Author Topic: ATmega TQFP package overheating  (Read 16472 times)

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Online Simon

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ATmega TQFP package overheating
« on: September 06, 2013, 05:22:47 pm »
I've made up a board with an ATmega328P-AU (TQFP package). It has one analog in and one PWM out (yes waste of a chip and yes arduino based).

Problem is that the MCU is getting VERY hot and drawing about 290 mA and the 5V has dropped to 3.3Vish because i have a series resistor on the regulator to help limit current like this. There are no shorts of any of the I/O's used and i've not been able to program it (via AVRISP from the arduino IDE), it comes out with:

avrdude: verification error, first mismatch at byte 0x0000
         0x0c != 0xff
avrdude: verification error; content mismatch

Any idea's ?should I try the excruciating experience of removing the MCU ?
 

Offline mmagin

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Re: ATmega TQFP package overheating
« Reply #1 on: September 06, 2013, 05:33:45 pm »
That you cannot ISP program it suggests that one of those lines is shorted to ground or Vcc.  I'd inspect the soldering carefully.
 

Offline firewalker

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Re: ATmega TQFP package overheating
« Reply #2 on: September 06, 2013, 05:45:25 pm »
Is it an AVR chip for sure (genuine)?

Alexander.
Become a realist, stay a dreamer.

 

Online Simon

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Re: ATmega TQFP package overheating
« Reply #3 on: September 06, 2013, 05:50:58 pm »
yep, bought from RS, turned up on a massive tray for 5 chips ;)
 

Offline madires

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Re: ATmega TQFP package overheating
« Reply #4 on: September 06, 2013, 05:52:09 pm »
Some I/O pins must be sourcing or sinking a lot of current (the limit is 40mA per pin). By default the I/O pins should be in HighZ mode, so there's something very wrong.
 

Online Simon

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Re: ATmega TQFP package overheating
« Reply #5 on: September 06, 2013, 05:54:14 pm »
quite, I have 200 ohms on the 5V line which is a bit odd but them with no power the chip will give different readings. 200 ohms is 25mA so not sure where the attempt to draw over 300mA comes from
 

Offline firewalker

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Re: ATmega TQFP package overheating
« Reply #6 on: September 06, 2013, 05:58:30 pm »
As I saw the pin out for the TQFP is GND-VCC-GND-VCC. Could be a short circuit among those.

Alexander.
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Online Simon

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Re: ATmega TQFP package overheating
« Reply #7 on: September 06, 2013, 06:00:16 pm »
nope, that would not make the MCU overheat just the regulator. the resistance from GND to VCC is 210 ohms
 

Offline firewalker

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Re: ATmega TQFP package overheating
« Reply #8 on: September 06, 2013, 06:05:57 pm »
No, it would not. So... Try another chip.  :-/O :-/O :-/O

Could the chip got damaged during soldering?

Alexander.
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Offline madires

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Re: ATmega TQFP package overheating
« Reply #9 on: September 06, 2013, 06:09:56 pm »
Maybe an inappropriate question :-), but do you got the chip orientation right?
 

Online Simon

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Re: ATmega TQFP package overheating
« Reply #10 on: September 06, 2013, 06:10:40 pm »
Maybe an inappropriate question :-), but do you got the chip orientation right?

A very valid one for a square package. Yes it is on there right
 

Offline madires

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Re: ATmega TQFP package overheating
« Reply #11 on: September 06, 2013, 06:15:21 pm »
Pull-up resistor for the reset pin?
 

Online Simon

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Re: ATmega TQFP package overheating
« Reply #12 on: September 06, 2013, 06:16:55 pm »
I have one.

i attach the schematic for everyones amusement
 

Offline jahonen

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Re: ATmega TQFP package overheating
« Reply #13 on: September 06, 2013, 06:17:35 pm »
Could it be as obvious as just incorrect pinout (schematic symbol or PCB footprint error)? Worth to check actual board VCC and GND pins against datasheet.

Regards,
Janne
 

Online Simon

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Re: ATmega TQFP package overheating
« Reply #14 on: September 06, 2013, 06:19:03 pm »
yes I have done that.
 

Offline madires

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Re: ATmega TQFP package overheating
« Reply #15 on: September 06, 2013, 06:26:22 pm »
I have one.

i attach the schematic for everyones amusement

Seems to be fine. The only thing I saw is that AVcc isn't connected to Vcc. It should be connected even if the ADC isn't used.
 

Online Simon

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Re: ATmega TQFP package overheating
« Reply #16 on: September 06, 2013, 06:27:06 pm »
ok, could it cause a problem like this ?
 

Offline madires

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Re: ATmega TQFP package overheating
« Reply #17 on: September 06, 2013, 06:32:13 pm »
ok, could it cause a problem like this ?

Actually it shouldn't.
 

Offline amyk

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Re: ATmega TQFP package overheating
« Reply #18 on: September 07, 2013, 12:36:00 pm »
Did you take ESD precautions?

Try another chip.
 

Offline Psi

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Re: ATmega TQFP package overheating
« Reply #19 on: September 07, 2013, 12:53:39 pm »
I've seen ATMega's get hot when they have been damaged.
I once put 12V onto VCC when some wires rubbed together for a split sec. After that the current jumped up by a massive amount and it never worked again.

I highly suspect your mcu is dead.

« Last Edit: September 07, 2013, 12:55:12 pm by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Online Simon

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Re: ATmega TQFP package overheating
« Reply #20 on: September 07, 2013, 02:27:25 pm »
Did you take ESD precautions?

Try another chip.

nope, good point
 

Online Simon

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Re: ATmega TQFP package overheating
« Reply #21 on: September 07, 2013, 03:59:23 pm »
Well i took it off and found the (SOIC) regulator supplying 6.8V ! so i replaced the reg and still supplying 6.8V! replaced with a standard through hole 78L05 and now outputs 5.25V, Someone at Farnell is in for a bollocking !
 

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Re: ATmega TQFP package overheating
« Reply #22 on: September 07, 2013, 04:33:22 pm »
Reversed pinout? Do they make helpful LM78L05R parts? ;)
 

Online Simon

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Re: ATmega TQFP package overheating
« Reply #23 on: September 07, 2013, 04:35:45 pm »
well I followed the datasheet pinout. Not my problem.
 

Online Simon

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Re: ATmega TQFP package overheating
« Reply #24 on: September 07, 2013, 05:47:19 pm »
right, put another atmega on there and still overheats and now my reg is at 7V  again! this is the TO-92 version, how on earth can an ATmega cause a reg to up it's voltage ?
 


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