SX8650 Datasheet, PDF (26/56 Pages) Semtech Corporation – World’s Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD

SX8650
World’s Lowest Power & Smallest Footprint 4-wire
Resistive Touchscreen Controller with 15kV ESD
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
4.4. Pen Detection
If the touchscreen is powered between X+ and Y- through a resistor R_PNDT, no current will flow so long as pressure is not
applied to the surface (see Figure 22). Node X+ will remain at the voltage reference voltage. When some pressure is
applied, a current path is created and brings X+ to the level defined by the resistive divider determined by R_PNDT and the
sum of R1, R_T and R4.
The X+ level is detected by a comparator followed by a S-R latch. R_PNDT should be set to a value greater than 7x(Rxtot +
Rytot).
The pen detection will set the PENIRQ bit of the I2C status register and will activate (LOW) the NIRQ pin of the SX8650.
The PENIRQ bit will be cleared and the NIRQ will be de-asserted as soon as the host reads the I2C status register.
+
V_-ref
R_PNDT
Y+
X+
R3
R1
R_T
R4 R2
SQ
RNIRQ
NIRQ
Y-
X-
Figure 22. Pen detection
The resistor R_PNDT can be configured to 4 different values (see Table 9) to accommodate different screen resistive values.
ACS Revision V2.15/October 2009
©2009 Semtech Corp.
Page 25
www.semtech.com