Touch Screen Digitizer

AD7843

Rev. B

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FEATURES

4-wire touch screen interface

Specified throughput rate of 125 kSPS

Low power consumption:

Ratiometric conversion

High speed serial interface

Programmable 8-bit or 12-bit resolution

2 auxiliary analog inputs

Shutdown mode: 1 µA max

16-lead QSOP and TSSOP packages

APPLICATIONS

Personal digital assistants

Smart hand-held devices

Touch screen monitors

Point-of-sales terminals

Pagers

GENERAL DESCRIPTION

The AD7843 is a 12-bit successive approximation ADC with a

synchronous serial interface and low on resistance switches for

driving touch screens. The part operates from a single 2.2 V to

5.25 V power supply and features throughput rates greater than

125 kSPS.

The external reference applied to the AD7843 can be varied

current consumption to less than 1 µA.

The AD7843 features on-board switches. This, coupled with low

power and high speed operation, make this device ideal for

battery-powered systems such as personal digital assistants with

resistive touch screens, and other portable equipment. The part

is available in a 16-lead 0.15" quarter size outline package

(QSOP) and a 16-lead thin shrink small outline package

(TSSOP).

FUNCTIONAL BLOCK DIAGRAM

AD7843

PENIRQ

SPORT

DIN

CS

DOUT

DCLK

BUSY

PEN

INTERRUPT

CHARGE

REDISTRIBUTION

DAC

SAR + ADC

CONTROL LOGIC

4-TO-1

I/P

MUX

T/H

COMP

GND

X+

Y+

X–

Y–

IN3

IN4

Figure 1.

PRODUCT HIGHLIGHTS

1.

Ratiometric conversion mode available eliminating errors

due to on-board switch resistances.

2.

Maximum current consumption of 380 µA while operating

at 125 kSPS.

3.

Power-down options available.

4.

5.

Versatile serial I/O port.