SX8650

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Page 13

ADVANCED COMMUNICATIONS & SENSING

DATASHEET

World’s Lowest Power & Smallest Footprint 4-wire

Resistive Touchscreen Controller with 15kV ESD

Revision V2.19/October 2010

©2010 Semtech Corp.

3. Functional Description

3.1. General Introduction

This section provides an overview of the SX8650 architecture, device pinout and a typical application.

The SX8650 is designed for 4-wire resistive touch screen applications (Figure 6).The touch screen or touch panel is the

resistive sensor and can be activated by either a finger or stylus. The touch screen coordinates and touch pressure are

converted into I2C format by the SX8650 for transfer to the host.

Figure 6. SX8650 with screen

3.2. Channel Pins

3.2.1. X+, X-, Y+. Y-

The SX8650's channel pins (X+, X-, Y+, Y-) directly

connect to standard touch screen X and Y resistive

layers. The SX8650 separately biases each of these

layers and converts the resistive values into (X,Y)

coordinates.

The channel pins are protected to VDD and GROUND.

Figure 7 shows the simplified diagram of the X+, X-, Y+,

Y- pins.

Figure 7. Simplified diagram of X+, X-, Y+, Y- pins

3.2.2. AUX

The SX8650 interface includes an AUX pin that serves

two functions: an ADC input; and a start of conversion

trigger. When used as an ADC, the single ended input

range is from GND to VDD, referred to GND. When

the AUX input is configured to start conversions, the

AUX input can be further configured as a rising and /

or falling edge trigger.

The AUX is protected to VDD and GROUND.

Figure 8 shows a simplified diagram of the AUX pin.

Figure 8. Simplified diagram of AUX

Touch

Screen

Interface

SX8650

VDD

AUX

X+

Y+

X-

Y-

A0

NIRQ

NRST

SCL

SDA

GND

HOST

Control

I2C

Digital

Filter

ref+

ref-

ADC

in

out

OSC

POR

Vref

VDD_HOST

VDD

X+

X-

Y+

Y-

Touch Screen

Interface

AUX

ADC

Control

VDD