[PIC] Mid range PIC A-D query

[David C Brown]

Spec A25 for the PIC16F87X gives the range for an analog input to be
(Vss-0.3) < Vin < (Vref+0.3).

This is not listed as an Absolute Max Rating so I am wondering what the
consequences of exceeding the upper limit would be?

Would it damage the ship and, if so, is there a cunning way of protecting
it?


__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak Phone: [phone]
Derbyshire eMail: ***@gmail.com
SK23 7ND web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



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[Jason White]

Pure speculation follows:

If the input current is limited by a resistor, to say >100uA, it stands a
good chance of survival. Accuracy will go to heck on all channels due to
leakage of the offending signal into the IC.

-Jason White

Post by David C Brown
Spec A25 for the PIC16F87X gives the range for an analog input to be
(Vss-0.3) < Vin < (Vref+0.3).
This is not listed as an Absolute Max Rating so I am wondering what the
consequences of exceeding the upper limit would be?
Would it damage the ship and, if so, is there a cunning way of protecting
it?
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak Phone: [phone]
SK23 7ND web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>
*Sent from my etch-a-sketch*
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[Paul Hutchinson]

It depends on how much you exceed the limit. VCC +0.5 is unlikely to damage the chip although it may crash the chip. VCC +100.0 is virtually guaranteed to let out the magic smoke. :-)

To prevent problems add clamping diodes.

Paul Hutch

--------------------------------------------
On Sun, 8/27/17, David C Brown <***@gmail.com> wrote:

Subject: [PIC] Mid range PIC A-D query
To: "Microcontroller discussion list - Public." <***@mit.edu>
Date: Sunday, August 27, 2017, 11:52 AM

Spec A25 for the PIC16F87X gives the range
for an analog input to be
(Vss-0.3) < Vin  <
(Vref+0.3).

This is not listed as an Absolute Max
Rating so I am wondering what the
consequences of exceeding the upper
limit would be?

Would it damage the ship and, if so, is
there a cunning way of protecting
it?


__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak       
               
  Phone: [phone]
Derbyshire       
        eMail: ***@gmail.com
SK23 7ND       
  web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



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[Neil]

I current-limit with an inline resistor, and also voltage divide prior
to that. For say a 0-5V signal on a 5V-powered chip, using either a pair
of equal value resistors for the voltage divider I can get full ADC
scale with either (a) another pair of equal value resistors for the
Vref+ if it's ratiometric or (b) using a 2.5V reference (if it's absolute).

Cheers,
-Neil

Post by David C Brown
Spec A25 for the PIC16F87X gives the range for an analog input to be
(Vss-0.3) < Vin < (Vref+0.3).
This is not listed as an Absolute Max Rating so I am wondering what the
consequences of exceeding the upper limit would be?
Would it damage the ship and, if so, is there a cunning way of protecting
it?
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak Phone: [phone]
SK23 7ND web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>
*Sent from my etch-a-sketch*
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