Bergamot wrote:Yeah, I forgot to mention that the design is completely through-hole. and that the main reason I wanted to use a power plane was design simplicity.
It seemed to me that it should work from a digital perspective, since it shouldn't matter much what shape the chunk of metal is in as long as it isn't too small, but I wanted to make sure there weren't any analog factors i was overlooking.
Ground and power planes can create problems, more so in high speed digital circuits and many analog designs. The issue is adding capacitance that slows down digital edges. The drivers have to work harder to overcome the capacitance, and this increases the required input power (while doing nothing for the overall performance).
Planes can also allow coupling of strong signals into sensitive analog low power nodes. Op Amps and Oscillators in particular are susceptible to ground plane abuse. Here's a snip it form an earlier thread:
bigglez wrote:The most important thing is not to add too much capacitance (with large ground planes) as it may stall the oscillator. Such a problem is very hard to fix (spin the PCB design...)
Next on the list is to keep all other signals away from the RTC Xtal pins for fear of coupling in noise.
Finally, if you are looking for accuracy add a small trimmer cap across the crystal. Once the pads are in place you have the option of deleting the trimmer, but adding one after the fact is not so easy.
Take a look at the Dallas/Maxim app. note number 58, here.
Here's a layout I'm using for the DS1307 (8SOT) version (Battery back up and 1PPS led, I2C bus pull up and matching resistors):
On a double-sided 0.063 thick PCB (BatchPCB for example) the ground plane on the bottom layer will be okay. Thinner boards (or multi-layer with internal ground planes) are a problem.
Read the whole thread here