Hi, ok first I cant imagine why lots of other people dont have this problem, maybe its just my bad circuit design. :?
I could only find one other post of someone who couldnt get his micro to run after power up.
Heres his post, but he never really found a solution:
And on a side note how does one do an exact forum search (if possible?), like in google you would type "power up"?
Ok if you see my schematic its nothing special, a small 5V SMPS, then a low drop out 3.3V regulator. My circuit has quite a few filters as per the suggestion of the app notes. Then the 3.3V is feed through a filter right next to the AVR (ATmega8515L, running at 3.6864MHz) to its Vcc. If I check the AVR Vcc at turn on it seems pretty instant visually speaking on my multimeter. I cant tell you in ns!!
What happens is the micro doesnt run when you power up. After alot of probing around, and wrong turns into dead avenues (enabled brown out detection 2.7V, enabled CKOPT, played with every SUTCK_SEL option, using the longest start up option).
The only issue I could see, was the small filter that powers the micro would delay the power supply rise longer than the reset. So I thought I will power the Reset from the AVR Vcc rather than the +3.3V line. I cut the track and resoldered it, no improvement.
Even when I connect Reset to VCC, it doesnt generate the "power on reset", which the datasheet says it will.
On the reset circuit, if C12 is your good old 100nF it doesnt work. The only way I could get the micro to run after a power up reset was too stick a ridiculously sized cap there. Anything less than 100uF was not consistant, so I'm using 150uF.
I think just throwing this large cap at it is just masking the problem. I dont like to do band aid fixes. Can anyone see anything I am possibly doing wrong? Are there other setting I should try?
Thanks for any advice!