wm9713 Wolfson Microelectronics plc, wm9713 Datasheet - Page 68

• Manufacturer Part Number: wm9713
• Description: Ac?97 Audio + Touchpanel Codec
• Manufacturer: Wolfson Microelectronics plc

WM9713L
PRINCIPLE OF OPERATION - FIVE-WIRE TOUCHPANEL
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Five-wire touchpanels are connected to the WM9713L as follows:
Top sheet contact = WIPER/AUX4 (pin 12)
Top left corner of bottom sheet = TL (pin 16)
Top right corner of bottom sheet = TR (pin 15)
Bottom left corner of bottom sheet = BL (pin 17)
Bottom right corner of bottom sheet = BR (pin 14)
Figure 29 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 30 Y Co-ordinate Measurement on 5-wire Touchpanel
PP Rev 3.2 September 2008
Pre-Production
68