© 2009 Microchip Technology, Inc.

DS41393A-Page 7

7.6

8-wire Touch Sensor Interface

Sensor tail pin-outs can vary by manufacturer and part number. Ensure both sensor tail pins for one sensor axis

(layer) are connected to the controller’s X–/X+ pins and the tail pins for the other sensor axis (layer) are

connected to the controller’s Y–/Y+ pins. The controller’s X–/X+ and Y–/Y+ pin pairs do not need to connect to a

specific sensor axis. The orientation of controller pins X– and X+ to the two sides of a given sensor axis is not

important. Likewise, the orientation of controller pins Y– and Y+ to the two sides of the other sensor axis is not

important.

The 8-wire sensor differs from a 4-wire sensor in that each edge of an 8-wire sensor has a secondary connection

brought to the sensor’s tail. These secondary connections are referred to as “sense” lines. The controller pins

associated with the sense line for an 8-wire sensor contain an ‘S’ prefix in their respective names. For example,

the SY– pin is the sense line connection associated with the main Y– pin connection.

Consult with the sensor manufacturer’s specification to determine which member of each edge connected pair is

the special 8-wire “sense” connection. The controller requires that the main and “sense” tail pin pairs for sensor

edges be connected to controller pin pairs as follows.



Y– and SY–



Y+ and SY+



X– and 5WSX–



X+ and SX+

Connections to a 8-wire touch sensor are as follows.

Figure 6 : 8-wire Touch Sensor Interface

The capacitance of alternate ESD diodes may adversely affect touch performance. A lower

capacitance is better. The PESD5V0S1BA parts shown in the reference design have a typical

capacitance of 35pF. Test to ensure that selected ESD protection does not degrade touch

performance.

ESD protection is shown in the reference design, but acceptable protection is dependent on your

specific application. Ensure your ESD solution meets your design requirements.