PIC 12F509 begins to heat at power up

[Pedro Pinto]

Hello

Have anyone a idea what happens.
I have a board with a 12F509 and sometimes when power up the circuit
it begins to heat up and all the IO's are high.
I programm it with intern RC oscilator and the MCRL pin as digital IO
As i said it just happens sometimes.

Thanks for any idea
Best regards
Pedro

[mackrackit]

What do you have connected to the PIC?
Do you have TRIS? statements at the beginning of your code to control the pin's direction?

[Acetronics2]

Hi,

I got such a surprise , years ago with a 16C84 ... ( Andeas Voggender R/C Esc , showns in Elektor Magazine - project 960095-11 ).

While receiving too much glitches, the PIC begins to heat ... one and only solution : power OFF !!!

No overloaded output ...

Back to the " constructive " side ... you must take great care to the config sequence of your PIC, and especially to the reset circuitry.

When the device starts normal operation (exits the
reset condition), device operating parameters (voltage,
frequency, temperature, ...) must be met to ensure
operation. If these conditions are not met, the device
must be held in reset until the operating parameters are
met

these lines are "not so innocent" ...

see Datasheet related pages for that ...

Alain

PS : could you join the " faulty " program ???

[Pedro Pinto]

Hello Acetronics

I think the problem is the Pic itself. I have until 2 years ago 1000 boards that
have not this problems, for 4 Months have make more 200 units and receive 6
boards back from customers that have this problems.

The init part of the code is very simple

sorry, this a original init code, the previous was experiments

DEFINE OSCCAL_2K 1
'
sepic_ok var GPIO.3        
call_shutdown var GPIO.4
sepic_on_off var GPIO.5
pulsador var GPIO.2
am_on_off var GPIO.1
'sense var GPIO.0
'
TRISIO = %11001111
'
low sepic_on_off        
low call_shutdown       
'						
ciclo var word
conta var byte 
conta2 var byte
flag_pulsador var byte 
'			
DEFINE DEBUG_REG GPIO   
DEFINE DEBUG_BIT 4
DEFINE DEBUG_BAUD 2400
DEFINE DEBUG_MODE 1          '1= direct to pic
DEFINE DEBUG_PACING 1000			
'

	DEBUG "V1.1 08/07",10,13
'
pause 500    'estabilise

ini:low call_shutdown   
ciclo = 1:pause 10
if pulsador = 1 then ini   
 for ciclo = 1 to 100      ' "debounce"
  if pulsador = 1 then ini
   pause 1
 next ciclo 

'Learn if it a switch or a press button
inicia:  
High sepic_on_off        'set Buck/Boost on
 pause 1000              
 for ciclo =  1 to 50    'test if the Buck/Boost works
   if sepic_ok = 0 then 
   for conta = 1 to 100
    pause 10
    if sepic_ok = 1 then learn
   next conta
   low sepic_on_off       'sepic not OK, shut down
    pause 3000
     goto ini
   endif

The rest of the code is a loop to look for shut down by the user or if the sepic not working

Best regards
Pedro

[mackrackit]

Bad set of boards. Seems pretty clear now.

[Pedro Pinto]

Hello mackrackit
What do you mean?
Bad set of boards. Seems pretty clear now.


Regards
Pedro

[ErnieM]

Pedro,

OK, so GP4 and GP5 are the outputs, the rest are inputs. Each output has a 1K resistor, so the max that goes into/out of there is 5/1K or 5mA each output, 10 mA total. 10 is well within any PIC limit. That isn't where the problem is.

In your original post you state the problem happens "sometimes." Does this mean a particular part will sometimes fault, or sometimes several parts in a lot will fault but each will fault every time?

Do you do any testing before shipping? If you have customer returns after test then the parts seem to have worked at least once.

[Pedro Pinto]

Hello ErnieM

Thank you for help
With the first 1000 boards two years ago i have not receive back one board with this problem.
For 3 months i have make 220 same boards, same software and now received
back from coustomer 6 unit with this problems. I have order a few Pic's now to test with this new order serie. I will hope, it helps, than i have no more ideas what can be that. In this moment i think that it is the Pic. I post feedback when i receive the news pic's

Best regards
Pedro

[Ingvar]

Pedro,

Have you checked that all resistorvalues are what they should be? It happens that resistors are faulty, or most common, wrong value was fitted at manufacturingtime. There could also be a short across a resistor thus making it zero, this not easy to spot if it's underneath the resistor. There is also the possibility that the PIC have experienced a nasty shock that makes a pin stuck at high or low level, even when it shouldn't be. I've seen them all over the years. Lucky for you, your board isn't so big, you should be able to measure all possible combinations.

/Ingvar

[ErnieM]

Always helps to go back to the definition of the problem:

Hello
Have anyone a idea what happens.
I have a board with a 12F509 and <b>sometimes</b> when power up the circuit it begins to heat up and <b>all the IO's</b> are high.

Questions:

Does <b>"sometimes"</b> mean some units all the time or any unit some of the time? Do the bad units fail every time or not every time?

Does <b>"all the IO's"</b> really mean all? GP0 to GP4 are normally at 5V at turn on as they have their pull-up resistors to 5V. How close to 5V are they? Same voltage to a millivolt or so or are they measurably lower or higher? (If different that tells us where current is going, the amount of difference tells us how much current).

And when failing, are Vdd and Vss still normal?