microcontroller heating problem

[nia]

hi guys,

why microcontroller temperature sometimes normal, and sometimes hot although there is no short circuit, over current etc. i use dspic30f6014a.

i suspect:
a) pull up resisor value connected to vcc - not sure suitable value
b) fuses settings?

could it be because the above or else?

[Ttelmah]

1) Short circuit somewhere..... You say not, but could be something like pulling a pin up with a 'low' resistor value, then in code programming the same pin to pull down.
2) Resistor values don't really matter. Basic rules: Low enough to genuinely bias the pins out of the transition region, but high enough to not cause problems if you do accidentally drive the pin as an output. Typically anything from perhaps 4K7 to 100K....
3) If several pins are set as inputs, and 'floating', this can make the processor run warm, if they sit in the gate transition region.
4) Fuses, probably not. How could these change to give intermittent behaviour?...
5) Something silly, like an LED, without a current limiting resistor.
5) How fast are you running?. If you are operating fast, and driving (say) a reasonably capacitive load, with a PWM output, the chip _will_ draw significant current.

Best Wishes

[temtronic]

Also consider...
putting an ammeter in the power supply to see the current. Consult the spec sheets to see if it's 'normal' for the voltage levels, speed, peripherals, etc. in your design.

Put an oscilloscope on the power supply, to check for excessive AC component, faulty capacitors, etc. Linear supplies are far less likely to cause problems than switching supplies.

How long until overheating? Seconds, minutes, hours?

Erase the chip and powerup. Does it overheat?
Reprogram with a simple 'Hello World' or loopback test, does it overheat?

Check for correct value for current limiting resistors for any LEDS you are driving from the PIC.

Check the errata sheets for your PIC, maybe you've got a bad one?

Is this a purchased PCB, selfmade, whiteboard, stich-n-solder board?

Post the schematic for more ideas.

[temtronic]

Also consider...
putting an ammeter in the power supply to see the current .Consult the spec sheets to see if it's 'normal' for the voltage levels,speed,periperlas, etc. in your design.

Put an oscilloscope on the power supply, to check for excessive AC component,faulty capacitors,etc. Linear supplies are far less likely to cause problems than switching supplies.

How long until overheating? Seconds,minutes,hours?

Erase the chip and powerup.does it overheat?
Reprogram with a simple 'Hello World' or loopback test, does it overheat?

Check for correct value for current limiting resistors for any LEDS you are driving from the PIC.

Check the errata sheets for your PIC, maybe you've got a bad one?

Is this a purchased PCB, selfmade,whiteboard,stich-n-solder board?

Post the schematic for more ideas.

[ELCouz]

I know it's an oldies but I stumbled upon some dsPIC30F6014A I had in stock.

When I try to run them at full power (30 MIPS @ 5.0V) They get very hot after a while and crash/restart on a simple led blink code.

I know it's a known issue with them (overheating).

Should I throw them in trash?

Or Microchip since have corrected the PIC revision (and replace the batch I have to a newer one)?

I know the 30F series was problematic and it's showing its age today.

But on some designs I have everything run on 5V (so no need level shifting).

Some recommends running at maximum 16 MIPS without a heatsink!
_________________
Regards,
Laurent

-----------
Here's my first visual theme for the CCS C Compiler. Enjoy!

[Ttelmah]

The version you have is marked -30L?. If not, it is not rated to go to 30MHz.
They do run hot. They dissipate about 1.25W at 30MIPS. The chip will run about 50C above ambient, if the board is not helping to move the heat away. Good thermal layer with lots of little micro links through in the board, and the case temperature plummets.

[ELCouz]