I populated the back(power supply side) of the board and it WORKS!
The idle current of the lt1618 regulator is at 8-10 mA as opposed to the 2 mA in the simulation (at 60 uA load), and 18mA at 1 mA load. The efficiency is bad as expected, a little over 50%. This, however, is in line with the simulation if the higher than expected idle current is taken into account. The datasheet 5v-to-5v (USB) at 500mA circuit only claims 75% efficiency, and I am working with only 100mA and a variable input voltage. The input current regulation is within +-10%, also as expected. The ripple is <5 mV, better than the simulation. Overall, it does the job. This is not really meant for the task I am using it for, so the simulation may not be right, but I still suspect something is not quite right with the real-world circuit. It will do for now, though.
The lt1615 is just being plain awesome, though! 60uA at idle, exactly as expected.
I have not done extensive efficiency measurements, but it appears to be in line with the simulations at about 80% Ouch, I was wrong -- I am only getting 64% efficiency at 16mA out, 5v in (I think), and simulations only show about 72%. What did I do to convince myself it was supposed to be 80% (I figured it out. The specific inductor used was different between my earlier simulation and my current one). This little guy was selected because it can convert between 1 and 5 volts to 3.4 volts
at 80% efficiency with microamp idle current, a task at witch it seems to preform admirably despite the FB trace under the inductor (I'll fix it in the next board rev -- I knew better, but somehow let it slip)
I think I will toss the 1618 in the next board rev, even though I might be able to lower Iq with better layout(The current layout looks really good, though. Maybe the converter attached to it's output is messing with the feedback loop because output filtering is insufficient?), because LT just released the LTC4120 "Wireless Power Receiver and 400mA Buck Battery Charger". Don't you hate it when you are designing a complex circuit and then somebody releases a one-chip solution
Overall, for my first surface mount board with anything smaller than a SOIC, or more than 2 SMT parts, and also my first two switching regulator layouts, I am just happy to see it work!
Pics coming soon