Timeline for Is there a GPIO current limit function available, and where is the documentation?
Current License: CC BY-SA 4.0
11 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jul 22, 2020 at 22:17 | vote | accept | Seamus | ||
| Apr 1, 2019 at 15:00 | history | tweeted | twitter.com/StackRaspi/status/1112731470748139520 | ||
| Apr 1, 2019 at 12:09 | comment | added | Seamus | @joan: Thanks for the clarification. I never imagined the output would operate as a current source (tho' that would have its uses :) , and I get your point about the scribd doc being nuanced. I do want to have an unequivocally correct answer to my question though... you got time for a Chat session today? | |
| Apr 1, 2019 at 11:55 | comment | added | joan | "... If it succeeds depends on what is connected. If the pad is shorted to ground it will not be able to drive high. In fact it will try to deliver as much current as it can and the current is only limited to what the internal resistance is. If you drive the pad high and it is shorted to ground in due time it will blow up!The same holds true if you connect it to 3V3 and drive it low." | |
| Apr 1, 2019 at 11:55 | comment | added | joan | No, I am trying to summarise the scribd document. "What does the current value mean? The current value specifies the maximum current under which the pad will still meet the specification. It is not: The current that the pad will deliver. It is not: A current limit so the pad will not blow up.The pad output is a voltage source. If set high the pad will try to drive the output to the rail voltagewhich on the Raspberry-Pi is 3V3 (3.3 Volts). If set low the pad will try to drive the output to ground (0 Volts). As the text says: the pad will try to drive the output high or low..." | |
| Apr 1, 2019 at 11:35 | comment | added | Seamus |
@joan: If I understand what you're saying, it's this: While you can set current limits on the GPIO in software, those limits are, for all intents and purposes, meaningless. For example, you can set the current limit to 2mA, yet if you connect a load of 330 Ohms from that pin to ground, and set the pin to "HIGH" (3.3V)) the pin will source 10 mA, not 2 mA.
|
|
| Apr 1, 2019 at 7:20 | comment | added | joan | Not quite. I am pointing out that these are not current limits. The default pad setting is 8mA. You can still draw say 16mA from that GPIO. However the hardware no longer promises that the voltage will still be high enough to be seen as a logic 1 on that GPIO. For instance it might have dropped to 2V7. | |
| Mar 31, 2019 at 20:13 | comment | added | Seamus | If you're suggesting that the scribd document may have details that aren't in the Foundation's "official" documentation, I agree with you. This Q&A has been in my "to do list" for nearly 9 months. My original intent was to verify the scribd document, but I wasn't quite able to do that. What I did get from the maintainers was an update to the "official documentation" that addressed the GPIO current limit. I figured that was worth "publishing" here in hope that some would benefit. But if you have thoughts or suggestions, I'll happily try to incorporate those. | |
| Mar 31, 2019 at 19:56 | comment | added | joan | The title may mislead. The scribd document is quite nuanced and is all about how much current may be sourced/sinked from a GPIO while still maintaining the correct (driven) logic level. | |
| S Mar 31, 2019 at 19:36 | answer | added | Seamus | timeline score: 6 | |
| S Mar 31, 2019 at 19:36 | history | asked | Seamus | CC BY-SA 4.0 |