WM9713 datasheet(62/111 Pages) WOLFSON

62 / 111 page

WM9713L

Preliminary Technical Data

PTD, March 2004, Rev 2.2

Figure 21 X Co-ordinate Measurement on 5-wire Touchpanel

For an X co-ordinate measurement, the top left and bottom left corners of the touchpanel are

grounded internally to the WM9713L, while the top right and bottom right contacts are connected to

TPVDD. The bottom plate becomes a potential divider with a voltage gradient in the X direction. The

voltage at the point of contact is proportional to its X co-ordinate. This voltage is measured on the

WIPER pin and converted to a digital value by the ADC.

Due to the ratiometric measurement method, the supply voltage does not affect measurement

accuracy. The voltage references VREF+ and VREF- are taken from after the matrix switches, so

that any voltage drop in these switches has no effect on the ADC measurement.

Figure 22 Y Co-ordinate Measurement on 5-wire Touchpanel

Y co-ordinate measurements are similar to Y co-ordinate measurements. However, the voltage

gradient on the bottom plate is in the Y direction instead of the X direction. This is achieved by

grounding the bottom left and bottom right corners of the touchpanel, and connecting the top left and

top right contacts to TPVDD.

WM9713 Datasheet(PDF) 62 Page - Wolfson Microelectronics plc