GTBecker
Joined: 18 Jan 2006
Posts: 457
Location: Cape Coral
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Posted: 10 June 2010, 20:59 PM Post subject: Max pin current |
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An application calls for momentary ~+18v through 100k to a processor input pin. The classic protective solution calls for a clamp diode from the pin to Vcc, and clamp diodes are, I believe, already provided on the processor.
Assuming that and Vcc=5v, the pin would never exceed ~+5.4v; the clamp diode would draw current through the 100k if the voltage applied to the resistor exceeds that. So, for +18v, the current into the pin would be (18v-5.4v)/100k= ~126uA.
I believe that should be safe. Is it? |
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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 10 June 2010, 23:19 PM Post subject: Re: Max pin current |
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| GTBecker wrote: | | So, for +18v, the current into the pin would be (18-5.6)/100k= ~124uA. I believe that should be safe. Is it? |
My reading of the datasheet indicates that that current should be safe. There is no explicit specification like "maximum protection diode current" but there is "DC Current per I/O Pin ... 40.0mA" in the "Absolute Maximum Ratings" section.
The problem would be if the clamping diode fails open. That is why I've suggested using an external clamping diode. |
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