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Atmega8 outputs - very low current

 
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Big_Valven

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Joined: 26 Jun 2007
Posts: 24

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PostPosted: Tue Jul 10, 2007 9:11 am    Post subject: Atmega8 outputs - very low current Reply with quote

Hi all,
I am having a curious problem with an atmega8 where all pins, when used as outputs, measure as they should when unloaded and measured with a digital multimeter, but as soon as I connect a load of any sort they will measure 0v. I cannot even light an LED.
I haven't had this problem before and I'm a little confused as to why it's happening. Any ideas?
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Big_Valven

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Joined: 26 Jun 2007
Posts: 24

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PostPosted: Tue Jul 10, 2007 9:20 am    Post subject: Reply with quote

Also, I forgot to mention that I have a strange symptom that I have voltage on the serial transmit line (the other device idles high) and when I remove supply voltage the atmel continues to run because of the voltage on this pin. why is this?
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ex4

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Joined: 13 Jan 2006
Posts: 1064
Location: indonesia

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PostPosted: Tue Jul 10, 2007 9:58 am    Post subject: Reply with quote

that very odd,i my self had this problem, and to be honest with you, i throw away the chips, since in my opinion the port is useless anymore (my PB all dead on ATMEGA32 once, dont know why till now?? Question Question )
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Big_Valven

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Joined: 26 Jun 2007
Posts: 24

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PostPosted: Tue Jul 10, 2007 10:08 am    Post subject: Reply with quote

So you think it's actual damage to the chip? I'll try it on a known working test board and see what happens. Any clues to why the serial lines can power the device?
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Jonas

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Joined: 06 Jul 2006
Posts: 109

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PostPosted: Tue Jul 10, 2007 10:38 am    Post subject: Reply with quote

Hey

Its no strange that the chip continues to run. Check page 51 in the Mega8 datasheet.

It got protection diodes to ground and VCC.


/Jonas
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Skragan

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Joined: 09 Sep 2005
Posts: 16

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PostPosted: Tue Jul 10, 2007 1:30 pm    Post subject: Reply with quote

Chip may be damaged due to latch up fault (pins connected to power without supply connected) ? Are you sure, regular supply is connected ? Or are the port pins being driven by power through protection diodes ? Do you have a filter with a resistor at vcc ? Resistor to high ?

As Jonas said, the power can go through the protection diodes, but this can damage the chip.

Regards
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subar

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Joined: 31 May 2007
Posts: 142
Location: kurdistan region

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PostPosted: Tue Jul 10, 2007 4:17 pm    Post subject: Reply with quote

hi
i advice to :
1-use another ATMEGA8 to figur out the problem so if you find that the problem is the same , the case is one of the following :
a- you did not use resistors between the output pins or the resistors have low value which is the cause of polling to much current and fall down the voltage and the output pins of the microcontroller.
b- the power supply current is low which is now enough to supply all the drivers that you connect them to the microcontroller.

2- if the problem is appeared that means the chip is damaged and you should change it.

_________________
many people know what to do,But few people do what they know.

Regards
subar
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