Pages: 1 [2]   Go Down
Author Topic: protection for digital input pin  (Read 1153 times)
0 Members and 1 Guest are viewing this topic.
Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 118
Posts: 4549
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
So you don't need any more.
Yes you do. 1mA is the maximum current that should flow through the internal protection diodes.

I actually said:

So you don't need any more.

(Assuming you've limited the number of amps that can reach the pin, eg. though a 10k resistor)

Logged

No, I don't answer questions sent in private messages...

Manchester (England England)
Online Online
Brattain Member
*****
Karma: 508
Posts: 31423
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
(Assuming you've limited the number of amps that can reach the pin, eg. though a 10k resistor)
The thing is that once you start putting 10K series resistors on inputs your noise immunity is shot and it limits the rise time of the signals. That is why I have a 22R series resistor so the protection circuit does not end up crippling the signal.
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 16
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

It's my page so yes I think it is good especially if you are only protecting against transients. If the voltage is going to be constantly over 5V then make that resistor something like 100R.

Got it smiley

I don't have a 100pF can I use other values?

What impact the capacitor values have?
Logged

Manchester (England England)
Online Online
Brattain Member
*****
Karma: 508
Posts: 31423
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
I don't have a 100pF can I use other values?
Yes, using other values will control the balance between protection against spikes and disrupting the input signal.
The capacitor absorbs voltage spikes ( good ) and also slows down the input rise time ( bad ) .
Logged

Pages: 1 [2]   Go Up
Jump to: