ANALOG-TO-DIGITAL CONVERTER

Converter

-REF

+REF

+IN

-IN

PenTouch

Control

Logic

A[2:0]

MedianValueFilter

and

AveragingFilter

(MAV)

V

DD

GND

GND

R

IRQ

90kW

50kW

AUX

GND

X+

X-

Y+

Y-

VDD/REF

PENIRQ

Reference

TSC2008

Figure 24 shows the analog inputs of the TSC2008. The analog inputs (X, Y, and Z touch panel coordinates, chip

temperature and auxiliary inputs) are provided via a multiplexer to the Successive Approximation Register (SAR)

analog-to-digital converter (ADC). The A/D architecture is based on capacitive redistribution architecture, which

inherently includes a sample-and-hold function.

Figure 24. Analog Input Section (Simplified 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 converter and a differential reference input architecture, it is possible to negate errors

caused by the driver switch on-resistance.

The TSC2008 uses an external voltage reference applied to the VDD/REF pin. The upper reference voltage

range is the same as the supply voltage range, which allows for simple, 1.2V to 3.6V single-supply operation of

the chip.

Copyright © 2008, Texas Instruments Incorporated

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Product Folder Link(s): TSC2008