WM9715L
Production Data
TOUCHPANEL INTERFACE
The WM9715L includes a touchpanel driver and digitiser circuit for use with 4-wire or 5-wire resistive
touchpanels. The following functions are implemented:
•
•
•
•
•
X co-ordinate measurement
Y co-ordinate measurement
Pen down detection, with programmable sensitivity
Touch pressure measurement (4-wire touchpanel only)
Auxiliary measurement from COMP1/AUX1 (pin 29), COMP2/AUX2 (pin 30),
BMON/AUX3 (pin 31), or WIPER/AUX4 (pin 12)
The touchpanel digitiser uses a very low power, 12-bit successive approximation type ADC. The
same ADC can also be used for battery and auxiliary measurements (see the “Battery Alarm and
Battery Measurement” and “Auxiliary ADC Inputs” sections).
An on-chip switch matrix connects each touchpanel terminal to the supply voltage TPVDD, to ground
(TPGND), or to the ADC input, as required.
RPU
IP
zero power
comparator
PEN
DOWN
SAR
ADC
20K
10K
Figure 5 Touchpanel Switch Matrix
PRINCIPLE OF OPERATION - FOUR-WIRE TOUCHPANEL
Four-wire touchpanels are connected to the WM9715L as follows:
•
•
•
•
Right side contact = X+ (pin 14)
Left side contact = X- (pin 16)
Top side contact = Y+ (pin 15)
Bottom side contact = Y- (pin 17)
PD Rev 4.0 December 2007
38
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
