TSC2000IPW datasheet(11/34 Pages) TI

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TSC2000

SBAS257

FIGURE 5. Ideal Input Voltages and Output Codes.

FIGURE 6. PENIRQ Functional Block Diagram.

A unique configuration of low on-resistance switches allows

an unselected A/D converter input channel to provide power

and an accompanying pin to provide ground for driving the

touch panel. By maintaining a differential input to the con-

verter and a differential reference input architecture, it is

possible to negate errors caused by the driver switch on-

resistances.

The A/D converter is controlled by an A/D Converter Control

ing upon the bits set in the control register. Channel selec-

tion, scan operation, averaging, resolution, and conversion

rate may all be programmed through this register. These

modes are outlined in the sections below for each type of

analog input. The results of conversions made are stored in

the appropriate result register.

Data Format

The TSC2000 output data is in Straight Binary format, as

shown in Figure 5. This figure shows the ideal output code for

the given input voltage and does not include the effects of

offset, gain, or noise.

Reference

The TSC2000 has an internal voltage reference that can be

set to 1.25V or 2.5V, through the Reference Control Register.

The internal reference voltage is only used in the single-

ended mode for battery monitoring, temperature measure-

ment, 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 VREF pin, and the internal refer-

ence can be turned off.

Variable Resolution

The TSC2000 provides three different resolutions for the A/D

converter: 8-, 10-, or 12-bits. Lower resolutions are often

practical for measurements such as touch pressure. Perform-

ing the conversions at lower resolutions reduces the amount of

time it takes for the A/D converter to complete its conversion

process, which lowers power consumption.

Conversion Clock and Conversion Time

The TSC2000 contains an internal 8MHz 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 A/D converter. The division ratio for

this clock is set in the A/D Converter 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 8MHz clock is used directly, the A/D converter is limited to

8-bit resolution; using higher resolutions at this speed will not

result in accurate conversions. Using a 4MHz conversion

clock is suitable for 10-bit resolution; 12-bit resolution requires

that the conversion clock run at 1MHz or 2MHz.

Regardless of the conversion clock speed, the internal clock

will run nominally at 8MHz. The conversion time of the

TSC2000 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 TSC2000 is used. Throughout

this data sheet, internal and conversion clock cycles will be

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 6. While in the power-down mode, the Y– driver is ON

and connected to GND and the PENIRQ output is connected

to the X+ input. When the panel is touched, the X+ input is

FS = Full-Scale Voltage = V

REF

(1)

1LSB = V

REF

(1)/4096

FS – 1LSB

11...111

11...110

11...101

00...010

00...001

00...000

1LSB

NOTES: (1) Reference voltage at converter: +REF – (–REF). See Figure 4.

(2) Input voltage at converter, after multiplexer: +IN – (–IN). See Figure 4.

Input Voltage(2) (V)

50k

Ω

Y+ or X+ Drivers On,

or TEMP1, TEMP2

Measurements Activated.

Y+

X+

Y–

HIGH Except

when TEMP1,

TEMP2 Activated

PENIRQ

TEMP2

TEMP1

TEMP

DIODE

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