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High Except

When TEMP1,

TEMP2 Activated

Internal

50 k

PENIRQ

TEMP1 TEMP2

TEMP DIODE

Y+ or X+ Drivers on,

or TEMP1, TEMP2

Measurements Activated

Y+

X+

Y–

TSC2301

SLAS371D – SEPTEMBER 2002 – REVISED AUGUST 2004

Figure 49. PENIRQ Functional Block Diagram

In modes where the TSC2301 needs to detect if the screen is still touched (for example, when doing a

PENIRQ-initiated X, Y, and Z conversion), the TSC2301 must reconnect the drivers so that the 50-k Ω resistor is

connected again. Because of the high value of this pullup resistor, any capacitance on the touch screen inputs

cause a long delay time, and may prevent the detection from occurring correctly. To prevent this, the TSC2301

has a circuit which allows any screen capacitance to be precharged through a low-resistance connection to VDD,

so that the pullup resistor doesn't 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

control register. All other drivers (X-,Y+, Y-) are off during precharging.

This does point out, however, the need to use the minimum capacitor values possible on the touch screen inputs.

These capacitors may be needed to reduce noise, but too large a value increases the needed precharge and

sense times, as well as panel voltage stabilization time.

In self-controlled modes where the TSC2301 automatically performs conversions when it detects a pen touch, it

is generally not necessary for the host processor to monitor PENIRQ. Instead, the host must monitor DAV, which

goes low when data is available in the appropriate data register, and returns high when all new data has been

read back by the host.