Design Considerations
AN64846 - Getting Started with CapSense
®
Doc. No. 001-64846 Rev. *X
79
Equation 3-27. Relationship between minimum PCB length and slider length
𝑃𝐶𝐵 𝑙𝑒𝑛𝑔𝑡ℎ = 𝑆𝑙𝑖𝑑𝑒𝑟 𝐿𝑒𝑛𝑔𝑡ℎ + 3 ∗ 𝑠𝑙𝑖𝑑𝑒𝑟 𝑠𝑒𝑔𝑚𝑒𝑛𝑡 𝑤𝑖𝑑𝑡ℎ + 2 ∗ 𝑎𝑖𝑟 𝑔𝑎𝑝
If the available PCB area is lesser than that required per above equation, you can remove the dummy
segments.
In this case, the minimum PCB length required will be as follows:
𝑃𝐶𝐵 𝑙𝑒𝑛𝑔𝑡ℎ = 𝑆𝑙𝑖𝑑𝑒𝑟 𝐿𝑒𝑛𝑔𝑡ℎ + 𝑠𝑙𝑖𝑑𝑒𝑟 𝑠𝑒𝑔𝑚𝑒𝑛𝑡 𝑤𝑖𝑑𝑡ℎ
Keep in mind the following layout guidelines while designing a slider:
Design the shape of all segments to be as uniform as possible.
Ensure that the length and the width of the traces connecting the segments to the PSoC device are same for all
the segments.
Maintain the same air gap between the sensors or traces to ground plane or hatch fill.
3.8.5.4 Slider Design with LEDs
In some applications it might be required to display finger position by driving LEDs. You can either place the LEDs just
above the slider segments or drill a hole in the middle of a slider segment for LED backlighting, as
When a hole is drilled for placing an LED, the effective area of the slider segment reduces. To achieve an SNR > 5:1,
you need to have a slider segment with a width larger than the LED hole size. Refer to
for minimum slider
width required to achieve an SNR > 5:1 for a given overlay thickness. Follow the guidelines provided in
section for routing the LED traces.
Figure 3-60. Slider Design with LED Backlighting
S
L
D
0
S
L
D
1
S
L
D
2
S
L
D
3
G
N
D
/
S
H
IE
L
D
S
L
D
4
G
N
D
/
S
H
IE
L
D
3.8.6 Sensor and Device Placement
For a CapSense design on 2-Layer and 4-Layer PCBs, follow the below guidelines for sensor and component
placement. If your design requires liquid tolerance, follow the guidelines explained in the
section.
3.8.6.1 2-Layer PCB:
Place the sensors on the top layer of the PCB, as
Place the components and route the sensor traces on the bottom layer of the PCB.
Figure 3-61. CapSense Design on 2-Layer PCB
