From: "Spehro Pefhany"
Subject: Re: Resistor proetection for the PIC16F874
User-Agent: tin/pre-1.4-19990216 ("Styrofoam") (UNIX) (Linux/2.2.14 (i586))
Date: Sun, 08 Sep 2002 16:29:14 GMT
NNTP-Posting-Date: Sun, 08 Sep 2002 12:29:14 EDT
The renowned Danny wrote:
> I am using the PIC16F874 for a project, and I need to know how to connect
> the input current protection resistors, and also the output protection
> resistors. I mean like parallel or serial/series.
As in the snarky reply ;-), you can use George Simon Ohm's law to
determine series resistance that won't cause latchup. Limiting the current
to a few mA is typical (the latchup limit is much higher). The chip will
survive this, but correct operation in all respects is not guaranteed.
> And do you have a formula to calculate the resistance?
> any help would be very much so appreciated
However, you may wish to clamp the voltage inside the power supply
rails to prevent side effects of running current through the protection
diodes, particularly if you are using the 10-bit A/D in this part. You can
do this with 2 dual transistors and a resistor per input, which will clamp
the input to within about 100mV of the rails, well within the 300mV
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