Touch Screen Controller Data Sheet AD7877 FEATURES FUNCTIONAL BLOCK DIAGRAM V CC 4-wire touch screen interface 7 LCD noise reduction feature (STOPACQ pin) Automatic conversion sequencer and timer AD7877 X+ 12 User-programmable conversion parameters X 10 13 Y+ On-chip temperature sensor: 40C to +85C Y 11 On-chip 2.5 V reference X Y GND X+ Y+ V REF DUAL 3-1 On-chip 8-bit DAC MUX 6 AUX1/GPIO1 AUX2/GPIO2 5 3 auxiliary analog inputs REF REF+ AUX3/GPIO3 4 CLOCK 9 TO 1 IN 12-BIT SUCCESSIVE 1 dedicated and 3 optional GPIOs APPROXIMATION ADC INPUT WITH TRACK-AND-HOLD BAT1 3 MUX BATTERY 2 direct battery measurement channels (0.5 V to 5 V) MONITOR 3 interrupt outputs SEQUENCER STOP ACQ 20 STOPACQ Touch-pressure measurement LOGIC BAT2 2 RESULTS BATTERY REGISTERS Wake up on touch function MONITOR LIMIT Specified throughput rate of 125 kSPS 14 AGND COMPARATOR Single supply, V of 2.7 V to 5.25 V CC LIMIT 15 DGND TEMPERATURE REGISTERS SENSOR Separate VDRIVE level for serial interface 31 V REF ALERT STATUS/ ALERT Shutdown mode: 1 A maximum 22 ALERT MASK REGISTER LOGIC 32-lead, LFCSP, 5 mm 5 mm package 2.5V BUF GPIO REF REGISTERS 21 GPIO4 25-ball,WLCSP, 2.5 mm 2.8 mm package CONTROL AOUT 30 8-BIT DAC TO Qualified for automotive applications REGISTERS DAC REGISTER GPIO1-3 ARNG 29 PEN INTERRUPT CONTROL LOGIC AND SERIAL PORT 17 AND WAKE-UP PENIRQ ON TOUCH APPLICATIONS 18 19 23 26 27 28 Personal digital assistants CS DIN DAV DCLK DOUT V DRIVE Smart hand-held devices Figure 1. Touch screen monitors Point-of-sale terminals Medical devices Cell phones Pagers GENERAL DESCRIPTION The AD7877 is a 12-bit, successive approximation ADC with a To reduce the effects of noise from LCDs, the acquisition phase synchronous serial interface and low on resistance switches for of the on-board ADC is controlled via the STOPACQ pin. User- driving touch screens. The AD7877 operates from a single 2.7 V programmable conversion controls include variable acquisition to 5.25 V power supply (functional operation to 2.2 V), and time and first conversion delay. Up to 16 averages can be taken features throughput rates of 125 kSPS. The AD7877 features per conversion. There is also an on-board DAC for LCD back- direct battery measurement on two inputs, temperature and light or contrast control. The AD7877 runs in either slave or touch-pressure measurement. master mode using a conversion sequencer and timer. It is ideal for battery-powered systems such as personal digital assistants The AD7877 also has an on-board reference of 2.5 V. When not with resistive touch screens and other portable equipment. in use, it can be shut down to conserve power. An external reference can also be applied and varied from 1 V to +VCC, with The part is available in a 32-lead lead frame chip scale package an analog input range of 0 V to VREF. The device includes a (LFCSP), and a 25-ball wafer level chip scale package (WLCSP). shutdown mode that reduces its current consumption to less than 1 A. Rev. E Document Feedback 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. 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Technical Support www.analog.com ADC DATA 03796-001AD7877 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Control Registers ............................................................................ 20 Applications ....................................................................................... 1 Control Register 1 ...................................................................... 20 Functional Block Diagram .............................................................. 1 Control Register 2 ...................................................................... 21 General Description ......................................................................... 1 Sequencer Registers ................................................................... 22 Revision History ............................................................................... 2 Interrupts ..................................................................................... 24 Specifications ..................................................................................... 3 Synchronizing the AD7877 to the Host CPU ......................... 25 Timing Specifications .................................................................. 5 8-Bit DAC ........................................................................................ 26 Timing Diagrams .......................................................................... 5 Serial Interface ................................................................................ 28 Absolute Maximum Ratings ............................................................ 6 Writing Data ............................................................................... 28 ESD Caution .................................................................................. 6 Write Timing ............................................................................... 29 Pin Configurations and Function Descriptions ........................... 7 Reading Data ............................................................................... 29 Typical Performance Characteristics ............................................. 9 V Pin ..................................................................................... 29 DRIVE Terminology .................................................................................... 13 General-Purpose I/O Pins ............................................................. 30 Circuit Information ........................................................................ 14 GPIO Configuration .................................................................. 30 Touch Screen Principles ............................................................ 14 Grounding and Layout .................................................................. 32 Measuring Touch Screen Inputs ............................................... 15 PCB Design Guidelines for Chip Scale Packages ................... 32 Touch-Pressure Measurement .................................................. 16 Register Maps .................................................................................. 33 STOPACQ Pin ............................................................................ 16 Detailed Register Descriptions ..................................................... 35 Temperature Measurement ....................................................... 17 GPIO Registers ........................................................................... 42 Battery Measurement ................................................................. 18 Outline Dimensions ....................................................................... 44 Auxiliary Inputs .......................................................................... 19 Ordering Guide .......................................................................... 45 Limit Comparison ...................................................................... 19 Automotive Products ................................................................. 45 REVISION HISTORY 12/14Rev. D to Rev. E 6/06Rev. A to Rev. B Added Figure 50 Renumbered Sequentially .............................. 44 Added Wafer Level Chip Scale Package .......................... Universal Updated Outline Dimensions ....................................................... 44 Changes to Table 3 ............................................................................. 6 Changes to Ordering Guide .......................................................... 45 Changes to Figure 21 ...................................................................... 11 Change to Figure 25 ....................................................................... 12 12/11Rev. C to Rev. D Changes to Figure 38 and Figure 39 ............................................ 23 Change to Features Section ............................................................. 1 Change to Figure 40 ....................................................................... 24 Updated Outline Dimensions ....................................................... 44 DAV Changes to Data Available Output ( ) Section .................... 24 Changes to Ordering Guide .......................................................... 44 Updated Outline Dimensions ....................................................... 42 Added Automotive Products Section........................................... 44 Changes to Ordering Guide .......................................................... 42 9/09Rev. B to Rev. C 11/04Rev. 0 to Rev. A Changes to Offset Error and Gain Error Parameters .................. 3 Changes to Absolute Maximum Ratings ....................................... 6 Added V to GND Parameter ...................................................... 6 BAT Changes to Figure 4 ........................................................................... 7 Changes to Pin 23 Description ....................................................... 7 Changes to Table 4 ............................................................................. 7 Changes to Power Management (Control Register 2, Changes to Grounding and Layout section ................................ 32 Bits 7:6 ) Section ............................................................................ 22 Changes to Figure 42 ...................................................................... 32 Changes to Bit 7 Description (Table 17) ...................................... 36 Changes to Ordering Guide .......................................................... 43 Updated Outline Dimensions ....................................................... 44 Changes Ordering Guide ............................................................... 44 7/04Revision 0: Initial Version Rev. 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