Cypress CapSense CY8C20x36 Podręcznik Użytkownika Pobierz pdf (Strona 52)

52 Document No. 001-64846 Rev. *I Getting Started with CapSense

Button diameter can range from 5 mm to 15 mm, with 10 mm being suitable for the majority of applications. A larger

diameter helps with thicker overlays.

Annular gap size should be equal to the overlay thickness, but no smaller than 0.5 mm, and no larger than 2 mm. For

example, a PCB layout for a system with a 1-mm overlay should have a 1-mm annular gap, while a 3-mm overlay

design should have a 2-mm annular gap. The spacing between the two adjacent buttons should be large enough that

if one button is pressed, a finger should not reach the annular gap of the other button.

3.7.5 Slider Design

A typical slider pattern is shown in Figure 3-30. The recommended dimensions for slider design are in Table 3-6.

Figure 3-30. Typical Slider Pattern

Table 3-6. Slider Dimensions

Parameter

Min

Max

Recommended

Width of the Segment (A)

1.5 mm

4 mm

Equal to overlay thickness, but within the min/max limits.

Clearance between Segments ( B )

0.5 mm

2 mm

Equal to sensor to ground clearance

Height of the segment ( C )

7 mm

15 mm

12 mm

When any segment is scanned, the adjacent segments are grounded. To maintain uniformity, the two segments on

both ends of a slider should also be grounded. Therefore, for a design with a slider of ‗n‘ segments, there must be

actually n+2 segments. If the hatch around the slider is shielded instead of ground to achieve water tolerance, then

the last two segments should also be shielded. For more information, see Shield Electrode and Guard Sensor.

3.7.6 Sensor and Device Placement

 Minimize the trace length from the CapSense controller pins to the sensor pad to optimize signal strength.

 Mount series resistors within 10 mm of the controller pins to reduce RF interference and provide ESD protection.

 Mount the controller and all other components on the bottom layer of the PCB.

 Isolate switching signals, such as PWM, I

C communication lines, and LEDs, from the sensor and the sensor

PCB traces. Do this by placing them at least 4 mm apart and fill a hatched ground between CapSense traces

and non-CapSense traces to avoid crosstalk.

 Avoid connectors between the sensor and the controller pins because connectors increase C

and decrease

noise immunity.

3.7.7 Trace Length and Width

Minimize the parasitic capacitance of the traces and sensor pad. Trace capacitance is minimized when they are short

and narrow.

 The maximum recommended trace length is 12 inches (300 mm) for a standard PCB and 2 inches (50 mm) for

flex circuits.

 Trace width should not be greater than 7 mil (0.18 mm). CapSense traces should be surrounded by hatched

ground with trace-to-ground clearance of 10 mil to 20 mil (0.25 mm to 0.51 mm).

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