, but still wouldn't give you hand calculations. \$\endgroup\$ – user2943160 Nov 29 '19 at 21:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.