smps pcb
I guess I don't need to tell you that page 23 of the datasheet contains some pretty helpful PCB layout info, both with an example layout as well as by showing what the high current paths are.
I've done a number of PCB layouts using LTC switchers (and others too). I certainly sympathise with your problem. The good news for the part you've chosen is that it doesn't have an integrated FET. So the high current paths into the controller are minimal, and the power dissipation of the controller is also reduced. However, keeping the feedback, compensation & other sensitive inputs as nose-free as possible is as important as ever.
From what you're describing, my guess is that your current layout may well "work", but probably work pretty badly. If you haven't physically built a PCB yet, I'd tear it up & try again. Call this one a learning exercise.
I can tell you that on the board I'm currently working on, for the rev 2 I put a *lot* more effort into the switchers layouts. And it really paid off. The switchers on the rev 2 board are much quieter than on my rev 1. Almost identical schematics, just different layouts. It's worth the effort.
My other point is to make sure you're really really clear on where the ground return currents are flowing. When dealing with switchers, it can often be a good idea to put little keepouts in the ground plane to constrain where in the ground plane those currents can flow. If you take a look at any of the LTC demo board layouts, you'll see a lot of that. Little cuts in the ground planes, so that the switcher return currents will flow in that particular portion of the plane and nowhere else. This can really reduce the coupling of switcher noise to other regions of the board.
Frank
https://www.frankvh.com