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DATASHEET
TOUCH SCREEN CONTROLLER Description
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. The IC continually monitors the screen waiting for a touch. In this mode, the supply current is typically 0.5A. 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.
MK712 Features
* Packaged in 28-pin SSOP (150 mil) or 28-pin SOIC (300
mil)
* Industrial (-30C to +70C) and commercial (0 to +70C)
and automotive (-35C to +85C) temperature ranges
Block Diagram
* * * * * * * * * * * * * * * * *
Available in Pb (lead) free Fully integrated, lowest power solution Low standby current of 0.5A (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
NC INT TOUCH VDD VDD XH XL YH YL GND GND WR RD CS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 D0 D1 D2 D3 D4 D5 VDD GND D6 D7 CLKIN A0 A1 A2
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MK712 TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
Pin Descriptions
Pin Number
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
Pin Name
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
Pin Type
-- 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
Pin Description
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.
IDTTM / ICSTM TOUCH SCREEN CONTROLLER
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MK712
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MK712 TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
IC Operation
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MK712
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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:
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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.
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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.
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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 3A. If the input clock is stopped, the supply current is also less than 3A. 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.
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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.
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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.
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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
Supply Voltage, VDD (referenced to ground) All Inputs and Outputs (referenced to ground) Ambient Operating Temperature (commercial) Ambient Operating Temperature (industrial) Ambient Operating Temperature (automotive) Storage Temperature Junction Temperature Soldering Temperature (10 to 20 seconds max) 7V
Rating
-0.5 V to VDD+0.5 V 0 to +70 C -30 to +70 C -35 to +85 C -65 to +150 C 125 C 260 C
Recommended Operation Conditions
Parameter
Ambient Operating Temperature (commercial) Ambient Operating Temperature (industrial) Ambient Operating Temperature (automotive) Power Supply Voltage (measured in respect to GND) (commercial and industrial) Power Supply Voltage (measured in respect to GND) (automotive)
Min.
0 -30 -35 +3.0 +3.135
Typ.
Max.
+70 +70 +85 +5.5 +5.5
Units
C C C V V
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DC Electrical Characteristics
Unless stated otherwise,VDD = 3.3 V or 5V, TA = 0 to +70 C (commercial), -30C to +70C (industrial), -35C to +85C (automotive)
Parameter
Operating Voltage Operating Voltage Input High Voltage Input Low Voltage Output High Voltage Output High Voltage Output Low Voltage Input High Voltage Input Low Voltage Output High Voltage Output Low Voltage Operating Supply Current
Symbol
VDD VDD VIH VIL VOH VOH VOL VIH VIL VOH VOL IDD
Conditions
Commercial and industrial Automotive VDD=5 V VDD=5 V IOH = -2 mA VDD=5 V, IOH = -12 mA VDD=5 V, IOL = 12 mA VDD=3.3 V VDD=3.3 V VDD=3.3 V, IOH = -8 mA VDD=3.3 V, IOL = 8 mA At VDD=5 V, 300 screen, 100 PPS At VDD=3.3 V, Note 3 Standby, Clock, Note 4 Standby, Note 5 Power down, PD=0 or PD=1, no clock
Min.
3.0 3.135 2
Typ.
Max.
5.5 5.5 0.8
Units
V V V V V V
VDD-0.4 2.4 0.4 1.9 0.4 2.4 0.4 5 3 0.5 0.5 0.2 50 7 3 3 3
V V V V V mA mA A A A mA pF
Short Circuit Current Input Capacitance
IOS CIN
Each output
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AC Electrical Characteristics
Unless stated otherwise,VDD = 3.3 V or 5 V, TA = 0 to +70 C (commercial), -30C to +70C (industrial), -35C to +85C (automotive)
Parameter
Input Clock Frequency, pin 18 Input Clock Duty Cycle, pin 18 Output Rise Time Output Fall Time Resolution Non-linearity Touch Screen Resistance
Symbol
Conditions
Note 1 At 1.5 V
Min.
12 25
Typ.
14.32
Max.
20 75 3 3 12 2
Units
MHz % ns ns bits LSB
tOR tOF
0.8 to 2.0 V, VDD=5 V 2.0 to 0.8 V, VDD=5 V Monotonic, Note 2 100
2000
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, 300 screen, 100 PPS. Note 4: Assumes no 14.3 MHz input clock overshoot, no touch. Note 5: With no touch, no clock.
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Register Interface Timing
Number
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 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.
Symbol
TRASC TRAHC TRCCY TRSCR TRRD TRCHR1 TRCHR2 TRDC TRDR TRDHC TRDHR TRCSW TRWR TRCHW TRWH TRWCY TRDW TRDHW TRDWC
Description
Address Setup to CS Low Address Hold from CS High CS High to CS Low CS Low to RD Low RD Pulse Width RD High to CS High RD High to CS Low CS Low to Data RD Low to Data CS High to Data Release RD High to Data Release CS Low to WR Low WR Pulse Width WR High to CS High WR High to CS Low WR High to WR Low Data Setup to WR High Data Hold from WR High Data Setup to CS High
Min.
5 0 40 10 40 0 40
Max.
Units
ns ns ns ns ns ns ns
Note
Read and Write Cycles
Read Cycle Only
35 35 2 2 10 40 0 40 40 15 15 15 15 20 20
ns ns ns ns ns ns ns ns ns ns ns ns ns 3 4 3 4 2 1 1
Write Cycle Only
TRDHWC Data Hold from CS High
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Register Read
Register Write
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Touchscreen Resistance Graph 1
Touchscreen Resistance Graph 2
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Touchscreen Resistance Graph 3
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Suggested Layout
Notes: 1. The 14.318 MHz input clock on pin 18 should have a 33 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.
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Package Outline and Package Dimensions (28-pin SOIC, 300 Mil. Wide Body)
Package dimensions are kept current with JEDEC Publication No. 95
28
Millimeters Symbol A A1 A2 B C D E e H h L
h x 45
Inches 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
E INDEX AREA
H
12 D
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
A A1
C
- Ce
B SEATING PLANE
.10 (.004)
C
L
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Package Outline and Package Dimensions (28-pin SSOP, 150 Mil. Wide Body)
Package dimensions are kept current with JEDEC Publication No. 95
28
Millimeters Symbol A A1 A2 b C D E E1 e L 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
Inches 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
E1 INDEX AREA
E
12 D
A 2 A 1
A
c
-Ce
b SEATING PLANE L
aaa C
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Ordering Information
Part / Order Number
MK712S MK712STR MK712SI MK712SITR MK712R MK712RTR MK712RLF MK712RLFTR MK712RI MK712RITR MK712RWLF MK712RWLFTR
Marking
MK712S MK712S MK712SI MK712SI MK712R MK712R MK712RLF MK712RLF MK712RI MK712RI MK712RWLF MK712RWLF
Shipping Packaging
Tubes Tape and Reel Tubes Tape and Reel Tubes Tape and Reel Tubes Tape and Reel Tubes Tape and Reel Tubes Tape and Reel
Package
28-pin SOIC 28-pin SOIC 28-pin SOIC 28-pin SOIC 28-pin SSOP 28-pin SSOP 28-pin SSOP 28-pin SSOP 28-pin SSOP 28-pin SSOP 28-pin SSOP 28-pin SSOP
Temperature
0 to +70 C 0 to +70 C -30 to +70 C -30 to +70 C 0 to +70 C 0 to +70 C 0 to +70 C 0 to +70 C -30 to +70 C -30 to +70 C -35 to +85 C -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.
IDTTM / ICSTM TOUCH SCREEN CONTROLLER
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MK712
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MK712 TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
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(c) 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. All other brands, product names and marks are or may be trademarks or registered trademarks used to identify products or services of their respective owners. Printed in USA

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