TSC2004 datasheet(20/62 Pages) TI2

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Touch Detect

SNSGND

SNSVDD

PenTouch

X+

Y+

Y-

HighwhentheX+orY+

driverison,orwhenany

sensorconnection/short

circuittestsareactivated.

AGND

Sense

Viasgotosystemanaloggroundplane.

DGND

Highwhen

theX+orY+

driverison.

Control

Logic

DataAvailable

Level

Shifter

50k

IRQ

(1)

SNSVDD

PINTDAV

AnalogVDD

Plane

TSC2004

SBAS408E – JUNE 2007 – REVISED MARCH 2008

PINTDAV can be programmed to generate an interrupt to the host. Figure 30 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.

(1)

Untrimmed resistor; see the typical value in the Electrical Characteristics

Figure 30. Example of a Pen-Touch Induced Interrupt via the PINTDAV Pin

In modes where the TSC2004 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 TSC2004 must reset the drivers so that the RIRQ resistor

is connected again. Because of the high value of this pull-up resistor, any capacitance on the touch screen inputs

causes a long delay time, and may prevent the detection from occurring correctly. To prevent this possible delay,

the TSC2004 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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