Overload Protection

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Hello,
I have a question on embedded systems hardware.  Hopefully someone can
help.

I'm working on an embeeded system project that utilizes an Altera 7064
PLD (I know it's outdated but I'm a student)  My question is general
to any embedded device/processor.  I want to make my system as robust
as possible, and prevent the PLD from overloading.  A friend of mine
suggested adding a resistor between Vdd and the PLD that would drop
the voltage below the chip's minimum operating level if the current
was too large.  For my operation frequency (16 MHz) the PLD is rated
at a typical supply current of 30mA from a 5V source.  I calculated
that a 10 Ohm resistor would only drop the voltage  by .3V under
normal usage but would drop a full 1V if 100mA were drawn, shutting
off the device.  However, this resistance seems very small to me.
Perhaps because I am using an older device with a large current draw.

Can anyone tell me if this is a good method to prevent an embedded
device from overloading or suggest a better alternative?

Thanks!!
-Seth

Re: Overload Protection

Quoted text here. Click to load it

No this is not a good method for several reasons. Also you do not say what
you really mean by overloaded except that it results in the processor
drawing more current. if this current is due to a fault in the processor
then the method below will do the job.

Try a 100mA anti-surge fuse.

Ian


--
Ian Bell

Re: Overload Protection

Quoted text here. Click to load it

The typical supply current applies for 10% of the gates
in use. Just have a look at the fine print. A series
resistor is a suboptimal choice. I'd suggest a lab power
supply for the develoment. Just in case you have open inputs
(they can oscillate) or outputs shorted to GND, the chip
may overheat and destroy itself, unless you limit the current.
Afterwards, the chip will take what you measured it to draw.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

Re: Overload Protection

Quoted text here. Click to load it

A series resistor sounds like a dreadful idea because it will make your
supply rail prone to noise and brown outs. You need to design your circuit
so that it's not going to short circuit gates together.

With my personal projects I protect them by using a voltage regulator with
current limiting. The L200CV can be set to any voltage and by using a sense
resistor in the output you can limit the output current.

Here is a simple guide to power supplies that features the L200CV.
http://www.fraw.org.uk/pubs/sspji/sspji-03.pdf

Peter



Re: Overload Protection
  What are you overloading?  Output drivers? Power bus? Data
bus?  Power supply?  AC input power or battery?  CPU?

  The only overloading you are not asking about is overloading
of variables in software.

Seth wrote:
Quoted text here. Click to load it

Re: Overload Protection
Quoted text here. Click to load it

I think what he means is latchup.

Quoted text here. Click to load it

Re: Overload Protection

Quoted text here. Click to load it

Take this link to my articles "Reading the World" and "Writing the World".

 <http://www.amleth.demon.co.uk/library/articles/forth/fighard/Intro.htm

Also take a look at <http://www.ganssle.com/ where you will find a number
of useful articles. You should also find a link to Jacks book on embedded
systems which includes lots of useful guidance.

It takes more than just a well placed resistor to make the interfaces
really robust and able to live in the real world. Mostly it is energy
management.

--
********************************************************************
We've slightly trimmed the long signature. Click to see the full one.
Re: Overload Protection

Quoted text here. Click to load it

How about an automatic fuse?  On overload, they overheat and switch off,
protecting the circuit.  When cool they switch on again, so you don't have
to change them.  You only get a noticable voltage drop or other problems
if you are drawing close to the fuse's rating.


Site Timeline