TSC2301 datasheet(21/92 Pages) TI

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TSC2301

SLAS371D – SEPTEMBER 2002 – REVISED AUGUST 2004

Reference

The TSC2301 has an internal voltage reference that can be set to 1.2 V or 2.5 V, through the reference control

remain on to reduce settling time.

The internal reference voltage is only 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 differential mode.

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

Variable Resolution

The TSC2301 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 TSC2301 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 generate the actual ADC conversion clock.

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

TSC2301 is dependent upon several functions. 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 TSC2301 is used. Throughout this data sheet, internal and conversion clock cycles are used to

describe the times that many functions take. In considering the total system design, these times must be taken

into account by the user.

Touch Detect

The pen interrupt (PENIRQ) output function is detailed in Figure 49. While in the touch screen monitoring mode,

the Y- driver is ON and connected to GND, the X+ input is connected through a pullup resistor to VDD, and the

PENIRQ output reflects the state of the X+ input. When the panel is touched, the X+ input is pulled to ground

through the touch screen and PENIRQ output goes LOW due to the current path through the panel to GND,

initiating an interrupt to the processor. During the measurement cycles for X- and Y-position, the X+ input is

disconnected from PENIRQ to eliminate any leakage current from the pullup resistor that might flow through the

touch screen, thus causing no errors.

TSC2301 Datasheet(PDF) 21 Page - Texas Instruments