AT42QT4120 - Summary

Features
• QField™ Touchscreen:
– Up to 3.4 inches diagonal screen size supported
• Technology:
– Patented spread-spectrum charge-transfer (transverse mode)
• Panel Materials:
•
•
•
•
•
•
•
•
•
– Plastic, glass, composites, painted surfaces (low particle density metallic paints
possible)
Adjacent Metal:
– Compatible with grounded metal immediately next to sensing channels
Panel Thickness:
– 1 to 2 mm glass, 0.5 to 1.5 mm plastic
Interface:
– I2C-compatible slave mode, 100 kHz or 400 kHz
Moisture Tolerance:
– Best in class
Power:
– 1.8V to 5.5V (2.5V to 5.5V in high speed mode)
Packages:
– 32-pin 5 x 5 mm MLF RoHS compliant
Signal Processing:
– Self-calibration, auto drift compensation, noise filtering
Applications:
– Mobile electronics, terminals, appliances
Patents:
– QMatrix™ (patented Charge-transfer method)
– QField (patented Charge-transfer method, patent-pending QField optimized for
one-layer sensor element designs)
QField™ 10-bit
Touchscreen
Sensor IC
AT42QT4120
Summary
1. Pin-out and Pin Listing Descriptions
1.1
Device Pin-out
N/C
Y2B
N/C
SDA
Vss
Vdd
N/C
SCL
Vdd
RST
Y0A
Y1A
Y2A
N/C
CHANGE
Vss
1
2
32 31 30 29 28 27 26 25
24
23
3
4
5
22
21
20
6
7
8
AT42QT4120
19
18
17
9 10 11 12 13 14 15 16
Y1B
Y0B
A0
Vss
Vdd
Vdd
Vdd
N/C
Note: This is a summary document. A
complete document is available under
NDA. For more information contact
www.atmel.com/touchscreen.
N/C
X3
X2
X1
X0
SMP
VREF
Vss
9506AS–AT42–10/08
1.2
Pin Listing Description
Table 1-1.
Pin Listing
Pin
Name
Type
Comments
If Unused, connect To...
1
N/C
O
Not connected
Leave open
2
CHANGE
OD
State change notification
Leave open
3
Vss
P
Supply ground
–
4
Vdd
P
Power
–
5
Vss
P
Supply ground
–
6
Vdd
P
Power
–
7
N/C
O
Not connected
Leave open
8
N/C
O
Not connected
Leave open
9
Vss
P
Supply ground
–
10
VREF
I
Supply ground
–
11
SMP
O
Sample output
–
12
X0
O
X matrix drive line
Leave open
13
X1
O
X matrix drive line
Leave open
14
X2
O
X matrix drive line
Leave open
15
X3
O
X matrix drive line
Leave open
16
N/C
O
Not connected
Leave open
17
N/C
O
Not connected
Leave open
18
Vdd
P
Power
–
19
Vdd
P
Power
–
20
Vdd
P
Power
–
21
Vss
P
Supply ground
–
22
A0
I
I C-compatible address select
–
23
Y0B
I/O
Y line connection
Leave open
24
Y1B
I/O
Y line connection
Leave open
25
Y2B
I/O
Y line connection
Leave open
26
N/C
O
Not connected
Leave open
27
SDA
OD
Serial Interface Data
–
28
SCL
OD
Serial Interface Clock
–
29
RST
I
Reset low; has internal 30k - 60k pull-up
Leave open or Vdd
30
Y0A
O
Y line connection
Leave open
31
Y1A
O
Y line connection
Leave open
32
Y2A
O
Y line connection
Leave open
I
O
OD
2
2
Input only
Output only, push-pull
Open drain output
I/O
X
P
Input and output
Clock resonator
Ground or power
AT42QT4120
9506AS–AT42–10/08
AT42QT4120
1.3
Wiring Diagram
Figure 1-1.
Wiring Diagram
VDD
Vunreg
follow regulator manufacturer's recommended values for input
and output bypass capacitors; keep output capacitor close to
pins 4 and 6. If not possible, add a 100nF capacitor next to those pins.
VREG
N/C
VDD
N/C
N/C
N/C
QT4120
2
I C-COMPATIBLE
SDA
N/C
N/C
Rx3
SCL
Rx2
Rx1
VDD
Rx0
Ry0
Rc
CHANGE
CHANGE
Cs0
Ry1
Cs1
Ry2
I2C-COMPATIBLE
ADDRESS SELECT
MATRIX X DRIVE
Rp
MATRIX Y SCAN IN
Rp
Cs2
NOTES:
Rs2
Rs1
Rs0
1) The central pad on the underside of the chip
is a Vss pin and should be connected to ground.
Do not put any other tracks underneath
the body of the chip.
2) It is important to place all Cs, Rs, Rx and Ry
components physically near to the chip.
Suggested regulator manufacturers:
• Torex (XC6215 series)
• Seiko (S817 series)
• BCDSemi (AP2121 series)
3
9506AS–AT42–10/08
2. Overview
The AT42QT4120 (QT4120) QField IC is a self-contained capacitive touchscreen controller that
employs Atmel’s patented transverse charge-transfer (QT™) acquisition method. The controller
senses changes in electrical charge forced across two electrode elements by a pulse edge (see
Figure 2-1).
Figure 2-1.
Field Flow Between X and Y Elements
overlying panel
X
eleme nt
Y
elem ent
The touchscreen is critical to the design and is specially patterned to improve linearity, limit hand
shadow and keep the number of connection lines to a minimum.
The device includes all signal processing functions necessary to provide stable sensing under a
wide variety of changing conditions. Only a few external parts are required for operation. The
entire circuit can be built within a few square centimeters of single-sided PCB area. CEM-1 and
FR1 punched, single-sided materials can be used for the lowest possible cost. The PCB’s rear
can be mounted flush on the back of a glass or plastic panel using a conventional adhesive,
such as 3M VHB two-sided adhesive acrylic film.
The device uses an I2C-compatible interface to allow channel data to be extracted and to permit
touchscreen parameter setup. The command structure is designed to minimize the amount of
data traffic while maximizing the amount of information conveyed.
In addition to normal operating and setup functions the device can also report back actual signal
strengths.
4
AT42QT4120
9506AS–AT42–10/08
AT42QT4120
3. Revision History
Revision No.
History
Revision AS – October 2008
Initial release for chip revision 7.0
5
9506AS–AT42–10/08
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9506AS–AT42–10/08
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