Datasheet

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Touch Detect
SNSGND
TEMP1 TEMP2
SNSVDD
PenTouch
X+
Y+
Y-
HighwhentheX+orY+
driverison,orwhenany
sensorconnection/short
circuittestsareactivated.
AGND
ON
Sense
Viasgotosystemanaloggroundplane.
DGND
Highwhen
theX+orY+
driverison.
Control
Logic
DataAvailable
Level
Shifter
R
50k
IRQ
W
SNSVDD
PINTDAV
AnalogVDD
Plane
TSC2005
SBAS379C – DECEMBER 2006 – REVISED MARCH 2008
PINTDAV can be programmed to generate an interrupt to the host. Figure 26 details an example for the
Y-position measurement. While in the power-down mode, the Y – driver is on and connected to GND. The internal
pen-touch signal depends on whether or not the X+ input is driven low. When the panel is touched, the X+ input
is pulled to ground through the touch screen and the internal pen-touch output is set to low because of the
detection on the current path through the panel to GND, which initiates an interrupt to the processor. During the
measurement cycles for X- and Y-Position, the X+ input is disconnected, which eliminates any leakage current
from the pull-up resistor to flow through the touch screen, thus causing no errors.
Figure 26. Example of a Pen-Touch Induced Interrupt via the PINTDAV Pin
In modes where the TSC2005 must detect whether or not the screen is still being touched (for example, when
doing a pen-touch initiated X, Y, and Z conversion), the TSC2005 must reset the drivers so that the R
IRQ
resistor
is connected again. Because of the high value of this pull-up resistor, any capacitance on the touch screen inputs
will cause a long delay time, and may prevent the detection from occurring correctly. To prevent this possible
delay, the TSC2005 has a circuit that allows any screen capacitance to be precharged, so that the pull-up
resistor does not have to be the only source for the charging current. The time allowed for this precharge, as well
as the time needed to sense if the screen is still touched, can be set in the configuration register.
This configuration underscores the need to use the minimum possible capacitor values on the touch screen
inputs. These capacitors may be needed to reduce noise, but too large a value will increase the needed
precharge and sense times, as well as the panel voltage stabilization time.
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