Cypress CapSense CY8C20x36 Guía de usuario descargar pdf (Pagina 54)

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

Another approach to reducing crosstalk is to slow down the rising and falling edges of the LED drive voltage using a

filter capacitor. Figure 3-34 shows an example circuit of this solution. The value of the added capacitor depends on

the drive current requirements of the LED; however, a value of 0.1 µF is typical.

Figure 3-34. Filter Capacitor Solution for Crosstalk

VDD

LED

CapSense

Sensor

Capacitor

Series

resistor

CapSense

Controller

LED

Port Pin

Sensor

Port Pin

3.7.10 Vias

Use the minimum number of vias to route CapSense inputs to minimize parasitic capacitance. The vias should be

placed to minimize the trace length, which is usually on the edge of the sensor pad, as shown in Figure 3-35.

Figure 3-35. Vias Placement on Sensor Pad

3.7.11 Ground Plane

Ground fill is added to both the top and bottom of the sensing board. When ground fill is added near a CapSense

sensor pad, there is a tradeoff between maintaining a high level of CapSense signal and increasing the noise

immunity of the system. Typical hatching for the ground fill is 25 percent on the top layer (7 mil line, 45 mil spacing)

and 17 percent on the bottom layer (7 mil line, 70 mil spacing).

Figure 3-36. Recommended Button and Slider Layout Top Layer

1 2 ... 49 50 51 52 53 54 55 56 57 58 59 ... 74 75

Sin comentarios

Cypress CapSense CY8C20x36 Guía de usuario Pagina 54