IDT MK712 Touch screen controller Datasheet

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
•
•
•
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™ 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 N 051310
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 IDT 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™ TOUCH SCREEN CONTROLLER
2
MK712
REV N 051310
MK712
TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
IC Operation
IDT™ TOUCH SCREEN CONTROLLER
3
MK712
REV N 051310
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™ TOUCH SCREEN CONTROLLER
4
MK712
REV N 051310
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™ TOUCH SCREEN CONTROLLER
5
MK712
REV N 051310
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™ TOUCH SCREEN CONTROLLER
6
MK712
REV N 051310
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™ TOUCH SCREEN CONTROLLER
7
MK712
REV N 051310
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™ TOUCH SCREEN CONTROLLER
8
MK712
REV N 051310
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™ TOUCH SCREEN CONTROLLER
9
MK712
REV N 051310
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 IDT 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™ TOUCH SCREEN CONTROLLER
10
Typ.
MK712
REV N 051310
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™ 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 N 051310
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 IDT 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™ TOUCH SCREEN CONTROLLER
12
MK712
REV N 051310
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™ TOUCH SCREEN CONTROLLER
13
MK712
REV N 051310
MK712
TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
Register Read
Register Write
IDT™ TOUCH SCREEN CONTROLLER
14
MK712
REV N 051310
MK712
TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
Touchscreen Resistance Graph 1
Touchscreen Resistance Graph 2
IDT™ TOUCH SCREEN CONTROLLER
15
MK712
REV N 051310
MK712
TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
Touchscreen Resistance Graph 3
IDT™ TOUCH SCREEN CONTROLLER
16
MK712
REV N 051310
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 IDT 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™ TOUCH SCREEN CONTROLLER
17
MK712
REV N 051310
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™ TOUCH SCREEN CONTROLLER
C
18
L
MK712
REV N 051310
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™ TOUCH SCREEN CONTROLLER
19
MK712
REV N 051310
MK712
TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
Ordering Information
Part / Order Number
Marking
Shipping Packaging
Package
Temperature
MK712SLF
MK712SL
Tubes
28-pin SOIC
0 to +70° C
MK712SLFTR
MK712SL
Tape and Reel
28-pin SOIC
0 to +70° C
MK712SILF
MK712SIL
Tubes
28-pin SOIC
-30 to +70° C
MK712SILFTR
MK712SIL
Tape and Reel
28-pin SOIC
-30 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
MK712RWLF
MK712RWLF
Tubes
28-pin SSOP
-35 to +85° C
MK712RWLFTR
MK712RWLF
Tape and Reel
28-pin SSOP
-35 to +85° C
“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 Device Technology (IDT) 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 IDT. IDT reserves the right to change any circuitry or specifications without notice. IDT
does not authorize or warrant any IDT product for use in life support devices or critical medical instruments.
IDT™ TOUCH SCREEN CONTROLLER
20
MK712
REV N 051310
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
www.idt.com/go/clockhelp
Corporate Headquarters
Integrated Device Technology, Inc.
www.idt.com
© 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