Burr-Brown Products ADS7846 from Texas Instruments SBAS125H-SEPTEMBER 1999-REVISED JANUARY 2005 TOUCH SCREEN CONTROLLER FEATURES DESCRIPTION SAME PINOUT AS ADS7843 The ADS7846 is a next-generation version to the industry 2.2V TO 5.25V OPERATION standard ADS7843 4-wire touch screen controller.The INTERNAL 2.5V REFERENCE ADS7846 is 100%pin-compatible with the existing ADS7843, and drops into the same socket.This allows for easy upgrade DIRECT BATTERY MEASUREMENT (OV to 6V) of current applications to the new version.Only software ON-CHIP TEMPERATURE MEASUREMENT changes are required to take advantage of the added fea- TOUCH-PRESSURE MEASUREMENT tures of direct battery measurement,temperature measure- QSPITM/SPITM 3-WIRE INTERFACE ment,and touch-pressure measurement.The ADS7846 also has an on-chip 2.5V reference that can be used for the ●AUTO POWER-DOWN auxiliary input,battery monitor,and temperature measure- TSSOP-16,SSOP-16,QFN-16, ment modes.The reference can also be powered down when AND VFBGA-48 PACKAGES not used to conserve power.The internal reference operates down to 2.7V supply voltage while monitoring the battery APPLICATIONS voltage from OV to 6V. PERSONAL DIGITAL ASSISTANTS The low-power consumption of 0.75mW (typ at 2.7V, reference off),high speed(up to 125kHz clock rate),and on- PORTABLE INSTRUMENTS chip drivers make the ADS7846 an ideal choice for battery- POINT-OF-SALE TERMINALS operated systems such as personal digital assistants(PDAs) ●PAGERS with resistive touch screens,pagers,cellular phones,and TOUCH SCREEN MONITORS other portable equipment.The ADS7846 is available in the small TSSOP-16,SSOP-16,QFN-16,and VFBGA-48 pack- ●CELLULAR PHONES ages and is specified over the-40C to +85C temperature US Patent No.6246394 range. QSPI and SPI are registered trademarks of Motorola. PENIRO SAR ADS784 -O DOUT -O BUSY 0 +O DCLK Please be aware that an important notice concerning availability,standard warranty,and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. Copyright 1999-2005,Texas Instruments Incorporated testing of all parameters. TEXAS INSTRUMENTS www.ti.com
FEATURES ● SAME PINOUT AS ADS7843 ● 2.2V TO 5.25V OPERATION ● INTERNAL 2.5V REFERENCE ● DIRECT BATTERY MEASUREMENT (0V to 6V) ● ON-CHIP TEMPERATURE MEASUREMENT ● TOUCH-PRESSURE MEASUREMENT ● QSPITM/SPITM 3-WIRE INTERFACE ● AUTO POWER-DOWN ● TSSOP-16, SSOP-16, QFN-16, AND VFBGA-48 PACKAGES APPLICATIONS ● PERSONAL DIGITAL ASSISTANTS ● PORTABLE INSTRUMENTS ● POINT-OF-SALE TERMINALS ● PAGERS ● TOUCH SCREEN MONITORS ● CELLULAR PHONES TOUCH SCREEN CONTROLLER DESCRIPTION The ADS7846 is a next-generation version to the industry standard ADS7843 4-wire touch screen controller. The ADS7846 is 100% pin-compatible with the existing ADS7843, and drops into the same socket. This allows for easy upgrade of current applications to the new version. Only software changes are required to take advantage of the added features of direct battery measurement, temperature measurement, and touch-pressure measurement. The ADS7846 also has an on-chip 2.5V reference that can be used for the auxiliary input, battery monitor, and temperature measurement modes. The reference can also be powered down when not used to conserve power. The internal reference operates down to 2.7V supply voltage while monitoring the battery voltage from 0V to 6V. The low-power consumption of < 0.75mW (typ at 2.7V, reference off), high speed (up to 125kHz clock rate), and onchip drivers make the ADS7846 an ideal choice for batteryoperated systems such as personal digital assistants (PDAs) with resistive touch screens, pagers, cellular phones, and other portable equipment. The ADS7846 is available in the small TSSOP-16, SSOP-16, QFN-16, and VFBGA-48 packages and is specified over the –40°C to +85°C temperature range. CDAC Internal 2.5V Reference SAR ADS7846 Comparator 6-Channel MUX Serial Data Out Temperature Sensor Battery Monitor DOUT BUSY CS DCLK DIN VBAT AUX VREF +VCC X+ X– Y+ Y– PENIRQ ADS7846 SBAS125H – SEPTEMBER 1999 – REVISED JANUARY 2005 www.ti.com PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 1999-2005, Texas Instruments Incorporated US Patent No. 6246394 QSPI and SPI are registered trademarks of Motorola. AD ® S7846 ADS7846 ADS7846 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners
ABSOLUTE MAXIMUM RATINGS) ELECTROSTATIC +Vcc to GND -0.3Vto+6V Analog Inputs to GND -0.3V to +Vcc +0.3V DISCHARGE SENSITIVITY Digital Inputs to GND. -0.3V to +Vcc +0.3V Power Dissipation.250mw This integrated circuit can be damaged by ESD.Texas Instru- Maximum Junction Temperature +150°℃ ments recommends that all integrated circuits be handled with Operating Temperature Range .40°℃t0+85℃ appropriate precautions.Failure to observe proper handling Storage Temperature Range 65℃to+150℃ and installation procedures can cause damage. Lead Temperature (soldering,10s)..... .+300℃ NOTE:(1)Stresses above these ratings can cause permanent damage. ESD damage can range from subtle performance degradation Exposure to absolute maximum conditions for extended periods may degrade to complete device failure.Precision integrated circuits may be device reliability. more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. PACKAGE/ORDERING INFORMATION) MAXIMUM INTEGRAL SPECIFIED LINEARITY PACKAGE TEMPERATURE PACKAGE ORDERING PRODUCT ERROR (LSB) PACKAGE-LEAD DESIGNATOR RANGE MARKING NUMBER ADS7846E 轻 SSOP-16 DBQ 40°℃to+85℃ ADS7846E ADS7846E ADS7846E/2K5 ADS7846N 轻 TSSOP-16 PW -40°℃to+85℃ ADS7846N ADS7846N ADS7846N/2K5 ADS7846N/2K5G4 ADS78461 2 VFBGA-48 GQC 40°℃to+85C ADS7846 ADS7846IGQCR ADS7846I 积 QFN-16 RGV 40℃t0+85℃ ADS7846 ADS7846IRGVT ADS7846IRGVR NOTE:(1)For the most current package and ordering information,see the Package Option Addendum located at the end of this data sheet,or see the TI web site at www.ti.com. TEXAS 2 INSTRUMENTS ADS7846 www.ti.com SBAS125H
ADS7846 2 www.ti.com SBAS125H ABSOLUTE MAXIMUM RATINGS(1) +VCC to GND ........................................................................ –0.3V to +6V Analog Inputs to GND ............................................ –0.3V to +VCC + 0.3V Digital Inputs to GND ............................................. –0.3V to +VCC + 0.3V Power Dissipation .......................................................................... 250mW Maximum Junction Temperature ................................................... +150°C Operating Temperature Range ........................................ –40°C to +85°C Storage Temperature Range ......................................... –65°C to +150°C Lead Temperature (soldering, 10s) ............................................... +300°C NOTE: (1) Stresses above these ratings can cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. MAXIMUM INTEGRAL SPECIFIED LINEARITY PACKAGE TEMPERATURE PACKAGE ORDERING PRODUCT ERROR (LSB) PACKAGE-LEAD DESIGNATOR RANGE MARKING NUMBER ADS7846E ±2 SSOP-16 DBQ –40°C to +85°C ADS7846E ADS7846E "" " " " " ADS7846E/2K5 ADS7846N ±2 TSSOP-16 PW –40°C to +85°C ADS7846N ADS7846N "" " " " " ADS7846N/2K5 "" " " " " ADS7846N/2K5G4 ADS7846I ±2 VFBGA-48 GQC –40°C to +85°C ADS7846 ADS7846IGQCR ADS7846I ±2 QFN-16 RGV –40°C to +85°C ADS7846 ADS7846IRGVT "" " " " " ADS7846IRGVR NOTE: (1) For the most current package and ordering information, see the Package Option Addendum located at the end of this data sheet, or see the TI web site at www.ti.com. PACKAGE/ORDERING INFORMATION(1) ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications
ELECTRICAL CHARACTERISTICS At TA=-40C to +85C.+Vcc=+2.7V,VREF=2.5V internal voltage.fsAMPLE=125kHz,foLk=16.fsAMPLE=2MHz,12-bit mode,and digital inputs =GND or +Vcc. unless otherwise noted. ADS7846E PARAMETER CONDITIONS MIN TYP MAX UNITS ANALOG INPUT Full-Scale Input Span Positive Input-Negative Input 0 VREF Absolute Input Range Positive Input Negative Input +Vcc+0.2 +0.2 Capacitance Leakage Current 9 A SYSTEM PERFORMANCE Resolution Bits No Missing Codes 方 12 Bits Integral Linearity Error 2 LSB(1) Offset Error LSB Gain Error Extemal VREF LSB Noise Including Internal VREF 70 uVrms Power-Supply Rejection 70 dB SAMPLING DYNAMICS Conversion Time 12 CLK Cycles Acquisition Time 3 CLK Cycles Throughput Rate 125 kHz Multiplexer Settling Time 500 ns Aperture Delay Aperture Jitter Channel-to-Channel Isolation ViN 2.5Vp-p at 50kHz 100 B SWITCH DRIVERS On-Resistance Y+,X+ 6 Q Y-,X- Drive Current(2) Duration 100ms 50 mA REFERENCE OUTPUT Internal Reference Voltage 2.45 2.50 2.55 Internal Reference Drift 15 ppmC Quiescent Current 500 A REFERENCE INPUT Range 1.0 +Vcc Input Impedance SER/DFR =0.PD1=0. 1 GO Internal Reference Off Internal Reference On 250 0 BATTERY MONITOR Input Voltage Range 0.5 6.0 Input Impedance Sampling Battery kO Battery Monitor Off 1 Accuracy External VREF 2.5V -2 +2 % Intemal Reference -3 +3 TEMPERATURE MEASUREMENT Temperature Range -40 +85 C Resolution Differential Method(3) 1.6 TEMPO(4) . Accuracy Differential Method(3) 2 TEMP0(4) C DIGITAL INPUT/OUTPUT Logic Family CMOS Logic Levels,Except PENIRQ Vi |IH|≤+5uA +Vcc·0.7 +Vcc+0.3 1l|≤+5uA 0.3 +0.8 VoH 1oH=-250uA +Wcc·0.8 > o IoL =250uA 0.4 Dg的Fomat TA=0Cto+85℃，50k2Pu-Up 0.8 Straight Binary POWER-SUPPLY REQUIREMENTS +Vcc(5) Specified Performance 2.7 3.6 Operating Range 2.2 5.25 v Quiescent Current Internal Reference Off 280 650 Intemnal Reference On 780 fsAMPLE 12.5kHz 220 A Power-Down Mode with 3 CS=DCLK=DIN =+Vcc Power Dissipation +Vcc=+2.7V 1.8 mW TEMPERATURE RANGE Specified Performance -40 +85 ℃ NOTES:(1)LSB means least significant bit.With VREF equal to +2.5V.one LSB is 610uV.(2)Ensured by design,but not tested.Exceeding 50mA source current may result in device degradation.(3)Difference between TEMPO and TEMP1 measurement.No calibration necessary.(4)Temperature drift is -2.1mV/C. (5)ADS7846 operates down to 2.2V. ADS7846 TEXAS INSTRUMENTS 3 SBAS125H www.ti.com
ADS7846 3 SBAS125H www.ti.com ANALOG INPUT Full-Scale Input Span Positive Input-Negative Input 0 VREF V Absolute Input Range Positive Input –0.2 +VCC + 0.2 V Negative Input –0.2 +0.2 V Capacitance 25 pF Leakage Current 0.1 µA SYSTEM PERFORMANCE Resolution 12 Bits No Missing Codes 11 Bits Integral Linearity Error ±2 LSB(1) Offset Error ±6 LSB Gain Error External VREF ±4 LSB Noise Including Internal VREF 70 µVrms Power-Supply Rejection 70 dB SAMPLING DYNAMICS Conversion Time 12 CLK Cycles Acquisition Time 3 CLK Cycles Throughput Rate 125 kHz Multiplexer Settling Time 500 ns Aperture Delay 30 ns Aperture Jitter 100 ps Channel-to-Channel Isolation VIN = 2.5Vp-p at 50kHz 100 dB SWITCH DRIVERS On-Resistance Y+, X+ 5 Ω Y–, X– 6 Ω Drive Current(2) Duration 100ms 50 mA REFERENCE OUTPUT Internal Reference Voltage 2.45 2.50 2.55 V Internal Reference Drift 15 ppm/°C Quiescent Current 500 µA REFERENCE INPUT Range 1.0 +VCC V Input Impedance SER/DFR = 0, PD1 = 0, 1 GΩ Internal Reference Off Internal Reference On 250 Ω BATTERY MONITOR Input Voltage Range 0.5 6.0 V Input Impedance Sampling Battery 10 kΩ Battery Monitor Off 1 GΩ Accuracy External VREF = 2.5V –2 +2 % Internal Reference –3 +3 % TEMPERATURE MEASUREMENT Temperature Range –40 +85 °C Resolution Differential Method(3) 1.6 °C TEMP0(4) 0.3 °C Accuracy Differential Method(3) ±2 °C TEMP0(4) ±3 °C DIGITAL INPUT/OUTPUT Logic Family CMOS Logic Levels, Except PENIRQ VIH | IIH | ≤ +5µA +VCC • 0.7 +VCC + 0.3 VIL | IIL | ≤ +5µA –0.3 +0.8 V VOH IOH = –250µA +VCC • 0.8 V VOL IOL = 250µA 0.4 V PENIRQ VOL TA = 0°C to +85°C, 50kΩ Pull-Up 0.8 V Data Format Straight Binary POWER-SUPPLY REQUIREMENTS +VCC(5) Specified Performance 2.7 3.6 V Operating Range 2.2 5.25 V Quiescent Current Internal Reference Off 280 650 µA Internal Reference On 780 µA fSAMPLE = 12.5kHz 220 µA Power-Down Mode with 3 µA CS = DCLK = DIN = +VCC Power Dissipation +VCC = +2.7V 1.8 mW TEMPERATURE RANGE Specified Performance –40 +85 °C NOTES: (1) LSB means least significant bit. With VREF equal to +2.5V, one LSB is 610µV. (2) Ensured by design, but not tested. Exceeding 50mA source current may result in device degradation. (3) Difference between TEMP0 and TEMP1 measurement. No calibration necessary. (4) Temperature drift is –2.1mV/°C. (5) ADS7846 operates down to 2.2V. ADS7846E PARAMETER CONDITIONS MIN TYP MAX UNITS ELECTRICAL CHARACTERISTICS At TA = –40°C to +85°C, +VCC = +2.7V, VREF = 2.5V internal voltage, fSAMPLE = 125kHz, fCLK = 16 • fSAMPLE = 2MHz, 12-bit mode, and digital inputs = GND or +VCC, unless otherwise noted
PIN CONFIGURATION Top View SSOP,TSSOP Top View VFBGA DCLK DIN BUSY DOUT +Vcc 1 DCLK 2 3 5 X+ 2 cS A NC O 四 Y+ 34 DIN B○ © © © © © Q 太 BUSY +cc PENIRO Y- 5 ADS7846 43211 DOUT cO © 四 © © Q +Vcc GND 6 PENIRQ O © * © 四 © 四 Q VREF Vaur +Vcc 8 E○ 四 四 © © © Q AUX VREF AUX F© © © 四四 © X- Y-GND GND Top View QFN 5o0 odIN3d 9皇 9 BUSY 2 AUX DIN VaAT 23 ADS7846 10 GND DCLK Y- ooN PIN DESCRIPTION SSOP AND TSSOP PIN# VFBGA PIN QFN PIN NAME DESCRIPTION 1 B1 and C1 5 +Vcc Power Supply D1 X+ X+Position Input 3 7890 Y+ Y+Position Input 456 2 X-Position Input Y-Position Input G4 and G5 GND Ground G6 VBAT Battery Monitor Input 8910 ha 6 12 AUX Auxiliary Input to ADC er Voltage Reference Input/Output +Vo Digital 1/O Power Supply 1 B7 15 PENIRQ Pen Interrupt Open anode output (requires 10kn to 100k pull-up resistor extemally). DOUT Serial Data Output.Data is shifted on the falling edge of DCLK.This output is high impedance when CS is high. 13 A5 话 船 123 Busy Output.This output is high impedance when CS is high. 器 Serial Data Input.If CS is low,data is latched on rising edge of DCLK. pdontaeoCcW0nmntesesanpt6oiea 16 A2 4 DCLK Extemal Clock Input.This clock runs the SAR conversion process and synchronizes serial data VO. TEXAS 4 INSTRUMENTS ADS7846 www.ti.com SBAS125H
ADS7846 4 www.ti.com SBAS125H PIN CONFIGURATION Top View SSOP, TSSOP Top View VFBGA 1 2 3 4 5 6 7 8 +VCC X+ Y+ X– Y– GND VBAT AUX DCLK CS DIN BUSY DOUT PENIRQ +VCC VREF 16 15 14 13 12 11 10 9 ADS7846 NC A NC 1 2 3 4 5 6 7 DCLK +VCC +VCC X+ Y+ PENIRQ +VCC VREF AUX CS DIN BUSY DOUT X– Y– GND GND VBAT NC NC NC NC NC B C D E F NC NC NC NC NC NC NC NC NC NC NC NC NC NC NC NC NC NC NC NC NC NC G NC BUSY DIN CS DCLK AUX VBAT GND Y– 1 2 3 4 12 11 10 9 ADS7846 DOUT PENIRQ +VCC VREF 16 15 14 13 +VCC X+ Y+ X– 5 6 7 8 Top View QFN SSOP AND TSSOP PIN # VFBGA PIN # QFN PIN # NAME DESCRIPTION 1 B1 and C1 5 +VCC Power Supply 2 D1 6 X+ X+ Position Input 3 E1 7 Y+ Y+ Position Input 4 G2 8 X– X– Position Input 5 G3 9 Y– Y– Position Input 6 G4 and G5 10 GND Ground 7 G6 11 VBAT Battery Monitor Input 8 E7 12 AUX Auxiliary Input to ADC 9 D7 13 VREF Voltage Reference Input/Output 10 C7 14 +VCC Digital I/O Power Supply 11 B7 15 PENIRQ Pen Interrupt. Open anode output (requires 10kΩ to 100kΩ pull-up resistor externally). 12 A6 16 DOUT Serial Data Output. Data is shifted on the falling edge of DCLK. This output is high impedance when CS is high. 13 A5 1 BUSY Busy Output. This output is high impedance when CS is high. 14 A4 2 DIN Serial Data Input. If CS is low, data is latched on rising edge of DCLK. 15 A3 3 CS Chip Select Input. Controls conversion timing and enables the serial input/output register. CS high = power-down mode (ADC only). 16 A2 4 DCLK External Clock Input. This clock runs the SAR conversion process and synchronizes serial data I/O. PIN DESCRIPTION
TYPICAL CHARACTERISTICS At TA=+25C.+Vcc =+2.7V,VREF External +2.5V,fsAMPLE=125kHz,and foLk=16.fsAMPLE 2MHz,unless otherwise noted. POWER-DOWN SUPPLY CURRENT SUPPLY CURRENT vs TEMPERATURE vs TEMPERATURE 400 140 350 120 300 100 2 80 20 60 150 40 100 20 40 -20 0 20 40 60 80 100 40 -20 0 20 40 60 80 100 Temperature (C) Temperature (C) SUPPLY CURRENT vS +Vcc MAXIMUM SAMPLE RATE vs +Vcc 390 1M 370 50 fSAMPLE =12.5kHz 100K 30 3 10k 290 270 250 依 2.0 2.5 3.0 3.5 4.0 4.5 5.0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 +Vcc (V) +Vcc (V) CHANGE IN GAIN Vs TEMPERATURE CHANGE IN OFFSET Vs TEMPERATURE 0.15 0.6 0.10 0.4 (as7) 0.05 0.2 0 0 -0.05 0.2 0.10 0.4 0.15 0.6 40 -20 0 2040 60 80 100 40 -20 0 204060 80 100 Temperature (C) Temperature(C) ADS7846 TEXAS INSTRUMENTS SBAS125H www.ti.com
ADS7846 5 SBAS125H www.ti.com TYPICAL CHARACTERISTICS At TA = +25°C, +VCC = +2.7V, VREF = External +2.5V, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted. SUPPLY CURRENT vs TEMPERATURE –40 100 –20 0 40 20 Temperature (°C) Supply Current (µA) 400 350 300 250 200 150 100 60 80 POWER-DOWN SUPPLY CURRENT vs TEMPERATURE –40 100 –20 0 40 20 Temperature (°C) Supply Current (nA) 140 120 100 80 60 40 20 60 80 SUPPLY CURRENT vs +VCC 2.0 5.0 2.5 4.0 3.5 +VCC (V) Supply Current (µA) 390 370 350 330 310 290 270 250 3.0 4.5 f SAMPLE = 12.5kHz MAXIMUM SAMPLE RATE vs +VCC 2.0 5.0 2.5 4.0 3.5 +VCC (V) Sample Rate (Hz) 1M 100k 10k 1k 3.0 4.5 CHANGE IN GAIN vs TEMPERATURE –40 100 –20 0 40 20 Temperature (°C) Delta from +25°C (LSB) 0.15 0.10 0.05 0 –0.05 –0.10 –0.15 60 80 CHANGE IN OFFSET vs TEMPERATURE –40 100 –20 0 40 20 Temperature (°C) Delta from +25°C (LSB) 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 60 80
TYPICAL CHARACTERISTICS (Cont.) At TA=+25C.+Vcc =+2.7V,VREF=External +2.5V,fsAMPLE=125kHz,and fcu=16.fsAMPLE=2MHz.unless otherwise noted. REFERENCE CURRENT vs SAMPLE RATE REFERENCE CURRENT vs TEMPERATURE 18 16 10 14 12 6 10 2 8 0 6 0 25 50 75 100 125 40 -20 0 20 40 60 80 100 Sample Rate (kHz) Temperature (C) SWITCH-ON RESISTANCE vs +Vcc SWITCH-ON RESISTANCE vs TEMPERATURE (X+,Y+:+Vcc to Pin;X-,Y-:Pin to GND) (X+,Y+:+Vcc to Pin;X-.Y-:Pin to GND) 8 7 7 X- Y 6 5 X- g X+ Y+ 4 4 Y+ X+ 3 3 2 2 1 2.0 2.5 3.0 3.5 4.0 4.5 5.0 40 -20 0 20 40 60 80 100 +Vcc (V) Temperature (C) MAXIMUM SAMPLING RATE VS RIN INTERNAL VREF VS TEMPERATURE 2.0 2.4920 .8 ◆一INL:R=2k 2.4915 1 INL:R=500 ·DNLR=2k 2.4910 米-DNLR=500 2.4905 2.4900 0 2.4895 2.4890 0.4 2.4885 0.2 2.4880 0 2.4875 20 40 60 80100120140160180200 导号吊号8号号号○8ee88房8导导8388尺2品8 Sampling Rate (kHz) Temperature (C) TEXAS 6 INSTRUMENTS ADS7846 www.ti.com SBAS125H
ADS7846 6 www.ti.com SBAS125H TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, +VCC = +2.7V, VREF = External +2.5V, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted. REFERENCE CURRENT vs SAMPLE RATE 0 125 25 50 100 75 Sample Rate (kHz) Reference Current (µA) 14 12 10 8 6 4 2 0 REFERENCE CURRENT vs TEMPERATURE –40 100 –20 0 40 20 Temperature (°C) Reference Current (µA) 18 16 14 12 10 8 6 60 80 SWITCH-ON RESISTANCE vs TEMPERATURE (X+, Y+: +VCC to Pin; X–, Y–: Pin to GND) –40 100 –20 20 X+ Y+ X– Y– 40 Temperature (°C) RON (Ω) 1 8 7 6 5 4 3 2 0 60 80 2.4920 2.4915 2.4910 2.4905 2.4900 2.4895 2.4890 2.4885 2.4880 2.4875 Internal VREF (V) Temperature (°C) INTERNAL VREF vs TEMPERATURE –40 –35 –30 –25 –20 –15 –10 –05 0 05 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 SWITCH-ON RESISTANCE vs +VCC (X+, Y+: +VCC to Pin; X–, Y–: Pin to GND) 2.0 5.0 2.5 3.5 Y+ X+ Y– X– 4.0 +VCC (V) RON (Ω) 1 8 7 6 5 4 3 2 3.0 4.5 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 Error (LSB) 20 40 60 80 100 120 140 160 180 200 Sampling Rate (kHz) MAXIMUM SAMPLING RATE vs RIN INL: R = 2k INL: R = 500 DNL: R = 2k DNL: R = 500
TYPICAL CHARACTERISTICS (Cont.) At TA=+25C,+Vcc =+2.7V,VREF External +2.5V,fsAMPLE =125kHz,and fcLk 16.fsAMPLE 2MHz,unless otherwise noted. INTERNAL VREF VS VcC INTERNAL VREE Vs TURN-ON TIME 2.4865 100 2.4860 80 No Cap E 2.4855 60 (52μS) 12.Bt 1uF Cap Settling (1110uS) 2.4850 40 12-Bit Settling 2.4845 20 2.4840 0 9 9N恩&85g将99 0 200 400 600 800 1000 1200 Turn-On Time (uS) Vcc (V) TEMP DIODE VOLTAGE vs TEMPERATURE(2.7V SUPPLY) TEMPO DIODE VOLTAGE vs VsUPPLY(25C) 850 620 618 102.7mV 616 132.25mV 614 TEMPO 612 450 610 导号吊8闲#骨°8P988号8导导8888尺品品 2.7 3.0 3.3 Temperature(C) VsUPPLY (V) TEMP1 DIODE VOLTAGE vs VSUPPLY(25C) 732 730 728 726 724 722 2.7 3.0 3.3 VsUPPLY (V) ADS7846 TEXAS INSTRUMENTS SBAS125H www.ti.com
ADS7846 7 SBAS125H www.ti.com TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, +VCC = +2.7V, VREF = External +2.5V, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted. 2.4865 2.4860 2.4855 2.4850 2.4845 2.4840 VREF (V) 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 VCC (V) INTERNAL VREF vs VCC 850 800 750 700 650 600 550 500 450 TEMP Diode Voltage (mV) Temperature (°C) –40 –35 –30 –25 –20 –15 –10 –05 0 05 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 TEMP DIODE VOLTAGE vs TEMPERATURE (2.7V SUPPLY) 102.7mV 132.25mV TEMP0 TEMP1 100 80 60 40 20 0 Internal VREF (%) 0 200 400 600 800 1000 1200 INTERNAL VREF vs TURN-ON TIME Turn-On Time (µS) 1µF Cap (1110µS) 12-Bit Settling No Cap (52µS) 12-Bit Settling 620 618 616 614 612 610 2.7 3.0 3.3 VSUPPLY (V) TEMP0 DIODE VOLTAGE vs VSUPPLY (25°C) TEMP0 Diode Voltage (mV) 732 730 728 726 724 722 2.7 3.0 3.3 VSUPPLY (V) TEMP1 DIODE VOLTAGE vs VSUPPLY (25°C) TEMP1 Diode Voltage (mV)
THEORY OF OPERATION possible to negate the error from each touch panel driver switch's on-resistance (if this is a source of error for the The ADS7846 is a classic successive approximation register particular measurement). (SAR)analog-to-digital converter (ADC).The architecture is based on capacitive redistribution which inherently includes ANALOG INPUT a sample-and-hold function.The converter is fabricated on a 0.6um CMOS process. See Figure 2 for a block diagram of the input multiplexer on the ADS7846,the differential input of the ADC,and the The basic operation of the ADS7846 is shown in Figure 1. differential reference of the converter.Table I and Table ll The device features an internal 2.5V reference and an external clock.Operation is maintained from a single supply show the relationship between the A2.A1,A0,and SER/DFR of 2.7V to 5.25V.The internal reference can be overdriven control bits and the configuration of the ADS7846.The with an external,low impedance source between 1V and control bits are provided serially via the DIN pin-see the +Vcc.The value of the reference voltage directly sets the Digital Interface section of this data sheet for more details. input range of the converter. When the converter enters the hold mode,the voltage difference between the +IN and-IN inputs(see Figure 2)is The analog input (X-,Y-,and Z-position coordinates,auxil- captured on the internal capacitor array.The input current iary input,battery voltage,and chip temperature)to the converter is provided via a multiplexer.A unique configura- into the analog inputs depends on the conversion rate of the tion of low on-resistance touch panel driver switches allows device.During the sample period,the source must charge an unselected ADC input channel to provide power and its the internal sampling capacitor (typically 25pF).After the capacitor has been fully charged,there is no further input accompanying pin to provide ground for an external device, current.The rate of charge transfer from the analog source such as a touch screen.By maintaining a differential input to the converter and a differential reference architecture,it is to the converter is a function of conversion rate. +2.7V1o+5V 1uF ADS7846 10uF 0.1uf (Optional） DCLK 16 X+ cS 15 Chip Select Y+ DIN 14 Serial Data In Touch X- BUSY 13 Converter Status Screen Y- DOUT Serial Data Out To Battery 6 GND PENIRO 11 <Pen Interrupt VBAT +Vcc 10 Auxiliary Input O AUX 9 50k2 Voltage Regulator FIGURE 1.Basic Operation of the ADS7846. A2 A1 A0 VBAT AUXIN TEMP Y- Y+ Y-POSITION X-POSITION Z,-POSITION Z,-POSITION X-DRIVERS Y-DRIVERS 0 0 +IN (TEMPO) Off Off 0 +IN Measure Off On 0 1 0 Off Off 0 +lN Measure X-,On Y+, On 0 +IN Measure X-, On Y+, 0 01 +IN Measure On Off 1 1 +IN f Off +IN (TEMP1) O开 Off TABLE I.Input Configuration(DIN),Single-Ended Reference Mode(SER/DFR high). A2 A1 A0 +REF -REF Y- X+ Y+ Y-POSITION X-POSITION Z,-POSITION Z2-POSITION DRIVERS ON 0 1 Y+ Measure Y+,Y- 0 1 Y+ X- N Measure Y+,X- 1 0 0 Y+ X- +IN Measure Y+,X- 1 0 X+ X- +IN Measure X+,X- TABLE II.Input Configuration(DIN),Differential Reference Mode(SER/DFR low). TEXAS 8 INSTRUMENTS ADS7846 www.ti.com SBAS125H
ADS7846 8 www.ti.com SBAS125H THEORY OF OPERATION The ADS7846 is a classic successive approximation register (SAR) analog-to-digital converter (ADC). The architecture is based on capacitive redistribution which inherently includes a sample-and-hold function. The converter is fabricated on a 0.6µm CMOS process. The basic operation of the ADS7846 is shown in Figure 1. The device features an internal 2.5V reference and an external clock. Operation is maintained from a single supply of 2.7V to 5.25V. The internal reference can be overdriven with an external, low impedance source between 1V and +VCC. The value of the reference voltage directly sets the input range of the converter. The analog input (X-, Y-, and Z-position coordinates, auxiliary input, battery voltage, and chip temperature) to the converter is provided via a multiplexer. A unique configuration of low on-resistance touch panel driver switches allows an unselected ADC input channel to provide power and its accompanying pin to provide ground for an external device, such as a touch screen. By maintaining a differential input to the converter and a differential reference architecture, it is possible to negate the error from each touch panel driver switch’s on-resistance (if this is a source of error for the particular measurement). ANALOG INPUT See Figure 2 for a block diagram of the input multiplexer on the ADS7846, the differential input of the ADC, and the differential reference of the converter. Table I and Table II show the relationship between the A2, A1, A0, and SER/DFR control bits and the configuration of the ADS7846. The control bits are provided serially via the DIN pin—see the Digital Interface section of this data sheet for more details. When the converter enters the hold mode, the voltage difference between the +IN and –IN inputs (see Figure 2) is captured on the internal capacitor array. The input current into the analog inputs depends on the conversion rate of the device. During the sample period, the source must charge the internal sampling capacitor (typically 25pF). After the capacitor has been fully charged, there is no further input current. The rate of charge transfer from the analog source to the converter is a function of conversion rate. FIGURE 1. Basic Operation of the ADS7846. A2 A1 A0 VBAT AUXIN TEMP Y– X+ Y+ Y-POSITION X-POSITION Z1-POSITION Z2-POSITION X-DRIVERS Y-DRIVERS 0 00 +IN (TEMP0) Off Off 0 0 1 +IN Measure Off On 0 1 0 +IN Off Off 0 1 1 +IN Measure X–, On Y+, On 1 0 0 +IN Measure X–, On Y+, On 1 0 1 +IN Measure On Off 1 1 0 +IN Off Off 1 11 +IN (TEMP1) Off Off TABLE I. Input Configuration (DIN), Single-Ended Reference Mode (SER/DFR high). TABLE II. Input Configuration (DIN), Differential Reference Mode (SER/DFR low). A2 A1 A0 +REF –REF Y– X+ Y+ Y-POSITION X-POSITION Z1-POSITION Z2-POSITION DRIVERS ON 0 0 1 Y+ Y– +IN Measure Y+, Y– 0 1 1 Y+ X– +IN Measure Y+, X– 1 0 0 Y+ X– +IN Measure Y+, X– 1 0 1 X+ X– +IN Measure X+, X– +VCC X+ Y+ X– Y– GND VBAT AUX 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 DCLK CS DIN BUSY DOUT PENIRQ +VCC VREF Serial/Conversion Clock Chip Select Serial Data In Converter Status Serial Data Out + 1µF to 10µF (Optional) +2.7V to +5V ADS7846 Auxiliary Input To Battery Voltage Regulator Touch Screen 0.1µF Pen Interrupt 50kΩ
PENIRO +Vcc VREF TEMP1 、TEMPO A2-A0 SER/DFR (Shown 001B) (Shown High) X+ O Ref On/Off +REF +IN Y- Converter N 2.5V -REF Reference 75k2 2.5k Battery ●n AUX GND FIGURE 2.Simplified Diagram of Analog Input. INTERNAL REFERENCE Reference The ADS7846 has an intemnal 2.5V voltage reference that can Power Down be tumned on or off with the control bit,PD1=1(see Table V and Figure 3).Typically,the intemal reference voltage is only used in the single-ended mode for battery monitoring,temperature measurement,and for using the auxiliary input.Optimal touch screen performance is achieved when using the differential mode.The internal reference voltage of the ADS7846 must be Band Gap Buffer commanded to be off to maintain compatibility with the ADS7843. Therefore,after power-up,a write of PD1 =0 is required to insure the reference is off(see the Typical Characteristics for Optional To power-up time of the reference from power-down). CDAC FIGURE 3.Simplified Diagram of the Internal Reference. REFERENCE INPUT The voltage difference between +REF and-REF(shown in bit)size and is equal to the reference voltage divided by 4096 Figure 2)sets the analog input range.The ADS7846 oper- in 12-bit mode.Any offset or gain error inherent in the ADC ates with a reference in the range of 1V to +Vcc.There are appears to increase,in terms of LSB size,as the reference several critical items concerning the reference input and its voltage is reduced.For example,if the offset of a given wide voltage range.As the reference voltage is reduced,the converter is 2LSBs with a 2.5V reference,it is typically analog voltage weight of each digital output code is also 5LSBs with a 1V reference.In each case,the actual offset of reduced.This is often referred to as the LSB(least significant the device is the same,1.22mV.With a lower reference ADS7846 TEXAS INSTRUMENTS 9 SBAS125H www.ti.com
ADS7846 9 SBAS125H www.ti.com INTERNAL REFERENCE The ADS7846 has an internal 2.5V voltage reference that can be turned on or off with the control bit, PD1 = 1 (see Table V and Figure 3). Typically, the internal reference voltage is only used in the single-ended mode for battery monitoring, temperature measurement, and for using the auxiliary input. Optimal touch screen performance is achieved when using the differential mode. The internal reference voltage of the ADS7846 must be commanded to be off to maintain compatibility with the ADS7843. Therefore, after power-up, a write of PD1 = 0 is required to insure the reference is off (see the Typical Characteristics for power-up time of the reference from power-down). REFERENCE INPUT The voltage difference between +REF and –REF (shown in Figure 2) sets the analog input range. The ADS7846 operates with a reference in the range of 1V to +VCC. There are several critical items concerning the reference input and its wide voltage range. As the reference voltage is reduced, the analog voltage weight of each digital output code is also reduced. This is often referred to as the LSB (least significant bit) size and is equal to the reference voltage divided by 4096 in 12-bit mode. Any offset or gain error inherent in the ADC appears to increase, in terms of LSB size, as the reference voltage is reduced. For example, if the offset of a given converter is 2LSBs with a 2.5V reference, it is typically 5LSBs with a 1V reference. In each case, the actual offset of the device is the same, 1.22mV. With a lower reference FIGURE 2. Simplified Diagram of Analog Input. Converter –REF +REF +IN –IN VBAT AUX Battery On GND A2-A0 (Shown 001B) 2.5V Reference Ref On/Off SER/DFR (Shown High) X+ X– +VCC TEMP1 PENIRQ Y+ Y– VREF TEMP0 7.5kΩ 2.5kΩ Buffer Band Gap Reference Power Down To CDAC Optional VREF FIGURE 3. Simplified Diagram of the Internal Reference
voltage,more care must be taken to provide a clean layout +Vcc including adequate bypassing,a clean(low-noise,low-ripple) power supply,a low-noise reference(if an external reference is used),and a low-noise input signal. The voltage into the VREF input directly drives the capacitor ● digital-to-analog converter(CDAC)portion of the ADS7846. Y+ Therefore,the input current is very low(typically 13uA). There is also a critical item regarding the reference when making measurements where the switch drivers are on.For 了WW- IN +REF this discussion,it is useful to consider the basic operation of Converter the ADS7846 (see Figure 1).This particular application -IN shows the device being used to digitize a resistive touch -REF screen.A measurement of the current Y position of the pointing device is made by connecting the X+input to the Y ADC,turning on the Y+and Y-drivers,and digitizing the voltage on X+(Figure 4 shows a block diagram).For this GND O measurement.the resistance in the X+lead does not affect the conversion (it does affect the settling time,but the FIGURE 5.Simplified Diagram of Differential Reference resistance is usually small enough that this is not a concem). (SER/DFR Low.Y Switches Enabled.X+is However,since the resistance between Y+and Y-is fairly Analog Input). low,the on-resistance of the Y drivers does make a small difference.Under the situation outlined so far,it is not As a final note about the differential reference mode,it must possible to achieve a OV input or a full-scale input regardless be used with +Vcc as the source of the +REF voltage and of where the pointing device is on the touch screen,because cannot be used with VREF.It is possible to use a high some voltage is lost across the internal switches.In addition. precision reference on VREF and single-ended reference the internal switch resistance is unlikely to track the resis- mode for measurements which do not need to be ratiometric. tance of the touch screen,providing an additional source of error In some cases,it is possible to power the converter directly from a precision reference.Most references can provide enough power for the ADS7846,but might not be able to +Vcc supply enough current for the external load (such as a resistive touch screen). TOUCH SCREEN SETTLING In some applications,extemal capacitors may be required across the touch screen for filtering noise picked up by the touch screen(for example,noise generated by the LCD panel WWx° N +REF or backlight circuitry).These capacitors provide a low-pass Converter filter to reduce the noise,but cause a settling time requirement REF when the panel is touched that typically shows up as a gain error.The problem is that the input and/or reference has not Y settled to the final steady-state value prior to the ADC sam- pling the input(s)and providing the digital output.Additionally. GND O the reference voltage may still be changing during the mea- surement cycle.There are several methods for minimizing or FIGURE 4.Simplified Diagram of Single-Ended Reference eliminating this issue.Option 1 is to stop or slow down the (SER/DFR High,Y Switches Enabled,X+is ADS7846 DCLK for the required touch screen settling time. Analog Input). This allows the input and reference to have stable values for the Acquire period(3 clock cycles of the ADS7846;see Figure This situation can be remedied as shown in Figure 5.By 9).This works for both the single-ended and the differential setting the SER/DFR bit low,the +REF and-REF inputs are modes.Option 2 is to operate the ADS7846 in the differential connected directly to Y+and Y-,respectively,which makes mode only for the touch screen measurements and command the analog-to-digital conversion ratiometric.The result of the the ADS7846 to remain on(touch screen drivers on)and not conversion is always a percentage of the external resistance, go into power-down(PDO 1).Several conversions are made regardless of how it changes in relation to the on-resistance of depending on the settling time required and the ADS7846 data the internal switches.Note that there is an important consid- rate.Once the required number of conversions have been eration regarding power dissipation when using the ratiometric made,the processor commands the ADS7846 to go into the mode of operation (see the Power Dissipation section for power-down state on the last measurement.This process is more details). TEXAS 10 INSTRUMENTS ADS7846 www.ti.com SBAS125H
ADS7846 10 www.ti.com SBAS125H voltage, more care must be taken to provide a clean layout including adequate bypassing, a clean (low-noise, low-ripple) power supply, a low-noise reference (if an external reference is used), and a low-noise input signal. The voltage into the VREF input directly drives the capacitor digital-to-analog converter (CDAC) portion of the ADS7846. Therefore, the input current is very low (typically < 13µA). There is also a critical item regarding the reference when making measurements where the switch drivers are on. For this discussion, it is useful to consider the basic operation of the ADS7846 (see Figure 1). This particular application shows the device being used to digitize a resistive touch screen. A measurement of the current Y position of the pointing device is made by connecting the X+ input to the ADC, turning on the Y+ and Y– drivers, and digitizing the voltage on X+ (Figure 4 shows a block diagram). For this measurement, the resistance in the X+ lead does not affect the conversion (it does affect the settling time, but the resistance is usually small enough that this is not a concern). 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 is not possible to achieve a 0V 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. In addition, the internal switch resistance is unlikely to track the resistance of the touch screen, providing an additional source of error. FIGURE 4. Simplified Diagram of Single-Ended Reference (SER/DFR High, Y Switches Enabled, X+ is Analog Input). This situation can be remedied as shown in Figure 5. By setting the SER/DFR bit low, the +REF and –REF inputs are connected directly to Y+ and Y–, respectively, which makes the analog-to-digital conversion ratiometric. The result of the conversion is always a percentage of the external resistance, regardless of how it changes in relation to the on-resistance of the internal switches. Note that there is an important consideration regarding power dissipation when using the ratiometric mode of operation (see the Power Dissipation section for more details). FIGURE 5. Simplified Diagram of Differential Reference (SER/DFR Low, Y Switches Enabled, X+ is Analog Input). Converter +IN +REF Y+ +VCC X+ Y– GND –REF –IN As a final note about the differential reference mode, it must be used with +VCC as the source of the +REF voltage and cannot be used with VREF. It is possible to use a high precision reference on VREF and single-ended reference mode for measurements which do not need to be ratiometric. In some cases, it is possible to power the converter directly from a precision reference. Most references can provide enough power for the ADS7846, but might not be able to supply enough current for the external load (such as a resistive touch screen). TOUCH SCREEN SETTLING In some applications, external capacitors may be required across the touch screen for filtering noise picked up by the touch screen (for example, noise generated by the LCD panel or backlight circuitry). These capacitors provide a low-pass filter to reduce the noise, but cause a settling time requirement when the panel is touched that typically shows up as a gain error. The problem is that the input and/or reference has not settled to the final steady-state value prior to the ADC sampling the input(s) and providing the digital output. Additionally, the reference voltage may still be changing during the measurement cycle. There are several methods for minimizing or eliminating this issue. Option 1 is to stop or slow down the ADS7846 DCLK for the required touch screen settling time. This allows the input and reference to have stable values for the Acquire period (3 clock cycles of the ADS7846; see Figure 9). This works for both the single-ended and the differential modes. Option 2 is to operate the ADS7846 in the differential mode only for the touch screen measurements and command the ADS7846 to remain on (touch screen drivers on) and not go into power-down (PD0 = 1). Several conversions are made depending on the settling time required and the ADS7846 data rate. Once the required number of conversions have been made, the processor commands the ADS7846 to go into the power-down state on the last measurement. This process is Converter +IN +REF Y+ +VCC VREF X+ Y– GND –REF –IN