SX28 Temp at 50mhz

Keith M

Is it normal for the SX28 running on the Tech board at 50mhz to be hot --- hot enough to burn your finger if you leave it on it?

This seems too hot for normal operation.· Will an extremely tight loop cause this problem?

I also noticed that the voltage regulator gets super hot as well.

I haven't had any malfunctions with it, and it appears to be running programs just fine.· At lower clock rates, I don't think this is an issue.....

Thanks.

Keith M
·

Paul Baker

I don't have an answer, but I do have·some questions, how long are we talking about the SX running for before you note this temperature? The regulator getting quite warm is normal, but Ive never experienced mine getting super hot. Are you adhereing to the max source/sink current requirements of the outputs for the SX?

Post Edited (Paul Baker) : 3/9/2005 5:57:25 AM GMT

KenM

It is not normal for the SX to run so hot it would burn your finger.

Even running at 50 MHz for hours......

Also, an extreemly tight loop as you say will not make the chip run warm, per se. As I understand it, the heat that is generated comes from a 'gate' making the transition from low to high or visa versa. Basically, next to no power is generated in the switching transistors when they are ON, or OFF. But during the transition from ON to OFF or visa versa, power is consumed. Running at 50 MHz, something inside the SX is making many many transitions....and those transistions = heat.

I·can say that the SX will get quite hot if an output pin is made·high, and shorted to ground, I've done it (on accident of course).

One amazing thing is that the output pin survived, that is, it after removing the short that pin still works. Don't know if it is about to fail the next second, however, but so far so good.

The SX also can run warm if pins are made inputs and left floating, but I have never had one get hot, from this activity. Nor do I allow unused inputs to float now that I am 'educated' in that area.



Post Edited (KenM) : 3/9/2005 6:16:44 AM GMT

Keith M

Thanks for the replies.

I think I improperly connected something to ground.· A few minutes after I posted this, I prompted found a miswired connection, and went to bed.· This has happened in the past, and I wasn't really able to narrow down the cause.· I'm working on a new project and am constantly disconnecting and reconnecting pins -- and so I'm sure I'm going to make some mistakes.

Is heat generally caused by either something going to ground that shouldn't be, or something that should be going to ground that isnt?· I've had other heat problems in small circuits I've built --- and they are normally related to miswiring a prototype, but maybe there is a rule of thumb here.· When I build something, I'm constantly touching the IC(I do know about·ESD·issues)·to check for heat.· This is usually a good indication something has gone wrong.

As far as source/sink goes I have port B hooked up to a 6ft cable going to a PC's parallel port.· I would imagine this wouldn't be an issue, but I'm a beginner in all of this.

Thanks.

Keith

Paul Baker

if your properly communicating on the parallel port that isnt the source. connecting any I/O pin to either Vdd or Gnd, then configuring the pin for output and driving it to the other value (1 when tied to Gnd, 0 when tied to Vdd) is bad practice (the 1 and tied to gnd isn't as big of an issue for the SX but still dont do it). Your creating a low resistance path from the + and - terminals of your supply, somewhat equivalent to taking a wire and placing it across a battery's terminals, but doing it inside·your SX!

allanlane5

It would be a good idea to put a current-limiting 220 ohm resistor in series between your SX and the parallel port. The SX can protect itself pretty well, but it does need some current-limiting device (like a resistor) in there. This should protect your PC's parallel port a little, also.