Do not mess up the nice island we've come up with for your MCU analogue inputs by placing this other chip in the manner shown. In looking at the device you have added I'd suggest that you would be best off making another separate island structure for this device.

From other posting where you talk about 2 layer board....forget about that and use 4 layer board. Two layer board would only be applicable to design where you intend to make 100K units and you can afford to tweak the design through 4 or 5 fab spins and have the benefit of a very experienced analogue engineer working on your team.

From other discussion regarding the placement of the GND bridge and making consideration for the fact that the OSC pins are right next door....I suggest pulling the bridge over under the chip somewhat and then bring the ferrite filters as close to the MCU pins as feasible. It is not possible to avoid near contamination of the GND plane from OSC since this is already happening on board the chip itself. This is why I suggest to place the VSS pin of MCU and the near by VSS/VDD filter caps close to the center of the GND bridge so no funny current circulation is created on the PC board due to returns back to the OSC structure. If you push the plane split away from the MCU GND pin there will be some small loss of performance of the analogue portion.

This chip is FAR from optimum with regard to the place that the OSC is located. If one has any doubt about it then the immediate reaction should be to toss the MCU away and select another style that has separate AVSS and AVDD pins. There are many MCUs available to select from!!!

Michael Karas