Hello Fellow Freaks!
So I've got my small handheld game console made (home brew double sided PCB). Now everything seems to work properly except for one major issue.
The device only seems to run for a small amount of time before it would appear that the device resets continuously. It seems to be anywhere in the range of 15-60 seconds after immediately removing the power supply. If I leave the device off for about 5 minutes and then turn it back on, it seems to be more in the range of 3 or more minutes before this starts to happen.
The CPU is a ATmega644p TQFP clocked at 20 MHz with a 5 volt power regulator. It is currently powered by an 11.1 volt Lithium Polymer battery.
I have checked the fuses to ensure that Watchdog and Brown-Out is disabled. So as far as I can tell, it shouldn't be caused by either of these.
If I probe the regulator output voltage, I get a steady 5.0 volts when the device is working properly. Once it begins resetting (I am unsure if I should be calling this reset, as I am unsure that is what is happening), it will begin to dip down below 5.0 volts (sometimes as low as 4.4 volts) and then back up to 5.0 volts. If I probe the supply voltage (before and during the erratic behavior), I get a steady voltage of about 12.57 volts (after a full charge) and it never seems to dip like the regulated voltage. The maximum input voltage of the regulator is 15 volts and has a 1.2 volt dropout.
Here's a couple ideas I have. What are you thoughts?
- I have do not have any by-pass capacitors for the GLCD power pins (pin #2 and #19 of header SV2). Could this cause such a voltage drop and cause a power-on reset?
- Is the 10 uF capacitor (C8) on the supply voltage of an acceptable amount? If not, could it be causing this behavior?
I am really not sure how to continue debugging this problem. I believe it's most likely an electrical issue. I have attached the schematic, top and bottom board layers, and an image of the board when it is working properly.
Any ideas of what I should try here?