TSC2102IDA datasheet(16/54 Pages) TI

16 / 54 page

TSC2102

SLAS379A− APRIL 2003 − REVISED JUNE 2004

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Data Format

The TSC2102 output data is in unsigned binary format and can be read from the registers over the SPI interface.

Reference

The TSC2102 has an internal voltage reference that can be set to 1.25 V or 2.5 V through the reference control register.

The internal reference voltage must only be used in the single-ended mode for battery monitoring, temperature

measurement, and for utilizing the auxiliary inputs. Optimal touch screen performance is achieved when using a ratiometric

conversion, thus all touch screen measurements are done automatically in the ratiometric mode.

An external reference can also be applied to the VREF pin, and the internal reference can be turned off.

Variable Resolution

The TSC2102 provides three different resolutions for the ADC: 8-, 10- or 12-bits. Lower resolutions are often practical for

measurements such as touch pressure. Performing the conversions at lower resolution reduces the amount of time it takes

for the ADC to complete its conversion process, which lowers power consumption.

Conversion Clock and Conversion Time

The TSC2102 contains an internal 8-MHz clock, which is used to drive the state machines inside the device that perform

the many functions of the part. This clock is divided down to provide a clock to run the ADC. The division ratio for this clock

is set in the ADC control register. The ability to change the conversion clock rate allows the user to choose the optimal value

for resolution, speed, and power. If the 8-MHz clock is used directly, the ADC is limited to 8-bit resolution; using higher

resolutions at this speed does not result in accurate conversions. Using a 4-MHz conversion clock is suitable for 10-bit

resolution; 12-bit resolution requires that the conversion clock run at 1 or 2 MHz.

Regardless of the conversion clock speed, the internal clock runs nominally at 8 MHz. The conversion time of the TSC2102

is dependent upon several functions (see the section Touch Screen Conversion Initiated at Touch Detect in this data sheet).

While the conversion clock speed plays an important role in the time it takes for a conversion to complete, a certain number

of internal clock cycles is needed for proper sampling of the signal. Moreover, additional times, such as the panel voltage

stabilization time, can add significantly to the time it takes to perform a conversion. Conversion time can vary depending

upon the mode in which the TSC2102 is used. Throughout this data sheet, internal and conversion clock cycles are used

to describe the times that many functions take to execute. Considering the total system design, these times must be taken

into account by the user.

When the audio DAC is powered down, the touch screen A/D uses an internal oscillator for conversions. However, to save

power whenever the audio DAC is powered up, the internal oscillator is powered down and MCLK and BCLK are used to

clock the touch screen A/D.

Touch Detect/Data Available

The pen interrupt/data available (PINTDAV) output function is detailed in Figure 13. While in the power-down mode, the

Y– driver is ON and connected to AVSS and the X+ pin is connected through an on-chip pullup resistor to AVDD. In this

mode, the X+ pin is also connected to a digital buffer and mux to drive the PINTDAV output. When the panel is touched,

the X+ input is pulled to ground through the touch screen, and the pen−interrupt signal goes LOW due to the current path

through the panel to AVSS, initiating an interrupt to the processor. During the measurement cycles for X− and Y− position,

the X+ input is disconnected from the pen-interrupt circuit to prevent any leakage current from the pullup resistor flowing

through the touch screen, and thus causing conversion errors.

TSC2102IDA Datasheet(PDF) 16 Page - Texas Instruments