AD7877_15 datasheet, PDF - EEWORLD Datasheet

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AD7877_15: DescriptionTouch Screen Controller; File Size830KB，45 Pages; ManufacturerADI; Websitehttps://www.analog.com

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AD7877_15 Overview

Touch Screen Controller

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Data Sheet

FEATURES

4-wire touch screen interface

LCD noise reduction feature (STOPACQ pin)

Automatic conversion sequencer and timer

User-programmable conversion parameters

On-chip temperature sensor: −40°C to +85°C

On-chip 2.5 V reference

On-chip 8-bit DAC

3 auxiliary analog inputs

1 dedicated and 3 optional GPIOs

2 direct battery measurement channels (0.5 V to 5 V)

3 interrupt outputs

Touch-pressure measurement

Wake up on touch function

Specified throughput rate of 125 kSPS

Single supply, V

of 2.7 V to 5.25 V

Separate V

DRIVE

level for serial interface

Shutdown mode: 1 µA maximum

32-lead, LFCSP, 5 mm × 5 mm package

25-ball,WLCSP, 2.5 mm × 2.8 mm package

Qualified for automotive applications

Touch Screen Controller

AD7877

FUNCTIONAL BLOCK DIAGRAM

X+

X–

Y+

Y–

AD7877

X– Y– GND X+ Y+ V

REF

AUX1/GPIO1

AUX2/GPIO2

AUX3/GPIO3

BAT1

BATTERY

MONITOR

9 TO 1

INPUT

MUX

DUAL 3-1

MUX

REF–

REF+

CLOCK

12-BIT SUCCESSIVE

APPROXIMATION ADC

WITH TRACK-AND-HOLD

ADC DATA

SEQUENCER

STOP

ACQ

LOGIC

STOPACQ

BAT2

BATTERY

MONITOR

RESULTS

REGISTERS

LIMIT

COMPARATOR

AGND

TEMPERATURE

SENSOR

REF 31

LIMIT

REGISTERS

DGND

ALERT STATUS/

MASK REGISTER

2.5V

REF

AOUT

ARNG

BUF

GPIO

REGISTERS

CONTROL

REGISTERS

ALERT

LOGIC

ALERT

GPIO4

8-BIT

DAC

GPIO1-3

PENIRQ

APPLICATIONS

Personal digital assistants

Smart hand-held devices

Touch screen monitors

Point-of-sale terminals

Medical devices

Cell phones

Pagers

CONTROL LOGIC AND SERIAL PORT

PEN INTERRUPT

AND WAKE-UP

ON TOUCH

DIN

DAV

DCLK

DOUT

DRIVE

Figure 1.

GENERAL DESCRIPTION

The AD7877 is a 12-bit, successive approximation ADC with a

synchronous serial interface and low on resistance switches for

driving touch screens. The AD7877 operates from a single 2.7 V

to 5.25 V power supply (functional operation to 2.2 V), and

features throughput rates of 125 kSPS. The AD7877 features

direct battery measurement on two inputs, temperature and

touch-pressure measurement.

The AD7877 also has an on-board reference of 2.5 V. When not

in use, it can be shut down to conserve power. An external

reference can also be applied and varied from 1 V to +V

, with

an analog input range of 0 V to V

REF

. The device includes a

shutdown mode that reduces its current consumption to less

than 1 µA.

Rev. D

Information furnished by Analog Devices is believed to be accurate and reliable. However, no

responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other

rights of third parties that may result from its use. Specifications subject to change without notice. No

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

Trademarks and registered trademarks are the property of their respective owners.

To reduce the effects of noise from LCDs, the acquisition phase

of the on-board ADC is controlled via the STOPACQ pin. User-

programmable conversion controls include variable acquisition

time and first conversion delay. Up to 16 averages can be taken

per conversion. There is also an on-board DAC for LCD back-

light or contrast control. The AD7877 runs in either slave or

master mode using a conversion sequencer and timer. It is ideal

for battery-powered systems such as personal digital assistants

with resistive touch screens and other portable equipment.

The part is available in a 32-lead lead frame chip scale package

(LFCSP), and a 25-ball wafer level chip scale package (WLCSP).

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781.329.4700

www.analog.com

03796-001

AD7877

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1

Functional Block Diagram .............................................................. 1

General Description ......................................................................... 1

Revision History ............................................................................... 2

Specifications..................................................................................... 3

Timing Specifications .................................................................. 5

Timing Diagrams.......................................................................... 5

Absolute Maximum Ratings............................................................ 6

ESD Caution .................................................................................. 6

Pin Configurations and Function Descriptions ........................... 7

Typical Performance Characteristics ............................................. 9

Terminology .................................................................................... 13

Circuit Information ........................................................................ 14

Touch Screen Principles ............................................................ 14

Measuring Touch Screen Inputs ............................................... 15

Touch-Pressure Measurement .................................................. 16

STOPACQ Pin ............................................................................ 16

Temperature Measurement ....................................................... 17

Battery Measurement ................................................................. 18

Auxiliary Inputs .......................................................................... 19

Limit Comparison ...................................................................... 19

Data Sheet

Control Registers ............................................................................ 20

Control Register 1 ...................................................................... 20

Control Register 2 ...................................................................... 21

Sequencer Registers ................................................................... 22

Interrupts ..................................................................................... 24

Syncronizing the AD7877 to the Host CPU ........................... 25

8-Bit DAC ........................................................................................ 26

Serial Interface ................................................................................ 28

Writing Data ............................................................................... 28

Write Timing ............................................................................... 29

Reading Data ............................................................................... 29

DRIVE

Pin ..................................................................................... 29

General-Purpose I/O Pins ............................................................. 30

GPIO Configuration .................................................................. 30

Grounding and Layout .................................................................. 32

PCB Design Guidelines for Chip Scale Packages ................... 32

Detailed Register Descriptions ..................................................... 35

GPIO Registers ........................................................................... 42

Outline Dimensions ....................................................................... 44

Ordering Guide .......................................................................... 44

Automotive Products ................................................................. 44

Changes to Figure 21...................................................................... 11

Change to Figure 25 ....................................................................... 12

Changes to Figure 38 and Figure 39............................................. 23

Change to Figure 40 ....................................................................... 24

Changes to Data Available Output (DAV) Section .................... 24

Updated Outline Dimensions ....................................................... 42

Changes to Ordering Guide .......................................................... 42

11/04—Rev. 0 to Rev. A

Changes to Absolute Maximum Ratings .......................................6

Changes to Figure 4 ...........................................................................7

Changes to Table 4.............................................................................7

Changes to Grounding and Layout section ................................ 32

Changes to Figure 42...................................................................... 32

Changes to Ordering Guide .......................................................... 43

7/04—Revision 0: Initial Version

REVISION HISTORY

12/11—Rev. C to Rev. D

Change to Features Section ............................................................. 1

Updated Outline Dimensions ....................................................... 44

Changes to Ordering Guide .......................................................... 44

Added Automotive Products Section .......................................... 44

9/09—Rev. B to Rev. C

Changes to Offset Error and Gain Error Parameters .................. 3

Added V

BAT

to GND Parameter ...................................................... 6

Changes to Pin 23 Description ....................................................... 7

Changes to Power Management (Control Register 2,

Bits[7:6]) Section ............................................................................ 22

Changes to Bit 7 Description (Table 17) ...................................... 36

Updated Outline Dimensions ....................................................... 44

Changes Ordering Guide ............................................................... 44

6/06—Rev. A to Rev. B

Added Wafer Level Chip Scale Package........................... Universal

Changes to Table 3 ............................................................................ 6

Rev. D | Page 2 of 44

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