Cypress CapSense CY8CMBR2044, Design Manual

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CapSense Schematic Design
AN66308 - CY8CMBR2044 CapSense® Design Guide, Doc. No. 001-66308 Rev. *F 26
Layout Estimator
The Layout Estimator provides the minimum button size and maximum trace length recommendation based on the
intended end-system requirements and industrial design. The inputs include the overlay material, overlay thickness,
and trace capacitance of circuit board material. Refer to
Figure 3-13, Table B, to learn the dielectric constants for
different overlay materials and the trace capacitance per unit length for different PCBs. Table A calculates the
minimum button diameter and maximum trace length for the design, based on three relative ranges of system noise.
Low, medium, and high noise is a relative figure of merit to help you with button development. Noise conditions can
vary button to button based on the end-system environment. If the noise conditions are unknown, use medium noise
conditions as the starting point. The actual noise seen at each button will be determined in the design validation step
described in
Design Validation.
Use the outputs of this sheet to guide the sensor board layout process and then check the design prior to prototyping
with the C
P
, Power Consumption and Response Time Calculator sheet as detailed Cp, Power Consumption and
Response Time Calculator .
Figure 3-13. Layout Estimator
Inputs:

Overlay thickness

Overlay dielectric constant

Capacitance of trace per inch of board
Outputs:

Recommended minimum button diameter and maximum trace length for different noise conditions

Button to ground clearance
Note The button diameter of each button can be different in the design based on whether the noise varies button to
button.