I am using a Linear Technologies LT-1534 part an need to create a planar PCB surface inductor with the specific value of 28nH; i.e., the inductor will be a copper trace on the PC boards Top Surface to have a value equal to a discrete inductive component, that value to equal 28 nano Henries +/- 10%.
What formula should I use to calculate the Planar Inductor's geometry that will enable me to achieve this specific value?
The PCB's layer stack up is a 4-layer board with Top & Bottom Signal Layers, Components on Top only, with Ground Plane and Power(s) Plane on Layers 2 & 3 respectively.
The system is powered by a LiPo battery.
I have designed Printed wiring boards for many years (over 30) and have done Multi-layer Planar Transformers before, but have not had such a specific inductor value on a single layer come up as a requirement before and am a little stumped as to where to start.
The circuit goal is to design a local RCL filter for the LT1534, where the capacitive and resistive elements are comprised of discrete passive leaded components, but because of size constraints as well as the small value of inductance required, the design engineer feels that the goal would be better achieved using a Planar inductor, rather than a discrete, even surface-mount component element.
The target PCB material is FR4@0.063" thickness, one-ounce clad to between 1 1/2-2 oz finished, to be determined by other targeted trace impedances and controlled impedance transmission line requirements.
Please let me know if more specific information is required to make an educated reply, or if a schematic of the sub-circuit which contains the inductor in question is needed to make a proper assessment of the formulas required for the PCB inductance to be specified.