Touch Screen Controller

APT7843 Touch Screen Controller Description The APT7843 Touch Screen Controller IC provides all the screen drive , A/D converter and control circuits to easily interface to 4 wire resistive touch screen. The IC continually monitors the screen waiting for a touch. When the screen touched , the IC performs A/D converter to determine the location of touch. Also , this device has 2 auxiliary input to A/D converter , allowing for the measurement of other inputs such as battery voltage. Features • • • • • • • 16 pin SSOP or TSSOP Operates with four wire touch screen 8-bit or 12 bit A/D converter Ratiometric Conversion eliminates screen calibration 2 auxiliary analog inputs 4 wire serial interface Full power down control Applications • • • www.DataSheet4U.com PDAs Handheld computer Touch-screen kiosks Pin Assignment +Vcc X+ Y+ XYGND IN3 IN4 1 2 3 4 5 6 7 8 16 15 14 13 12 DCLK CS DIN BUSY DOUT 11 PENIRQ 10 9 +Vcc VREF Order Information APT7843 Temp. Range Package Code Package Code N : SSOP Temp. Range I : - 40 to 85 ° C O : TSSOP ANPEC reserves the right to make changes to improve reliability or manufacturability without notice, and advise customers to obtain the latest version of relevant information to verify before placing orders. Copyright  ANPEC Electronics Corp. Rev. A.8 - Apr., 2002 1 www.anpec.com.tw APT7843 Block Diagram PENIRQ X+ XScreen Driver DCLK CS MUX 12 Bit or 8 Bit A/D Converter Serial Interface Y+ YIN3 IN4 VREF DIN DOUT BUSY Pin Descriptions PIN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 NAME +Vcc X+ Y+ XYGND IN3 IN4 VREF DESCRIPTION Power Supply,2.2V to 5V. Connect to X+ on touch screen. Connect to Y+ on touch screen. Connect to X- on touch screen. Connect to Y- on touch screen. Ground Auxiliary Input of A/D converter. Auxiliary input of A/D converter. Voltage Reference Input. +Vcc Power Supply,2.2V to 5V. PENIRQ Pen interrupt. Open anode output (requires 10kΩ to 100kΩ pull-up resistor externally) DOUT Serial Data Output. This output is high impedance when CS is HIGH. BUSY Busy Output. This output is high impedance when CS is HIGH. DIN Serial Data input. CS DCLK Chip Select. (Active Low) Serial Clock. Copyright  ANPEC Electronics Corp. Rev. A.8 - Apr., 2002 2 www.anpec.com.tw APT7843 Electrical Characteristics At TA = -40°C to 85°C , VCC = +2.7V , VREF = +2.5V , fSAMPLE = 125kHz , fCLK = 16 • f SAMPLE = 2MHz , 12-bit mode , and digital inputs = GND or Vcc , unless otherwise noted. PA R A M E T E R DC ACCURACY R esolu tio n N o m issing co de Integra l N onlin earity O ffset E rror O ffset E rror M atch G ain E rror G ain E rror M atch N oise P ow er S u pply R ejectio n R E F E R A N C E IN P U T V R E F In put Voltage R an ge D C Le akage C urrent V R E F In put Im p eda nce V R E F In put C urrent F S A M P LE = 12 .5 kH z C S = V cc D Y N A M IC P E R F O R E N C E A perture D e lay A perture Jitter C han nel to C han ne l Isolation C O N V E R S IO N R AT E C onversion Tim e Track/H old A cquis ition Tim e T hrough put R ate S W IT C H D R IV E R S O n-R esistance Y+ , X+ Y- , XL O G IC O U T P U T S O utput H ig h Vo lta ge , V O H O utput Low Voltage , V O L PEN IR Q output low voltage , V O L Floating-S tate Leakage C urrent Floating-State Output Capacitance O utput C oding |I O H | ≤ -250µ A |I O L | ≤ 250µ A V cc–0.2 0.4 0.2 ± 10 10 S traight ( N atura l ) B in ary V V V µA pF 4 4 15 15 Ω Ω 3 125 12 DCLK cycles DCLK cycles KSPS V IN = 2.5 V p-p ; F IN = 5 0kH z 30 100 100 ns ps dB C S = G N D or V cc 1.0 ± 1 5 13 2.5 3 40 V cc µA GΩ µA µA µA 0.1 30 70 0.1 11 ± 2 ± 6 1 ± 4 1 12 B its B its LS B LS B LS B LS B LS B uV rm s dB C O N D IT IO N S A P T 78 43 M IN TYP MAX U N IT S Note : (1) LSB means least Significant Bit. With VREF equal to +2.5V , one LSB is 610µV Copyright  ANPEC Electronics Corp. Rev. A.8 - Apr., 2002 3 www.anpec.com.tw APT7843 Electrical Characteristics (Cont.) PA R A M E T E R L O G IC IN P U T S In p u t H ig h Vo lta g e , V INH In p u t L o w Vo lta g e , V INL Inp ut C urre nt , IIN In p u t C a p a c ita n c e , C IN A N ALO G IN P U T In p u t Vo lta g e R a n g e s D C Le aka ge C u rre nt In p u t C a p a c ita n c e P O W E R R EQ U IR E M EN T S Vcc Ic c N orm a l M o d e (S ta tic ) N orm al M od e (F S A M P L E = 1 2 .5k S P S ) S hutdow n M o d e (S ta tic) Showdown D ig ita l I/P s = 0 V o r V cc V cc = 3.6V V cc = 3.6V 650 540 3 V cc = 3.6V 3.6 µA µA µA µW 2.7 3.6 V C O N D IT IO N S APT7843 M IN 2.4 0.8 ± 1 10 0 ± 0.1 30 V REF TYP MAX U N IT S | I I N H | ≤ + 5 µA | I I N L | ≤ + 5 µA V V µA pF Vo lts µA pF Copyright  ANPEC Electronics Corp. Rev. A.8 - Apr., 2002 4 www.anpec.com.tw APT7843 Electrical Characteristics At TA = -40°C to 85°C, VCC = +2.4V , VREF don’t care, fSAMPLE = 1.25KHz, fCLK = 16 • f SAMPLE = 20KHz, 8-bit differential mode, no support single end mode, and digital inputs = GND or Vcc , unless otherwise noted. PARAMETER DC ACCURACY Resolution No missing code Integral Nonlinearity Offset Error Offset Error Match Gain Error Gain Error Match Noise Power Supply Rejection DYNAMIC PERFORENCE Aperture Delay Aperture Jitter Channel to Channel Isolation CONVERSION RATE Conversion Time Track/Hold Acquisition Time Throughput Rate SWITCH DRIVERS On-Resistance Y+ , X+ Y- , XLOGIC OUTPUTS Output High Voltage , VOH Output Low Voltage , VOL PENIRQ output low voltage , VOL Floating-State Leakage Current Floating-State Output Capacitance Output Coding CONDITIONS APT7843 MIN TYP 8 7 ±2 ±6 0.1 0.1 30 70 30 100 1 ±4 1 MAX UNITS Bits Bits LSB LSB LSB LSB LSB uV rms dB ns ps dB 12 DCLK cycles DCLK cycles 1.25 KSPS VIN = 2.5Vp-p ; FIN = 50kHz 100 3 4 4 |IOH| ≤ -250µA |IOL| ≤ 250µA Vcc–0.2 0.4 0.2 ± 10 10 Straight ( Natural ) Binary Ω Ω V V V µA pF Copyright  ANPEC Electronics Corp. Rev. A.8 - Apr., 2002 5 www.anpec.com.tw APT7843 Electrical Characteristics (Cont.) PA R A M E T E R L O G IC IN P U T S In p u t H ig h Vo lta g e , V IN H In p u t L o w Vo lta g e , V INL In p u t C urr e n t , IIN In p u t C a p a c it a n c e , C IN A NALOG IN PUT In p u t Vo lt a g e R a n g e s D C Leakage C urrent In p u t C a p ac ita n c e P O W E R R E Q U IR E M E N T S Vcc Ic c N orm a l M o d e (S ta tic ) N orm a l M o de (F S A M P L E = 1 2.5k S P S ) S h u td o w n M o d e (S ta tic) Showdown D ig ita l I/P s =0 V o r V cc V cc = 2.4V V cc = 2.4V V cc = 2.4V 280 650 540 3 3.6 µA µA µA µW 2.2 2.4 3.6 V 0 ± 0 .1 30 V REF Vo lts µA pF | I I N H | ≤ + 5 µA | I I N L | ≤ + 5 µA 2.2 VDD+0.2 0.6 ± 1 10 V V µA pF C O N D IT IO N S APT7843 M IN TYP MAX U N IT S Copyright  ANPEC Electronics Corp. Rev. A.8 - Apr., 2002 6 www.anpec.com.tw APT7843 Chip Overview The APT7843 is a successive approximation analogto-digital (A/D) converter based around a capacitive redistribution DAC. Figure 1 show basic operation of the APT7843. The APT7843 communicates via a 4-wire serial interface. The device also requires an external reference voltage Vref. The value of the reference voltage directly sets the input range of the converter. The APT7843 primary function is to control resistive touchscreens. When a touch is detected , pen interrupt pin will go low to wake up extenal microprocess. The microprocessor writes register to initiate conversion. This A/D converter may also be used to measure voltage presented on the IN3 , IN4 pins. Analog Input The analog input to the converter is provided via a four-channel multiplexer. Figure 2 shows a simplified diagram of the APT7843 with the difference input of the A/D converter , and the converter’s reference. Table I and Table II also show the relationship between the A2 , A1 , A0 , SER/ DFR and the configuration of the APT7843. See the section of single-ended reference mode and differential reference mode for more details. +2 .2 V to +5 V 1u F to 10 uF (O ptio nal) 0.1u F 1 A P T 784 3 +V c c X+ Y+ XYGND IN 3 IN 4 DCLK CS D IN BUSY DOUT P E N IR Q +V c c V RE F 16 15 14 13 12 11 10 9 2 3 4 5 6 7 To T o uch S c ree n C on nec t to M icropros sor A u xiliary Inpu t 8 10 0k oh m (op tion al) 0.1u F FIGURE 1. Basic Operation of the APT7843 Copyright  ANPEC Electronics Corp. Rev. A.8 - Apr., 2002 7 www.anpec.com.tw APT7843 PENIRQ +Vcc VREF A2-A0 (Shown 001 B) SER/DFR (Shown HIGH) X+ X- Y+ Y- +IN -IN +REF CONVERTER -REF IN3 IN4 GND FIGURE 2. Simplified Diagram of Analog Input A2 0 1 0 1 A1 0 0 1 1 A0 1 1 0 0 X+ +IN Y+ +IN IN3 IN4 +IN +IN -IN GND GND GND GND X SWITCHES Y SWITCHES OFF ON ON OFF OFF OFF OFF OFF +REF +VREF +VREF +VREF +VREF -REF GND GND GND GND TABLE I. Input C onfiguration, Single-Ended Reference Mode (SER/ DFR HIGH). A2 0 1 0 1 A1 0 0 1 1 A0 1 1 0 0 X+ +IN Y+ +IN +IN +IN IN3 IN4 -IN -Y -X GND GND X SWITCHES Y SWITCHES OFF ON ON OFF OFF OFF OFF OFF +REF +Y +X +VREF +VREF -REF -Y -X GND GND TABLE II. Input Configuration, Differential Reference Mode (SER/ DFR LOW). Copyright  ANPEC Electronics Corp. Rev. A.8 - Apr., 2002 8 www.anpec.com.tw APT7843 Single-Ended reference mode Figure 3 shows the diagram of single-ended reference mode. This application shows the measurement of current Y poisition is made by connecting the X+ input to the A/D converter, turning on the Y+ and Y- drivers, and digitizing the voltage on X+ . For this measurement, the resistance in the X+ lead does not affect the conversion. However, since the resistance between Y+ and Y- is fairly low, the on-resistance of the Y drivers does make a small difference. Under the situation outlined so far, it would not be possible to achieve a zero volt input or a full-scale input regardless of where the pointing device is on the touch screen because some voltage is lost across the internal switches. This situation can be remedied if use differential reference mode +Vcc Y+ Y+ X+ +IN +REF Converter -IN -REF Y- YY Switch ON GND Figure 4. Differential Reference Mode (SER/DF