NT1080 Datasheet, PDF (7/22 Pages) List of Unclassifed Manufacturers – 8-bit Microcontroller

NT1080
4 CAPACITIVE TOUCH KEY
4.1 Input Circuit
Each capacitive touch key needs to connected with one resistor as shown in Figure 4-1. It is
strongly recommended that the resistor value is 100 kΩ. At the same time, all the resistors need to
be kept as close to sensor pad as possible during PCB layout.
Touch
Pad
100K
SENn
Figure 4-1 Touch Key Reference Circuit
4.2 Sensor Pad and Ground for PCB Layout
The size of sensor pad, using circular shape with diameter equal or greater than 8mm is
recommended. Actually, sensor pad could be any kinds of shape, but fulfilling finger size is suitable.
Extra ground-net around sensor pads is not needed for PCB artwork. However, ground-net along
sensor pad to chip is alternative. Figure 4-2 shows that the PCB line width of sensor pad to chip
should be 0.254mm (10mil) or less and to keep distance with ground at least 1mm. The other layer
of PCB could implement ground-net for PCB artwork to block noise interfering with signal line. All
the subsidiary components need to be kept as close to sensor pad as possible at PCB layout.
Meanwhile, touch key chip (NT1080) and touch pad located in the PCB board would be better.
0.254mm(10mil)
Sensor
Pad
GND
GND
>1mm
>1mm
Figure 4-2 Sensor Pad and Ground-Net
As shown in Figure 4-3, a spring attached with metal-panel can be used to act as sensor pads. It is
recommended that metal-panel (ring) should be adhered to the inside of cover to be an effective
sensing area. If user wants to add a LED in the middle of sensor pad, the measure of sensor area
should be increased to compensate the hollowing part and keeping the same sensitivity.
Oct 26, 2015
Page 7 of 22
Rev 1.0