Overload Protection

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I'm working on an embeeded system project that utilizes an Altera 7064 PLD (I know it's outdated but I'm a student) My question is general to any embedded device/processor.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

Reply to
Seth
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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

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Ian Bell
Reply to
Ian Bell

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

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Ing.Buero R.Tschaggelar - http://www.ibrtses.com
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Reply to
Rene Tschaggelar

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.

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Peter

Reply to
Peter

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

The > Hello,

Reply to
w_tom

I think what he means is latchup.

Reply to
Jim Stewart

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

Also take a look at 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.

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Paul E. Bennett ....................
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Reply to
Paul E. Bennett

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.

Reply to
David

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