DATASHEET MK712 TOUCH SCREEN CONTROLLER Description Features The MK712 Touch Screen Controller IC provides all the screen drive, A to D converter and control circuits to easily interface to 4-wire analog resistive touch screens. • Packaged in 28-pin SSOP (150 mil) or 28-pin SOIC (300 The IC continually monitors the screen waiting for a touch. In this mode, the supply current is typically 0.5µA. When the screen is touched, the IC performs analog to digital conversions to determine the location of the touch, stores the X and Y locations in the registers, and issues an interrupt. This process is repeated up to 197 times per second until no further screen touches are detected, at which time the low current mode is resumed. and automotive (-35°C to +85°C) temperature ranges mil) • Industrial (-30°C to +70°C) and commercial (0 to +70°C) • • • • • • • • • • • • • • Block Diagram • • • Available in Pb (lead) free Fully integrated, lowest power solution Low standby current of 0.5µA (typical) at 5.0 V Active current while converting less than 10 mA Resolves 350 dots/inch on 10.5” display Maximum speed of 197 points/second Ratio metric conversion may eliminate screen calibration Automatically wakes up and goes back to standby 3.3 V or 5 V supply 12 bit A/D converter Simplifies the writing of software for touch screens Extended temperature range available Capacitors are the only external components required Touch screen is directly driven - no external transistors are required Programmable conversion rate A to D Converter is monotonic Parallel interface Pin Assignment IDT™ / ICS™ TOUCH SCREEN CONTROLLER 1 NC 1 28 D0 INT 2 27 D1 TOUCH 3 26 D2 VDD 4 25 D3 VDD 5 24 D4 XH 6 23 D5 XL 7 22 VDD YH 8 21 GND YL 9 20 D6 GND 10 19 D7 GND 11 18 CLKIN WR 12 17 A0 RD 13 16 A1 CS 14 15 A2 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Pin Descriptions Pin Number Pin Name Pin Type Pin Description 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 NC INT TOUCH VDD VDD XH XL YH YL GND GND WR RD CS A2 A1 A0 CLKIN D7 D6 GND VDD D5 D4 D3 D2 D1 D0 — Output Output Power Power Touch Screen Pin Touch Screen Pin Touch Screen Pin Touch Screen Pin Power Power Input Input Input Input Input Input Input I/O I/O Power Power I/O I/O I/O I/O I/O I/O No connect. Do not connect this pin to anything. Interrupt. Goes high to signal an interrupt. Cleared on next read. Touch signal. Goes low when screen is touched. Goes high when not touched. Power Supply. Connect to +5 V or +3.3 V. (Connect all VDDs to same voltage) Power Supply. Connect to +3.3 V. Connect to X-high on touch screen. (Right side) Connect to X-low on touch screen. (Left side) Connect to Y-high on touch screen. (Top) Connect to Y-low on touch screen. (Bottom) Connect to ground. Connect to ground. Write enable. Active low. Read enable. Active low. Chip select. Active low. Register address 2. Register address 1. Register address 0. Clock input. Typically 14.3 MHz. Best if driven by an ICS clock synthesizer. Data bit 7. Data bit 6. Connect to ground. Power Supply. Connect to +5 V or +3.3 V. (Connect all VDDs to same voltage) Data bit 5. Data bit 4. Data bit 3. Data bit 2. Data bit 1. Data bit 0. Interrupts Interrupts are controlled by register 6 (see Register Description). The INT pin (pin 2) goes high to signal an interrupt. Interrupts are then cleared by reading any register. However, if the MK712 is in the process of generating an interrupt during a read cycle, then the interrupt is not cleared and INT will stay high. This internal process may take 100ns, and so to guarantee that the interrupt is cleared, two successive read cycles may be necessary. IDT™ / ICS™ TOUCH SCREEN CONTROLLER 2 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL IC Operation IDT™ / ICS™ TOUCH SCREEN CONTROLLER 3 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Register Description The MK712 register set is designed to be compatible with the Gazelle pen digitizer registers allowing a software driver for the Gazelle digitizer to be used with the MicroClock MK712. The eight 8-bit registers are defined below: IDT™ / ICS™ TOUCH SCREEN CONTROLLER 4 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Rate Register (Register 7) Programming Calculating Points Per Second The formula for determining P.P.S. is: Power-On Reset On application of power, an internal reset is generated that clears all bits in registers 0, 1, and 6. Register 7 is set to 32 giving a rate of 86 PPS. Note that clearing register 6 puts the IC into the power down condition. Initializing the MK712 The interrupt on the MK712 can only be cleared by reading a register or by writing register 6 to the power down condition. After a fault condition, initialize the MK712 by writing register 6 to zero and then writing register 6 to the desired value. This will always clear pending interrupts. IDT™ / ICS™ TOUCH SCREEN CONTROLLER 5 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Recommended Circuit Pen Bounce When the screen is untouched, the Y plate is driven high and the X plate is driven low. When the screen is touched, the X plate is pulled high, which is detected by the MK712. This initiates a conversion (as long as periodic conversions are enabled). Some de-bounce is provided by the time constant of the screen decoupling capacitors combined with the screen resistance. However, once conversions have started, pen bounce will not be detected until after both the X and Y points have been taken. If the pen is lifted during a conversion, this will also not be detected until the conversion is complete. This is typically indicated by a point with the correct Y coordinates, but minimum (for that screen) X coordinates. Screen Decoupling The component values suggested should give excellent results. However, for screens with a high resistance operating at a high conversion rate, extra interrupts may be issued. This is because the time constant of the screen decoupling capacitors and screen resistance is high, resulting in the screen appearing to be untouched and then touched between conversions. These extra interrupts can be eliminated by reducing the size of the screen decoupling capacitors on pins XH, XL, YH, and YL. This will, however, slightly reduce the noise rejection, which could decrease the accuracy of the conversion. IDT™ / ICS™ TOUCH SCREEN CONTROLLER 6 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Optimizing Performance when Reading and Writing Registers Reading and writing the MK712 generates digital noise that may reduce the accuracy of the A to D converter. This noise has several causes, including board layout, data bus loading, and power supply voltage. By appropriately timing the register operations, the effects of this noise can be minimized. After an interrupt is issued, the MK712 allows a minimum of 1 millisecond to elapse before initiating the conversion cycle. This allows the screen drivers to settle. For best performance, complete all register operations within this 1ms window after an interrupt. Power Down/Stopping the Clock If the screen is untouched, the supply current is under 3µA. If the input clock is stopped, the supply current is also less than 3µA. When the screen is touched with no clock, TOUCH goes low and INT goes high, but no further operations occur until the clock starts. A to D conversions are invalid until after the clock has stabilized at the correct frequency and one full conversion cycle has been completed. Input Clock The MK712 is highly tolerant of different clock frequencies (from 12 to 20 MHz), rise times, and duty cycles. However, any input clock undershoot or overshoot will cause the MK712 to draw extra current. This can be eliminated by using a MicroClock clock synthesizer and properly terminating the clock driver. MicroClock makes low power clock synthesizers with 14.3 MHz power down. Resistive Touch Screen (4-wire) Resistive touch screens consist of 2 resistive plates that are separated by a small gap. Each plate has an electrode at each end and when the screen is touched, the two plates are shorted together at that point. If a voltage is applied, for example, between XL and XH, then a voltage divider is formed on the X PLATE. When the Y PLATE is touched to the X PLATE, a voltage will be developed on the Y PLATE that is proportional to distance of the touch from XL and XH. By accurately measuring this voltage, the position of the touch can be determined. IDT™ / ICS™ TOUCH SCREEN CONTROLLER 7 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Recommended Method for Reading Points If the user is pressing lightly on the touch screen, it is likely that the screen contact will be intermittent. The screen will bounce, causing false points. This effect can be reduced by insuring that the screen is touched both before and after a conversion. By doing this, the first and last point in a series of points are discarded. The following algorithm checks that a point has valid touches both before and after a conversion, and it distinguishes between change-in-touch interrupts and conversion complete interrupts. Register 6 bits 0, 1, and 2 must all be true (logical 1) in order to use this method. Warning–When Using a Switching Regulator Power Supply When using the MK712 in a system where the power is supplied by a switching regulator, do not perform screen conversions when the regulator is operating in the power saving mode. Some switching regulators feature a low power mode (for example, Linear Technology’s “Burst Mode”) where the output is turned on and off in order to save power. The extra power supply noise generated when using this mode causes spurious data points to be returned from the MK712, so it should be disabled when the MK712 is doing screen conversions. IDT™ / ICS™ TOUCH SCREEN CONTROLLER 8 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Analog to Digital Converter Option The 12-bit ADC converts X and Y co-ordinates at a rate determined by registers 6 and 7. The converter uses a ratiometric technique to give absolute co-ordinates on the screen, largely independent of variations in screen resistance, temperature or power supply voltage. The total voltage applied across the screen is defined as full-scale for the converter (i.e. 4095) and any point touched on the screen is proportional to this. For example, if the screen is touched exactly in the center, the converter will read 2047. This feature may allow for the elimination of calibration upon startup. However, the full scale voltage is defined at the IC pins and so any parasitic interconnect resistance will be included in full scale. In addition, the interconnect resistances on the screen also account for about 20% of the total resistance. This means that approximately the bottom 10% and top 10% of full scale are inaccessible. The converter is guaranteed to be monotonic, with no missing codes. IDT™ / ICS™ TOUCH SCREEN CONTROLLER 9 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Absolute Maximum Ratings Stresses above the ratings listed below can cause permanent damage to the MK712. These ratings, which are standard values for ICS commercially rated parts, are stress ratings only. Functional operation of the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods can affect product reliability. Electrical parameters are guaranteed only over the recommended operating temperature range. Item Rating Supply Voltage, VDD (referenced to ground) 7V All Inputs and Outputs (referenced to ground) -0.5 V to VDD+0.5 V Ambient Operating Temperature (commercial) 0 to +70° C Ambient Operating Temperature (industrial) -30 to +70° C Ambient Operating Temperature (automotive) -35 to +85° C Storage Temperature -65 to +150° C Junction Temperature 125° C Soldering Temperature (10 to 20 seconds max) 260° C Recommended Operation Conditions Parameter Min. Max. Units 0 +70 °C Ambient Operating Temperature (industrial) -30 +70 °C Ambient Operating Temperature (automotive) -35 +85 °C Power Supply Voltage (measured in respect to GND) (commercial and industrial) +3.0 +5.5 V Power Supply Voltage (measured in respect to GND) (automotive) +3.135 +5.5 V Ambient Operating Temperature (commercial) IDT™ / ICS™ TOUCH SCREEN CONTROLLER 10 Typ. MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL DC Electrical Characteristics Unless stated otherwise,VDD = 3.3 V or 5V, TA = 0 to +70° C (commercial), -30°C to +70°C (industrial), -35°C to +85°C (automotive) Parameter Symbol Conditions Min. Typ. Max. Units 3.0 5.5 V 3.135 5.5 V Operating Voltage VDD Commercial and industrial Operating Voltage VDD Automotive Input High Voltage VIH VDD=5 V Input Low Voltage VIL VDD=5 V Output High Voltage VOH IOH = -2 mA VDD-0.4 V Output High Voltage VOH VDD=5 V, IOH = -12 mA 2.4 V Output Low Voltage VOL VDD=5 V, IOL = 12 mA Input High Voltage VIH VDD=3.3 V Input Low Voltage VIL VDD=3.3 V Output High Voltage VOH VDD=3.3 V, IOH = -8 mA Output Low Voltage VOL VDD=3.3 V, IOL = 8 mA Operating Supply Current IDD At VDD=5 V, 300Ω screen, 100 PPS 5 mA At VDD=3.3 V, Note 3 3 mA Standby, Clock, Note 4 0.5 3 µA Standby, Note 5 0.5 3 µA Power down, PD=0 or PD=1, no clock 0.2 3 µA Each output ±50 mA 7 pF Short Circuit Current IOS Input Capacitance CIN IDT™ / ICS™ TOUCH SCREEN CONTROLLER 11 2 V 0.8 0.4 1.9 V V V 0.4 2.4 V V 0.4 MK712 V REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL AC Electrical Characteristics Unless stated otherwise,VDD = 3.3 V or 5 V, TA = 0 to +70° C (commercial), -30°C to +70°C (industrial), -35°C to +85°C (automotive) Parameter Symbol Conditions Min. Typ. Max. Units 14.32 20 MHz 75 % Input Clock Frequency, pin 18 Note 1 12 Input Clock Duty Cycle, pin 18 At 1.5 V 25 Output Rise Time tOR 0.8 to 2.0 V, VDD=5 V 3 ns Output Fall Time tOF 2.0 to 0.8 V, VDD=5 V 3 ns 12 bits ±2 LSB 2000 Ω Resolution Non-linearity Monotonic, Note 2 Touch Screen Resistance 100 Note 1: Consult with ICS about the best device to use to generate the input clock. Note 2: With no missing codes. Note 3: Assumes no 14.3 MHz input clock overshoot, 300Ω screen, 100 PPS. Note 4: Assumes no 14.3 MHz input clock overshoot, no touch. Note 5: With no touch, no clock. IDT™ / ICS™ TOUCH SCREEN CONTROLLER 12 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Register Interface Timing Number Symbol Description Min. Max. Units Note Read and Write Cycles 1 TRASC Address Setup to CS Low 5 ns 2 TRAHC Address Hold from CS High 0 ns 3 TRCCY CS High to CS Low 40 ns Read Cycle Only 4 TRSCR CS Low to RD Low 10 ns 5 TRRD RD Pulse Width 40 ns 6 TRCHR1 RD High to CS High 0 ns 7 TRCHR2 RD High to CS Low 40 ns 8 TRDC CS Low to Data 35 ns 9 TRDR RD Low to Data 35 ns 10 TRDHC CS High to Data Release 2 20 ns 1 11 TRDHR RD High to Data Release 2 20 ns 1 Write Cycle Only 12 TRCSW CS Low to WR Low 10 ns 13 TRWR WR Pulse Width 40 ns 14 TRCHW WR High to CS High 0 ns 15 TRWH WR High to CS Low 40 ns 16 TRWCY WR High to WR Low 40 ns 17 TRDW Data Setup to WR High 15 ns 3 18 TRDHW Data Hold from WR High 15 ns 4 19 TRDWC Data Setup to CS High 15 ns 3 20 TRDHWC Data Hold from CS High 15 ns 4 2 Notes: 1. RD edges may precede or follow CS edges. 2. WR edges may precede or follow CS edges. 3. Either TRDW or TRDWC specification must be met. 4. Either TRDHW or TRDHWC specification must be met. 5. It is not permitted to have both RD and WR low at the same time. IDT™ / ICS™ TOUCH SCREEN CONTROLLER 13 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Register Read Register Write IDT™ / ICS™ TOUCH SCREEN CONTROLLER 14 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Touchscreen Resistance Graph 1 Touchscreen Resistance Graph 2 IDT™ / ICS™ TOUCH SCREEN CONTROLLER 15 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Touchscreen Resistance Graph 3 IDT™ / ICS™ TOUCH SCREEN CONTROLLER 16 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Suggested Layout Notes: 1. The 14.318 MHz input clock on pin 18 should have a 33Ω series termination resistor at its source. Consult ICS for the best way to generate this clock. 2. All digital signals should be kept well away from pins 4, 5, 6, 7, 8, 9, 10, and 11, and any traces connected to those pins. IDT™ / ICS™ TOUCH SCREEN CONTROLLER 17 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Package Outline and Package Dimensions (28-pin SOIC, 300 Mil. Wide Body) Package dimensions are kept current with JEDEC Publication No. 95 28 E Symbol A A1 A2 B C D E e H h L α H INDEX AREA 1 2 D A Millimeters Inches Min Max — 2.65 0.10 — -1.50 0.33 0.51 0.18 0.32 17.70 18.40 7.40 7.60 1.27 Basic 10.00 10.65 0.25 0.75 0.40 1.27 0° 8° Min Max — 0.104 0.004 0.010 0.0040 — 0.013 0.020 0.007 0.013 0.697 0.724 0.291 0.299 .050 Basic 0.394 0.419 0.010 0.029 0.016 0.050 0° 8° h x 45 A1 C - Ce B SEATING PLANE .10 (.004) IDT™ / ICS™ TOUCH SCREEN CONTROLLER C 18 L MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Package Outline and Package Dimensions (28-pin SSOP, 150 Mil. Wide Body) Package dimensions are kept current with JEDEC Publication No. 95 28 E1 Symbol A A1 A2 b C D E E1 e L α E INDEX AREA 1 2 D A 2 Millimeters Inches Min Max 1.35 1.75 0.10 0.25 -1.50 0.20 0.30 0.18 0.25 9.80 10.00 5.80 6.20 3.80 4.00 .635 Basic 0.40 1.27 0° 8° Min Max 0.053 0.069 0.004 0.010 -.059 0.008 0.012 0.007 0.010 0.386 0.394 0.228 0.244 0.150 0.157 .025 Basic 0.016 0.050 0° 8° A A 1 c -Ce b SEATING PLANE L aaa C IDT™ / ICS™ TOUCH SCREEN CONTROLLER 19 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Ordering Information Part / Order Number Marking Shipping Packaging Package Temperature MK712S MK712S Tubes 28-pin SOIC 0 to +70° C MK712STR MK712S Tape and Reel 28-pin SOIC 0 to +70° C MK712SI MK712SI Tubes 28-pin SOIC -30 to +70° C MK712SITR MK712SI Tape and Reel 28-pin SOIC -30 to +70° C MK712R MK712R Tubes 28-pin SSOP 0 to +70° C MK712RTR MK712R Tape and Reel 28-pin SSOP 0 to +70° C MK712RLF MK712RLF Tubes 28-pin SSOP 0 to +70° C MK712RLFTR MK712RLF Tape and Reel 28-pin SSOP 0 to +70° C MK712RI MK712RI Tubes 28-pin SSOP -30 to +70° C MK712RITR MK712RI Tape and Reel 28-pin SSOP -30 to +70° C MK712RWLF MK712RWLF Tubes 28-pin SSOP -35 to +85° C MK712RWLFTR MK712RWLF Tape and Reel 28-pin SSOP -35 to +85° C Parts that are ordered with a “LF” suffix to the part number are the Pb-Free configuration and are RoHS compliant. While the information presented herein has been checked for both accuracy and reliability, Integrated Circuit Systems (ICS) assumes no responsibility for either its use or for the infringement of any patents or other rights of third parties, which would result from its use. No other circuits, patents, or licenses are implied. This product is intended for use in normal commercial applications. Any other applications such as those requiring extended temperature range, high reliability, or other extraordinary environmental requirements are not recommended without additional processing by ICS. ICS reserves the right to change any circuitry or specifications without notice. ICS does not authorize or warrant any ICS product for use in life support devices or critical medical instruments. IDT™ / ICS™ TOUCH SCREEN CONTROLLER 20 MK712 REV L 070805 MK712 TOUCH SCREEN CONTROLLER TOUCH SCREEN CONTROL Innovate with IDT and accelerate your future networks. Contact: www.IDT.com For Sales For Tech Support 800-345-7015 408-284-8200 Fax: 408-284-2775 <product line email> <product line phone> Corporate Headquarters Asia Pacific and Japan Europe Integrated Device Technology, Inc. 6024 Silver Creek Valley Road San Jose, CA 95138 United States 800 345 7015 +408 284 8200 (outside U.S.) Integrated Device Technology Singapore (1997) Pte. Ltd. Reg. No. 199707558G 435 Orchard Road #20-03 Wisma Atria Singapore 238877 +65 6 887 5505 IDT Europe, Limited Prime House Barnett Wood Lane Leatherhead, Surrey United Kingdom KT22 7DE +44 1372 363 339 © 2006 Integrated Device Technology, Inc. All rights reserved. Product specifications subject to change without notice. IDT and the IDT logo are trademarks of Integrated Device Technology, Inc. Accelerated Thinking is a service mark of Integrated Device Technology, Inc. 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