Laying components under switching regulator? - 2"x1.5" board. Space at premium.
I'm designing a 2"x1.5" board. It has a dual switching regulator based on the LT1944 for 24V and 5V, post-switching linear regulators, analog circuitry with ac coupled single ended in to diff-out, microcontroller, usb, usb lipo charger, and bluetooth. The 24V lines are for biasing sensors on the analog side. Approximately 9mA of current runs through them. I've produced a 2 layer test board using our in-house prototyping machine with just the power supply, microcontroller, and analog circuitry. It works flawlessly. The 24V lines to the sensors are point-to-point wired as to simulate them being on their own layers. The space under the regulator, on the opposite side of the board (approximately 0.8"x0.75"??) is empty as I'm afraid of switching noise being induced into other parts of the circuitry. If I use a 4 or even 6 layer board, can I place components and route lines on the opposite side of the board under the power supply? Ideally, I'd like the usb connector and lipo charging circuitry to be there as it will be close to the lipo battery. The power supply section only needs 2 layers - top layer and ground layer. Any help is appreciated.