Searching \ for ' [PIC] kill a PIC' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/microchip/devices.htm?key=pic
Search entire site for: 'kill a PIC'.

No exact or substring matches. trying for part
PICList Thread
'[PICLIST] [PIC] kill a PIC'
2002\02\24@110318 by Graeme Zimmer

flavicon
face
Chis,

> The best way to unexpectedly kill a PIC through I/O that I have seen,
> although I have not been stupid enough to try it myself - is to attempt to
> implement the MC ap note on triac control, where it suggests (and shows a
> drawing of) connecting the AC line directly to I/O for zero-cross
> detection - relying on the pin's internal protection diodes.

> That was just a ridculous idea to try and implement.

I can see no problem with this, as long as the series resistor
is large enough to limit the maximum current to the manufactures
specification.


.......................... Zim

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email spam_OUTlistservTakeThisOuTspammitvma.mit.edu with SET PICList DIGEST in the body


2002\02\24@113022 by michael brown

flavicon
face
> Chis,
>
> > The best way to unexpectedly kill a PIC through I/O that I have seen,
> > although I have not been stupid enough to try it myself - is to attempt
to
{Quote hidden}

This is what I like to refer to as TV set engineering.  ;-D  (ducking for
cover now)  IMHO, TV set design and antenna theory (vs. reality) are
indistinguishable from black magic.  I tend to eventually "let the smoke
out" of TV's when I try to tinker with them.  So now I stick with moderately
low-voltage (120V or less) equipment with somewhat understandable
schematics.  You know.....not like TV's.  ;-)  I respect the ability of
people to connect high-voltage directly to pic by not exceeding the current
limits, but it still seems a little risky to me.  I tend to expect that
touching a pin on an IC is not going to shock me.  That hot chassis stuff
'gets' me every time.  ;-D

michael

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email .....listservKILLspamspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body


2002\02\24@192935 by 859-1?Q?Alexandre_Guimar=E3es?=

flavicon
face
Hi,

> > The best way to unexpectedly kill a PIC through I/O that I have seen,
> > although I have not been stupid enough to try it myself - is to attempt
to
{Quote hidden}

   It is almost impossible to keep it under the maximum current allowed all
the time !!! Remember that you have many high voltage spikes going on any
regular power line. Even more if you are using a dimmer that generates lots
of noise. Imagine that switching a heavy inductive load such as a halogen
lamp transformer ! The internal diodes cannot protect from these spikes. You
have to use external protection to make sure you do not violate the specs.
That application note has always amased me because it is just pure bad
enginnering. I would never use that to make a real product.

Best regards,
Alexandre Guimaraes

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspamKILLspammitvma.mit.edu with SET PICList DIGEST in the body


2002\02\24@220540 by Spehro Pefhany

picon face
At 12:12 PM 2/24/02 +1100, you wrote:

>I can see no problem with this, as long as the series resistor
>is large enough to limit the maximum current to the manufactures
>specification.

I don't see any *inherent* problem with it, but trying it with a
standard 0.25W resistor is practically guaranteeing trouble, and
I doubt it would pass safety certification in any developed
country.

Instead use an approved resistor rated for a few thousand volts,
which might cost 10-20 cents rather than << 1 cent. Philips'
VR37 series meets the requirements, and can be bent to fit 0.5"
pitch pads.

The value should be high enough that enough current to cause
latchup will not flow *even under transient conditions*.

Best regards,







>.......................... Zim
>
>--
>http://www.piclist.com#nomail Going offline? Don't AutoReply us!
>email .....listservKILLspamspam.....mitvma.mit.edu with SET PICList DIGEST in the body

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspam_OUTspamTakeThisOuTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspamspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body


2002\02\25@001231 by George Tyler1

flavicon
face
I know this should be OK in theory as it is in the manufacturer's specs, but
in practice I would never design a curcuit for mass production like that, or
do anythink that could take any pin outside the supply voltage range, even
using schottkey diodes to clamp the pins could be dangerous. There is a
parasitic scr in every chip waiting to be fired!

{Original Message removed}

2002\02\25@083414 by Spehro Pefhany

picon face
At 07:00 AM 2/25/02 +0200, you wrote:
>I know this should be OK in theory as it is in the manufacturer's specs, but
>in practice I would never design a curcuit for mass production like that, or
>do anythink that could take any pin outside the supply voltage range, even
>using schottkey diodes to clamp the pins could be dangerous. There is a
>parasitic scr in every chip waiting to be fired!

Junction-isolated CMOS chips (which is most of them), yes. If you guarantee
the current will never get to the trigger current (which is tested) then
you'll be safe on that account. That's why you need a resistor that won't
arc over for even an instant, with say 3-4,000 volts applied. Remember that
similar voltages are created by walking across a carpet, so pins that are
brought out need similar protection.

P.S. I agree with distrusting application notes. I have been burned in the
distant past by using application note circuits (from RCA), bought samples
and wasted several days before I realized that the app note circuit could
*never* work reliably. Now I always do the calculations from the min/max
figures on the data sheet, and don't trust the people who wrote the app
notes (who seem to be young and inexperienced engineers trying to be
clever and sell chips, and don't put the care in there to make a commercial
conservative design that will always work under a wide set of conditions).

In a way, it's a bit like suckering you in.. here buy our part and you can
make this product with only 17 parts. If they showed you the 34 you really
need to do a good job, you'd shrug and flip the page. Unfortunately, some
are suckered to the point of actually trying to produce the "design" with
the 17 parts and get burned. I've just been struggling with such a
PIC "design" that someone else did. 8-(

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
@spam@speffKILLspamspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

--
http://www.piclist.com hint: To leave the PICList
KILLspampiclist-unsubscribe-requestKILLspamspammitvma.mit.edu


2002\02\25@094734 by Graeme Zimmer
flavicon
face
> The internal diodes cannot protect from these spikes.
> ......
> That application note has always amased me because it is just pure bad
> enginnering.

Let's see, the PIC input diodes can take about 20mA (I'm guessing).

With a 100K resistor, that's 2KV input
With 1Meg  that's 20 KV .

And BTW, that's continuous current.
For narrow pulses, the PIC could handle proportionally more current.

My point is that the resistor will die long before the PIC !
(a 1 Meg resistor with 20 KV across it is dissipating 400 Watts !!)

And of course you would have a small cap at the PIC to filter out the HF
junk.
This cap would  also greatly limit any spikes.

The weakest link would be the voltage rating of the resistor, you would need
a couple in series at least.
And yes, I personally would put a MOV or something at the junction of the
resistors.

Just pointing out that the App note isn't crazy when you actually do the
sums...

..................... Zim

--
http://www.piclist.com hint: To leave the PICList
RemoveMEpiclist-unsubscribe-requestTakeThisOuTspammitvma.mit.edu


2002\02\25@100058 by Spehro Pefhany

picon face
At 01:50 AM 2/26/02 +1100, you wrote:

>And BTW, that's continuous current.

Absolute maximum clamp current is +/-20mA. Absolute maximum.

>For narrow pulses, the PIC could handle proportionally more current.

Unh, no, not a good assumption.

>My point is that the resistor will die long before the PIC !
>(a 1 Meg resistor with 20 KV across it is dissipating 400 Watts !!)

More likely it is arcing and dissipating 40kW ;-)

>And of course you would have a small cap at the PIC to filter out the HF
>junk.
>This cap would  also greatly limit any spikes.

Really? Without doing the math, I'd certainly think that any such
capacitor would cause a lot of phase shift before it did much good.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spamBeGonespeffspamBeGonespaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

--
http://www.piclist.com hint: To leave the PICList
TakeThisOuTpiclist-unsubscribe-requestEraseMEspamspam_OUTmitvma.mit.edu


2002\02\25@101725 by Michael Rigby-Jones

flavicon
face
{Quote hidden}

This topic has been discussed numerous times on the list.  IIRC, the general
feeling was that injecting currents into the protection diodes caused
unpredictable behaviour and was best avoided.  The magnitude of current was
well below that which could cause any kind of SCR latchup as well.

I'll have a scan through the archives if I get 5 minutes.

Mike

--
http://www.piclist.com hint: To leave the PICList
EraseMEpiclist-unsubscribe-requestspammitvma.mit.edu


2002\02\25@104958 by 859-1?Q?Alexandre_Guimar=E3es?=

flavicon
face
> > The internal diodes cannot protect from these spikes.
> > ......
> > That application note has always amased me because it is just pure bad
> > enginnering.
>
> Let's see, the PIC input diodes can take about 20mA (I'm guessing).

   20 ma is the correct number.

> With a 100K resistor, that's 2KV input
> With 1Meg  that's 20 KV .
>
> And BTW, that's continuous current.
> For narrow pulses, the PIC could handle proportionally more current.

   Not at all. That is instantaneous. The latch-up will occur very fast as
the semi conductor areas are very small. It is not triggered by temperature
rise, as fas as I know.

> My point is that the resistor will die long before the PIC !
> (a 1 Meg resistor with 20 KV across it is dissipating 400 Watts !!)

   The chip will enter scr latch up before the resistor even fells the
problem. The spikes will arc over the resistor and even if they dont they
will not harm the resistor because they are very fast.

> And of course you would have a small cap at the PIC to filter out the HF
> junk.
> This cap would  also greatly limit any spikes.

   The cap will not help much. It will not act fast enough !

> The weakest link would be the voltage rating of the resistor, you would
need
> a couple in series at least.
> And yes, I personally would put a MOV or something at the junction of the
> resistors.

   The MOV, a very fast one, would make the design more reliable. I would
use 2 resistors in series and the MOV in the junction of the resistors. That
should be enough to keep the high voltage out.

> Just pointing out that the App note isn't crazy when you actually do the
> sums...

   Sorry but I would never use that without the MOV's at a product of mine.

Best regards,
Alexandre Guimaraes

--
http://www.piclist.com hint: To leave the PICList
RemoveMEpiclist-unsubscribe-requestEraseMEspamEraseMEmitvma.mit.edu


2002\02\25@131324 by George Tyler1

flavicon
face
I had a curcuit just like this, getting z-crossing pulses from mains,
clamped by a zener at one stage, an external clamp diode  before that. I
make about 500 samples of the product to test and experienced occasional
unexplained failures. I then added a small bipolar transistor before the
pic, and that solved the problem. One thing to watch out for.... on power
up, when the supply to the pic is low, a zener clamp is still above the
supply!
Regards,
   George Tyler
{Original Message removed}

2002\02\25@163208 by Dwayne Reid

flavicon
face
At 09:22 PM 2/24/02 -0300, Alexandre Guimarães wrote:

>     It is almost impossible to keep it under the maximum current allowed all
>the time !!! Remember that you have many high voltage spikes going on any
>regular power line. Even more if you are using a dimmer that generates lots
>of noise. Imagine that switching a heavy inductive load such as a halogen
>lamp transformer ! The internal diodes cannot protect from these spikes. You
>have to use external protection to make sure you do not violate the specs.
>That application note has always amased me because it is just pure bad
>enginnering. I would never use that to make a real product.


At 03:15 PM 2/25/02 +0000, Michael Rigby-Jones wrote:

>This topic has been discussed numerous times on the list.  IIRC, the general
>feeling was that injecting currents into the protection diodes caused
>unpredictable behaviour and was best avoided.  The magnitude of current was
>well below that which could cause any kind of SCR latchup as well.

I can comment on both the above statements:

I *do* use a PIC input pin to sample zero-cross in several products.  There are 2 - 1 Meg resistors (0.25W, 400V) in series to sample a 120 Vac input.  Some boards have 1n4148 clamps to Vdd & Gnd, some boards have a 4.7V zener clamp to Gnd, some boards have no external diode clamps.  I don't use a capacitor filter at the pin if the intent is to sample zero crossing (too much phase shift) but do use a capacitor if the requirement is only use the AC mains as a timebase.

I have had *NO* failures related to this out of several thousand boards - even those without external diode clamps.  But I did a couple of things ahead of time:  I qualified the resistors I use by testing several hundred pieces with a pulsed 1200 Vac supply to ensure that they do not break down or arc  *and*  I have a MOV at the front end of the board - where the 120 Vac enters the card.  I feel that 2 resistors in series, each resistor having a 10x test margin, is adequate.

I *always* use clamp diodes if the PIC has a/d input that I am using.  I have measured significant a/d errors on the 12c671, 16c71, 16c73 parts if there is *ANY* substrate current resulting from the ESD protect diodes conducting because some other input pin was above Vdd or below Gnd.  I don't know about the comparitor inputs on the '62x family of parts - I'll find out when I do a project that actually uses those those features.

On the other hand, minor substrate currents (0.1 mA or less) appear to have no effect on the purely digital inputs on the PICs I have used to date.

Finally, this (2 resistors + MOV) seems to work for me with a 120 Vac mains supply.  All bets are off at higher voltages.

dwayne


Dwayne Reid   <RemoveMEdwaynerspam_OUTspamKILLspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 18 years of Engineering Innovation (1984 - 2002)
 .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-
    `-'   `-'   `-'   `-'   `-'   `-'   `-'   `-'   `-'
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.

--
http://www.piclist.com hint: To leave the PICList
RemoveMEpiclist-unsubscribe-requestTakeThisOuTspamspammitvma.mit.edu


2002\02\26@005133 by 859-1?Q?Alexandre_Guimar=E3es?=

flavicon
face
Hi, Dwayne

> I *do* use a PIC input pin to sample zero-cross in several products.
There
> are 2 - 1 Meg resistors (0.25W, 400V) in series to sample a 120 Vac
> input.  Some boards have 1n4148 clamps to Vdd & Gnd, some boards have a
> 4.7V zener clamp to Gnd, some boards have no external diode clamps.  I
> don't use a capacitor filter at the pin if the intent is to sample zero
> crossing (too much phase shift) but do use a capacitor if the requirement
> is only use the AC mains as a timebase.

   It is ok to have the pin connected that way, you are protecting it.

> Finally, this (2 resistors + MOV) seems to work for me with a 120 Vac
mains
> supply.  All bets are off at higher voltages.

   The MOV is giving you the reliability you need ! You can be pretty sure
that 120 Vac is not 2Kvolts. I do not like diode clamps to VCC or GND at
all. You inject all the noise into your power supply and may get many
components in trouble. Small voltage surge arrestors are available and are
not too expensive. That way you just dissipate the spikes as heat and do not
propagate them trough all the board at the power supply rails.

Best regards,
Alexandre Guimaraes

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


More... (looser matching)
- Last day of these posts
- In 2002 , 2003 only
- Today
- New search...