TSC2100 datasheet(21/71 Pages) TI

21 / 71 page

TSC2100

SLAS378− NOVEMBER 2003

www.ti.com

Touch Screen Measurements

The touch screen ADC can be controlled by the host processor or can be self−controlled to offload processing from the

host processor. Bit D15 of REG00H/Page1 sets the control mode of the TSC2100 touch screen ADC.

Conversion Controlled by TSC2100 Initiated at Touch Detect

In this mode, the TSC2100 detects when the touch panel is touched and causes the PINTDAV line to go low. At the same

time, the TSC2100 starts up its internal clock. Assuming the part was configured to convert XY coordinates, it then turns

on the Y drivers, and after a programmed panel voltage stabilization time, powers up the ADC and converts the Y

coordinate. If averaging is selected, several conversions may take place; when data averaging is complete, the Y

coordinate result is stored in the Y register.

If the screen is still touched at this time, the X drivers are enabled, and the process repeats, but measuring instead the X

coordinate, storing the result in the X register.

If only X and Y coordinates are to be measured, then the conversion process is complete. The time it takes to complete

this process depends upon the selected resolution, internal conversion clock rate, averaging selected, panel voltage

stabilization time, and precharge and sense times.

If the pressure of the touch is also to be measured, the process continues in the same way, measuring the Z1 and Z2 values,

and placing them in the Z1 and Z2 registers. As before, this process time depends upon the settings described above.

See the section Conversion Time Calculation for the TSC2100 in this data sheet for timing diagrams and conversion time

calculations.

Conversion Controlled by TSC2100 Initiated by the Host

In this mode, the TSC2100 detects when the touch panel is touched and causes the pen-interrupt signal line to go low. The

host recognizes the interrupt request, and then writes to the ADC control register (D13−D10 REG00H/Page1) to select one

of the touch screen scan functions. The host can either choose to initiate one of the scan functions, in which case the

TSC2100 controls the driver turnons, and wait times (e.g. upon receiving the interrupt the host can initiate the continuous

scan function X−Y−Z1−Z2 after which the TSC2100 controls the rest of conversion). The host can also choose to control

each aspect of conversion by controlling the driver turnons and start of conversions. For example, upon receiving the

interrupt request, the host turns on the X drivers. After waiting for the settling time, the host then addresses the TSC2100

again, this time requesting an X coordinate conversion, and so on.

The main difference between this mode and the previous mode is that the host, not the TSC2100, controls the touch screen

scan functions.

See the section Conversion Time Calculation for the TSC2100 in this data sheet for timing diagrams and conversion time

calculations.

Temperature Measurement

In some applications, such as battery recharging, a measurement of ambient temperature is required. The temperature

measurement technique used in the TSC2100 relies on the characteristics of a semiconductor junction operating at a fixed

current level. The forward diode voltage (VBE) has a well-defined characteristic versus temperature. The ambient

temperature can be predicted in applications by knowing the 25

°C value of the VBE voltage and then monitoring the delta

of that voltage as the temperature changes.

TSC2100 Datasheet(PDF) 21 Page - Texas Instruments