To conserve PCB area, a 4 layer stacked coil approach is used with the sense coil on the top 2 layers and reference on the bottom 2 layers. The LDC0851 switching threshold is then determined by following parameters:

1. Conductive Target Size: The best response is achieved when the target area is ≥100% compared to the coil area.
2. Coil diameter: The diameter of the coil should be at least 3x greater than the desired switching distance.
3. ADJ code: Increasing ADJ code linearly scales down the switching distance estimated by Equation 1.

The coil diameter should not exceed the diameter of the conductive target of 10mm in order to keep the target-to-coil coverage ≥100%. Additionally, in order to detect the lightest button pushes where the conductive target rests at a height of 2.5 mm, the coil should be at least 3 times greater giving a minimum size of 7.5 mm. The user may therefore select a coil size between 7.5 mm and 10 mm. A coil diameter of 10mm is chosen for the most flexibility and tuning range. The response versus ADJ code is shown below in Figure 7-5.

In this example the deflection caused by the button press (∆d) is 2mm. Note that the ∆d must be enough to cross the “Switch ON” threshold and return past “Switch OFF” threshold of the LDC0851 for a given ADJ code to be considered a valid code. Codes 0 through 6 should not be used because the conductive target has already crossed the "Switch ON" thresholds and would always be in the ON state without a button push. Similarly code 15 should not be used because the output would always be in an OFF state regardless of how hard the button is pushed. Therefore codes 8 through 14 are clearly inside the travel distance of the button. Select code 8 to detect light button pushes, code 11 for medium button pushes, or code 14 to only detect strong button pushes. Once the ADJ code is selected based on user preference, set the resistor divider R1 and R2 values according to section Setting the Threshold Adjust Values.