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AnsweredHot!PIC24EP: Need information on internal protection diodes

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sushant_shidore
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2019/12/08 22:27:29 (permalink)
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PIC24EP: Need information on internal protection diodes

I've gone through datasheet and reference manuals meant for PIC24EP128GP206, and came across a statement -
"Certain pins have internal protection diodes to VDD and VSS".
 
I'm looking for getting more information on these diodes, their capacity to clamp voltages, their specifications, internal connection diagram etc. but cannot find it anywhere.
Can someone please guide me to find it?
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ric
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Re: PIC24EP: Need information on internal protection diodes 2019/12/09 21:02:05 (permalink) ☄ Helpfulby sushant_shidore 2019/12/10 20:33:24
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Have a look in the datasheet under "ABSOLUTE MAXIMUM RATINGS"
ww1.microchip.com/downloads/en/DeviceDoc/70000657H.pdf#page=401
 
The "Voltage on any pin that is not 5V tolerant, with respect to VSS(3).................................................... -0.3V to (VDD + 0.3V)"
spec is telling you the forward voltage of those diodes.
On those pins, there is one connected from VSS to the pin (anode to VSS), and from pin to VDD (cathode to VDD)
so they are obviously shottky diodes with a forward voltage of 0.3V.
I don't know if this datasheet mentions it, but they are usually only rated for 20mA current.

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NKurzman
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Re: PIC24EP: Need information on internal protection diodes 2019/12/09 21:57:23 (permalink)
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What are you planning to do with the diodes?
Note that abusing them can create problems.
Like overvoltaging analog pins can affect the ADC accuracy on other pins.
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ric
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Re: PIC24EP: Need information on internal protection diodes 2019/12/09 22:02:11 (permalink)
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+1
In short, it is NEVER a good idea to allow any of these diodes to conduct.
Microchip did have some app notes that depended upon it years ago. To the best of my knowledge, they have all been removed from the website.
If you need clamping, add your own external components to do it. They are much easier to replace than the whole PIC, and sure to be able to handle more current.
 

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MBedder
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Re: PIC24EP: Need information on internal protection diodes 2019/12/10 01:15:12 (permalink) ☼ Best Answerby sushant_shidore 2019/12/10 20:49:09
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Shottky diodes are never implemented in CMOS ICs because it's an almost incompatible technological process.
 
+-0.3V over supply rails is stated to indicate the maximum voltage which is guaranteed to not open these diodes.
 
The maximum clamp current through these diodes is stated in the datasheet referred to as "Injection Current" which is +-5 mA.
 
The internal connection diagram is fairly simple - every pin has its normally closed "lower" diode (to VSS), every non-5V tolerant pin also has its normally closed "upper" diode (to VDD), and every 5V tolerant pin has its normally closed "upper" diode to an internal 5V zener's anode (the cathode of that zener is connected to VSS).
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sushant_shidore
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Re: PIC24EP: Need information on internal protection diodes 2019/12/10 20:30:08 (permalink)
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NKurzman
What are you planning to do with the diodes?
Note that abusing them can create problems.
Like overvoltaging analog pins can affect the ADC accuracy on other pins.



I'm not going to abuse or overload the diodes in any way.
I'm just documenting for the purpose of knowing limits of I/O ports used in my application.
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ric
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Re: PIC24EP: Need information on internal protection diodes 2019/12/10 22:03:52 (permalink)
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sushant_shidore
I'm just documenting for the purpose of knowing limits of I/O ports used in my application.

For any semiconductor device, you look in the "ABSOLUTE MAXIMUM RATINGS" paragraph for that information.
 

I also post at: PicForum
Links to useful PIC information: http://picforum.ric323.co...opic.php?f=59&t=15
NEW USERS: Posting images, links and code - workaround for restrictions.
To get a useful answer, always state which PIC you are using!
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