Author Topic: ATmega TQFP package overheating  (Read 16230 times)

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Offline 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 ?
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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.
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Offline 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 ;)
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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.
 

Offline 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
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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.

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Offline 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
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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?

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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?
 

Offline 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
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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?
 

Offline 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
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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
 

Offline 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.
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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.
 

Offline 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 ?
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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.
 

Online 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)
 

Offline 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
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Offline 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? ;)
 

Offline 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.
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Offline 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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