Thanks Spehro!! That's absolutely excellent info!

From the results of your test on the PIC clamp diodes
they look VERY fragile. I consider the in4148 to be
too fragile, from the amount of them i've found faulty
in TVs and VCRs even in low voltage low current circuits.

But the PIC clamp diodes are poitively tiny based on
your V/I performance chart... I'll stick with my RCZ
networks on PIC inputs I think. :o)
-Roman

PS. Based on their max 20mA spec, and your measured
0.887v, Microchip seem to be speccing the clamp diodes
at max of 18mW... Death to the infidels. ;o)


Spehro Pefhany wrote:
>
> At 02:28 PM 8/6/01 -0400, you wrote:
> >I would like to see a careful measurement of it in the regions of interest
> >(below Vss and above Vdd):
>
> Ok, Bob:-
>
> -I did some measurements above Vdd on a single piece of 12C509JW
> -Programmed it to run on all internal and to just sit there with all inputs.
> -Connected all pins but power and GP0 to Vss through a 500 ohm resistor.
> -Vdd 5.00V
>
> - applied voltage above Vdd through a 100R 1% resistor.
>
> Current       Voltage
> (mA)          (V, relative to Vdd)
> 0.020         0.570
> 0.050         0.601
> 0.100         0.625
> 0.200         0.649
> 0.500         0.677
> 1.00          0.699
> 2.00          0.723
> 5.00          0.762
> 10.0          0.807
> 20.0          0.887
>
> I've attached a gif graph of the results.
> A typical 1N4148 diode data sheet is at:
> http://www.fairchildsemi.com/ds/1N/1N4148.pdf
>
> - At higher currents, the ratio of currents between the data sheet 1N4148
>   and the PIC is about 3:1.
>
> This doesn't seem to change the conclusions that either a series resistor or
> a Schottky diode is required in order to be very effective- a 1N4148 with no
> resistor should improve the minimum current that would cause latch-up by only
> about a factor of 3:1. A small resistor (even 100R) in series with the diode
> would improve this MUCH more (more than 500mA in this case).
>
> Best regards,
>
>     ---------------------------------------------------------------
>
>                               Name: inputchr.gif
>                Part 1.2       Type: GIF Image (image/gif)
>                           Encoding: base64
>
>     ---------------------------------------------------------------
>
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Spehro Pefhany --"it's the network..."            "The Journey is the reward"
> speff@interlog.com             Info for manufacturers: http://www.trexon.com
> Embedded software/hardware/analog  Info for designers:  http://www.speff.com
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