Author Topic: ATmega TQFP package overheating (Read 21267 times)

firewalker · « **Reply #25 on:** September 07, 2013, 05:56:44 pm »

Is the regulator ok? If the micro is somehow sorted it could easily kill the regulator causing a voltage rise. Also an error in the regulator circuit could overheat a micro.

ben7 · « **Reply #26 on:** September 07, 2013, 06:02:53 pm »

What is connected to the PWM pin?

Is the Vref pin connected to 5v? If it is, that might be the issue. You can short out the internal reference voltage.

What kind of a power supply are you using?

I had someone give me an arduino uno that was broken. The arduino unos have a major fault where the 3.3v regulator can short out, and the 5v regulator will give out around 6-7v!
(This is not from an excessively high 3.3v rail - the 3.3v rail was infact lower than 3.3v - and the arduino was fed the correct voltage when it died)

Simon · « **Reply #27 on:** September 07, 2013, 06:05:03 pm »

well showing 2-3K on the 5V output (reg+ MCU) the short happens when the atmega gets power, I can't control what goes on inside the damn thing ! particularly when it is not even programmed yet

Simon · « **Reply #28 on:** September 07, 2013, 06:12:15 pm »

Quote from: ben7 on September 07, 2013, 06:02:53 pm

What is connected to the PWM pin?

Is the Vref pin connected to 5v? If it is, that might be the issue. You can short out the internal reference voltage.

What kind of a power supply are you using?

I had someone give me an arduino uno that was broken. The arduino unos have a major fault where the 3.3v regulator can short out, and the 5v regulator will give out around 6-7v!
(This is not from an excessively high 3.3v rail - the 3.3v rail was infact lower than 3.3v - and the arduino was fed the correct voltage when it died)

Vref is unconnected, the PWM is connected to a 2N7002 mosfet gate. the supply is a plug in adapter that delivers a so called 12V but 22v in reality, then a 470R resistor in series with the blessed 5V regulator.

Simon · « **Reply #29 on:** September 07, 2013, 06:34:17 pm »

I'm on the verge of replacing the stupid atmega with a tiny in DIP if neccessary, just don't get this behavior

Simon · « **Reply #30 on:** September 07, 2013, 07:08:05 pm »

well I got my code to load

Simon · « **Reply #31 on:** September 07, 2013, 07:12:48 pm »

right, it starts at 5V and then after a few seconds suddenly starts climbing - I pulled it at 8V !, zener reg required ? after all current consumption is pretty predictable !

Monkeh · « **Reply #32 on:** September 07, 2013, 07:18:16 pm »

There's something wrong with your regulators. Try with a proper current limited supply.

What regulators are you using, exactly?

Simon · « **Reply #33 on:** September 07, 2013, 07:22:06 pm »

Well using a 78L05ACZ from ST, also used the soic version. this is getting ridicolous, the voltage was fine until the Atmega went back in.

Monkeh · « **Reply #34 on:** September 07, 2013, 07:28:35 pm »

Well either you've got faulty regulators, faulty micros, or you're killing the regulators with heat and/or excess input voltage. It's easy enough to work your way through those problems, starting with just running the circuit from a current limited supply which won't kill your micro.

Simon · « **Reply #35 on:** September 07, 2013, 07:38:14 pm »

sadly don't have one.

Simon · « **Reply #36 on:** September 07, 2013, 07:52:44 pm »

well i put a 5.1V zener in front of the damned regulator and it still climed to 6V!!!!!!!!, the MCU is still overheating. This is getting ridiculous, how many times will the PCB withstand these stupid mega's being removed and re-soldered ?

chrome · « **Reply #37 on:** September 07, 2013, 07:55:37 pm »

Where does the PWM output go to?

Also the voltage starts climbing because you are loading a 100mA Regulator with 300mA (at 22V input no less).

Simon · « **Reply #38 on:** September 07, 2013, 08:04:23 pm »

The PWM outpuit goes to the gate of a mosfet. I put a 5.1V zener in front of the reg and it still outputted 6+V which as far as I know is impossible.

I have 1.65K in series with the reg and the 5.1V zener in parallel, so there is no way the regulator is getting so much input voltage (it should in fact crash and go into limp mode at about 3V) and the current is being controlled.

just trying to remove the atmega to try yet again

chrome · « **Reply #39 on:** September 07, 2013, 08:07:16 pm »

How about actually measuring the voltage on the input of the Vreg.

And I mean where does the actual output of the PWM go to (as in the FET itself).

Simon · « **Reply #40 on:** September 07, 2013, 08:10:19 pm »

To the gate, the voltage from the zener goes straight to the reg input past a capacitor so unless a peice of track and a capacitor can become a boost converter this is getting bonkers. just trying another MCu after some more measurements on the reg

Simon · « **Reply #41 on:** September 07, 2013, 08:16:53 pm »

Well 5.14V on the zener, 4.67 after the reg. Looks pretty civil, will it all suddenly turn into a mysterious voltage multiplier when i put the atmega back in ?

chrisbrown · « **Reply #42 on:** September 07, 2013, 08:25:23 pm »

What's the AC pk-pk on the regulator's output? I'm wondering if too high of a current-limiting resistor is causing the regulator to oscillate.

Simon · « **Reply #43 on:** September 07, 2013, 08:28:28 pm »

The voltage is 21V about 9mA through 1.65K. I think I'm going to remove the reg and run on the zener only

chrome · « **Reply #44 on:** September 07, 2013, 08:37:31 pm »

WHAT IS CONNECTED TO THE OUTPUT FROM THE FET, what are you actually driving with the FET.

Simon · « **Reply #45 on:** September 07, 2013, 08:40:56 pm »

A resistor, like I said before the problem arises when there is not even a program in the MCU, I guess the reg might be oscilating. I'm trying a zener reg now (originally it was going to be a primary stepdown / spike protection).

Simon · « **Reply #46 on:** September 07, 2013, 08:55:06 pm »

right the atmega still overheats (with just 9mA available). i am totally lost here. are there any basic connections this mcu requires ? at this rate it would have been faster to put a dip8 attiny in on a socket that I pre program

senso · « **Reply #47 on:** September 07, 2013, 09:08:57 pm »

Never had such a problem with an atmega...
Can you show the schematic/pcb art, and maybe a photo of the thingy assembled?
21v is a bit on the high side, but for such a small load the regulator should work perfectly.

Simon · « **Reply #48 on:** September 07, 2013, 09:15:43 pm »

schematic and pcb attached

ovnr · « **Reply #49 on:** September 07, 2013, 09:53:11 pm »

Have you considered the possibility that you're feeding a higher voltage than 5V into the micro from one of the other pins? Say, "Temp IN" or "PWM out"? (In the case of "PWM out", just try desoldering the transistor and see if that does it - you might have blown the transistor, which is shorting "PWM out" to the gate, and thus into the micro)

Because it sure sounds like you are feeding a higher voltage in; if you're seeing >5v and impossible power dissipation in the circuit when your regulator only gets a little power, and then the problem goes away if you remove the chip... I'd vote on the IO pin protection diodes conducting a higher voltage to Vcc on your micro, which backfeeds the regulator (which may well blow it too!).

Are you testing the circuit with only two wires hooked up to the board, namely Vin (to the reg) and gnd? If not, disconnect EVERYTHING else, including the ISP programmer, and see if it still does it.

Edit: Note that if your chip has ever done it (conduct enough power to heat it up via the protection diodes), it may be blown and will continue overheating even with the fault cleared.
Also, if this doesn't solve it, check EVERY pin on the micro for shorts to ground or Vcc - even if it's not programmed, it might (not familiar with AVR) be driving some pins.


EEVblog Main Site	EEVblog on Youtube	EEVblog on Twitter	EEVblog on Facebook	EEVblog on Odysee

Author Topic: ATmega TQFP package overheating (Read 21267 times)

Share me