Forum: µC & Digital Electronics internal current draw on reset pin (ATMEGA48 20AU)

von Michael (Guest)

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Hi there

My ATMEGA48 resets itself unintentionally all 0.1 to 4 seconds at random 
and after a while stops working at all.

The software is not expect to be the reason. I reduced it to minimum and 
the same problem still occurs.

The supply voltage is 3.3V and batterypowered with a 10uF capacitor in 

I have connected a 10k pullup to Vcc and a 100nF capacitor to GND on the 
reset pin. There is nothing else connected to the reset line. Just the 
pullup resistor, the capacitor and a 6 pin connecter for the MKII 

If I measure the voltage on the reset pin with a oscilloscope there is a 
voltage level of something as low as 0.8V to 1.3V without any worse 
noise or spikes as long as it is not working properly. The uC does not 
start because it's reset at the same moment again.

As soon as I connect the reset pin with a copperwire hard to vcc the 
ATMEGA still almost resets and the LEDs start to flicker a bit.

So it seems to me that the reset pin draws a lot of current. (Measured 
up to 20mA!)

The first time a day I connect the system to the battery it works fine 
for some minutes but then it's getting worse every time i connect it to 
the battery again.

Have you ever heard of such a behaviour? I would be very pleased if you 
could give me a hint.

I've tried to solve this strange problem for about two weeks but 
regardless of all my efforts it's still not working.

von Hugo (Guest)

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Hi Michael,

I had the same behaviour at a 5V Mega168.

The reason was, that i overpowered the device by the summary of the
sink current on the digital outputs.

maybe it helps


von Michael (Guest)

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Hi Hugo

Thanks a lot for this information. This is most likely the reason. The 
maximum sink current is indeed as high as about 300mA in rare 

The funny part about it is that from one day to the other all boards 
suddenly worked. And I haven't changed anything. Not the hardware nor 
the software was modified.


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