Touch Screen Controller

APT7846 Touch Screen Controller 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 1 Auxiliary Analog Input Full Power Down Control Internal Bandgap Reference Serial Interface To Microprocessor Description The APT7846 is enhance function of APT7843 added battery and temperature monitor function and offer of a bandgap reference voltage for system user. The APT7846 Touch Screen Controller IC provides all the screen driver , 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 1 auxiliary input to A/D converter , allowing for the measurement of other input signal. Pin Assignment Applications www.DataSheet4U.com +Vcc 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 DCLK CS DIN BUSY DOUT PENIRQ +Vcc V4-. • • • • • PDAs Hand held computer Touch-screen mobile phone Protable electronic dictionary Smart IA X+ Y+ XYGND V*)6 IN Ordering Information APT7846 Handling Code Temp. Range Package Code Package Code N : SSOP Temp. Range I : - 40 to 85 °C Handling Code TU : Tube O : TSSOP TR : Tape & Reel 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.6 - Dec., 2001 1 www.anpec.com.tw APT7846 Block Diagram PENIRQ X+ XY+ YScreen Driver 12 Bit or 8 Bit A/D Converter MUX Serial Interface DCLK CS DIN V*)6 IN Internal Reference DOUT BUSY V4-. Pin Description PIN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 NAME +Vcc X+ Y+ XYGND V*)6 IN V4-. +Vcc PENIRQ DOUT BUSY DIN CS DCLK DESCRIPTION Power Supply , 2.7V 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 Measure Battery Input. Auxiliary input of A/D converter. Voltage Reference Input or Output. Power Supply , 2.7V to 5V. Pen interrupt. (requires to 100kΩ pull-up resistor externally) Serial Data Output. This output is high impedance when CS is HIGH. Busy Output. This output is high impedance whenCS is HIGH. Serial Data input. Chip Select. (Active Low) Serial Clock. Copyright  ANPEC Electronics Corp. Rev. A.6 - Dec., 2001 2 www.anpec.com.tw APT7846 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. PARAMETER DC ACCURACY Resolution No missing code Integral Nonlinearity Offset Error Offset Error Match Gain Error Gain Error Match Noise Power Supply Rejection REFERENCE INPUT VREF Input Voltage Range DC Leakage Current VREF Input Impedance VREF Input Current FSAMPLE = 12.5 kHz CS = Vcc REFERENCE OUTPUT Internal Reference Voltage Input Impedence DYNAMIC PERFORMANCE 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- , X4 4 15 15 Ω Ω 3 125 12 DCLK cycles DCLK cycles KSPS VIN = 2.5Vp-p ; FIN = 50kHz 30 100 100 ns ps dB Internal Reference Off 2.4 2.5 1 2.6 V GΩ CS = GND or Vcc 1.0 ±1 5 13 2.5 3 40 Vcc µA GΩ µA µA µA 0.1 30 70 0.1 11 ±2 ±6 1 ±4 1 12 Bits Bits LSB LSB LSB LSB LSB uV rms dB CONDITIONS APT7846 MIN TYP MAX UNIT Copyright  ANPEC Electronics Corp. Rev. A.6 - Dec., 2001 3 www.anpec.com.tw APT7846 Electrical Characteristics (Cont.) PARAMETER LOGIC INPUTS Input High Voltage , V I N H Input Low Voltage , V I N L Input Current , I I N Input Capacitance , C I N LOGIC OUTPUTS Output High Voltage , V O H Output Low Voltage , V O L PENIRQ output low voltage , V O L Floating-State Leakage Current Floating-State Output Capacitance Output Coding ANALOG INPUT Input Voltage Ranges DC Leakage Current Input Capacitance POWER REQUIREMENTS Vcc Icc Normal Mode (Static) Normal Mode (FSAMPLE = 12.5kSPS) Shutdown Mode(Static) Showdown BATTERY MEASURE Input Voltage Range Input impedance Sample Battery On Sample Battery Off Accuracy TEMPERATURE RANGE Normal Operation -40 85 °C V R EF -2 10 1 2 KΩ GΩ % 0.5 6 V Vcc = 3.6V Digital I/Ps =0V or Vcc Vcc = 3.6V Vcc = 3.6V 650 540 3 3.6 µA µA µA µW 2.7 3.6 V 0 ± 0.1 30 V R EF V µA pF |I O H | ≤ -250µA |I O L | ≤ 250µA Vcc –0.2 CONDITIONS APT7846 MIN 2.4 0.8 ±1 10 TYP MAX UNIT |I I N H | ≤ +5µA |I I N L | ≤ +5µA V V µA pF V 0.4 0.2 ± 10 10 V V µA pF Straight ( Natural ) Binary Note : (1) LSB means least Significant Bit. With VREF equal to +2.5V , one LSB is 610µV Copyright  ANPEC Electronics Corp. Rev. A.6 - Dec., 2001 4 www.anpec.com.tw APT7846 Chip Overview The APT7846 is a successive approximation analog-to-digital (A/D) converter based around a capacitive redistribution DAC. Figure 1 show basic operation of the APT7846. The APT7846 communicates via a 4-wire serial interface. The device requires an external reference voltage Vref. The value of the reference voltage directly sets the input range of the converter. Otherwise you can use internal reference Voltage to do conversion. The APT7846 primary function is to control resistive touchscreens. When a touch is detected , pen interrupt pin will go low to wake up extenal microprocessor . The microprocessor writes register to initiate +2.7V to +5v 1uF to 10uF (Optional) conversion. This A/D converter may also be used to measure voltage presented on the IN Pin or to measure battery presented on the VBAT Pin. Analog Input The analog input to the converter is provided via a four-channel multiplexer. Figure 2 shows a simplified diagram of the APT7846 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/,.4 and the configuration of the APT7846. See the section of single-ended reference mode and differential reference mode for more details. 0.1uF 1 2 APT7846 +Vcc X+ Y+ XYGND VBAT IN DCLK CS DIN BUSY DOUT PENIRQ +Vcc VREF 16 15 14 13 12 11 10 9 To Touch Screen 3 4 5 6 Connect to Microprossor Battery Input Auxiliary Input 7 8 0.1uF 100k ohm (optional) FIGURE 1. Basic Operation of the APT7846 Copyright  ANPEC Electronics Corp. Rev. A.6 - Dec., 2001 5 www.anpec.com.tw APT7846 PENIRQ TEMP 1 TEMP 0 +Vcc VREF A2-A0 (Shown 001B) SER/DFR (Shown HIGH) Ref ON/OFF X+ X- Y+ Y- +IN -IN +REF CONVERTER -REF 2.65V Reference VBAT 7.5K Ω 2.5K Ω IN GND Battery On FIGURE 2. Simplified Diagram of Analog Input A2 0 0 0 0 1 1 1 1 A1 0 0 1 1 0 0 1 1 A0 0 1 0 1 0 1 0 1 +IN +IN(TEMP 1) VBAT AUXIN TEMP +IN(TEMP 0) Y- X+ +IN Y+ Y-POSITION Measure XZ1Z2XYPOSITION POSITION POSITION DRIVERS DRIVERS OFF OFF OFF OFF Measure Measure X-,ON X-,ON ON OFF OFF ON OFF Y+,ON Y+,ON OFF OFF OFF +IN +IN +IN +IN Measure TABLE I. Input Configuration , Single-Ended Reference Mode (SER/ ,.4 HIGH). A2 0 0 1 1 A1 0 1 0 0 A0 1 1 0 1 +REF -REF Y+ YY+ XY+ XX+ XYX+ +IN +IN Y+ Y-POSITION X-POSITION Z1-POSITION Z2-POSITION DRIVERS ON Measure Y+,YMeasure Y+,XMeasure Y+,XMeasure X+,X- +IN +IN TABLE II. Input Configuration , Differential Reference Mode (SER/ ,.4 LOW). Copyright  ANPEC Electronics Corp. Rev. A.6 - Dec., 2001 6 www.anpec.com.tw APT7846 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 +Vcc Y+ Y+ X+ +IN +REF Converter -IN -REF Y- YY Switch ON GND Figure 4. Differential Reference Mode (SER/,.4 LOW , A2=Low , A1=Low , A0=High) Serial Interface Data is written to , and read from , the APT7846 via the serial port. The serial port has 4 pins - serial clock (DCLK) , chip select ( CS) , data in (DIN) and data out (DOUT). The DCLK acts on the rising edge. The CS acts as a reset for the serial port with +5 goes low initiating a conversion cycle. The cycle consists of 2 parts - a write followed by a read. Figure 5 shows the typical timing of the APT7846’s serial interface. A total of 24 clock cycles will complete one conversion. Also shown in Figure 5 is the placement and order of the control bits within the control byte. Tables III and IV give detailed information about these bits. The first bit , the ′S′ bit , must always be HIGH and indicates the start of the control byte. The APT7846 will ignore inputs on the DIN pin until the start bit S detected. The next three bits (A2 - A0) select the active input channel or channels of the input multiplexer (see Tables I and II and Figure 2). The MODE bit determines the number of bits for each conversion , either 12 bits (LOW) or 8 bits (HIGH). The SER/,.4 bit controls the reference mode: either single-ended (HIGH) or differential (LOW). (The differential mode is also referred to as the ratiometric conversion mode.) The last two bits (PD1 - PD0) select the power- down mode as shown in Table V. If both inputs are HIGH , the device is always powered up. If both inputs are LOW , the device enters a power-down mode between conversions. 7 www.anpec.com