NXP Semiconductors OM11058 User manual

UM10720
User manual for the TFT touch demo board OM11058
Rev. 1 — 25 June 2013 User manual
Document information
Info Content
Keywords OM11058, PCA8885, PCF8885, capacitive touch sensor, touch on TFT,
touch foil
Abstract The OM11058 demonstrates the capabilities of the PCA8885 and
PCF8885 for touch on display by using a double-sided ITO touch foil with
a diamond matrix and two ICs cascaded for an 8 8 resolution on a 7 inch
TFT display

UM10720 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 1 — 25 June 2013 2 of 16
Contact information
For more information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: [email protected]
NXP Semiconductors UM10720
User manual for the TFT touch demo board OM11058
Revision history
Rev Date Description
v.1 20130625 new user manual, first revision

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User manual Rev. 1 — 25 June 2013 3 of 16
NXP Semiconductors UM10720
User manual for the TFT touch demo board OM11058
1. Introduction
Interactive user interfaces like in smartphones have become a must also in automotive,
industrial and white goods control units.
Unlike smartphones where multi-touch, drag and drop and zooming features are used, the
dedicated user interfaces in, for instance climate control or washing machine, only have to
be a replacement of mechanical buttons by on-display touch buttons. Accordingly, the
hardware- and software-design should be as simple as possible.
The PCA8885 and PCF8885 are providing very suitable features for easy configuration,
connection of various numbers of channels, optimization of sensitivity and sampling for
each application.
The purpose of the OM11058 is to demonstrate the capabilities of the PCA8885 and
PCF8885 for touch displays.
1.1 The PCA8885 and PCF8885 multi-channel capacitive proximity
sensors
The PCA8885 and PCF8885 are capacitive 8-channel touch and proximity sensors
detecting changes in capacitance on remote sensing plates. Changes in the static
capacitances (as opposed to dynamic capacitance changes) are automatically
Fig 1. OM11058 demo board

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User manual Rev. 1 — 25 June 2013 4 of 16
NXP Semiconductors UM10720
User manual for the TFT touch demo board OM11058
compensated using continuous auto-calibration. Remote sensing plates (for example,
conductive foils) can be connected to the IC. The eight input channels operate
independently of each other. There is also a built-in option for a matrix arrangement of the
sensors: interrupts are generated only when two channels are activated simultaneously,
suppression of additional channel outputs when two channels are already active.
Key features of the PCA8885 and PCF8885 are:
•Eight independent channels (can be configured as 4 4 matrix)
•I2C-bus interface
•One subaddress to enable up to 64 keys, cascading 2 devices
•Sleep mode, activated via I2C-bus or external input
•Three sensing modes: one key, two keys and n-keys
•Two event handling modes: direct and latching mode
•Adjustable scan frequency
•Channel masking feature
•Fast start-up mode
•Operating temperature range (Tamb = 40 C to +85 C)
•TSSOP28 and SO28 package available
•PCA8885: AEC-Q100 compliant for automotive and harsh environment applications
Fig 2. Block diagram of PCA8885 and PCF8885
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UM10720 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 1 — 25 June 2013 5 of 16
NXP Semiconductors UM10720
User manual for the TFT touch demo board OM11058
2. Description and technology of OM11058
The OM11058 block diagram is shown in Figure 3.
Fig 3. Block diagram of the OM11058
LPC1788
Developmentkit
7” TFTdisplay
13 x 21 linediamond
structure on two
layers
OM11056
2 x PCA8885evaluation board
Interconnection board for FPC
UM10720_01

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NXP Semiconductors UM10720
User manual for the TFT touch demo board OM11058
2.1 Display layers
The basic building elements of - for example - a passive LCD are shown in Figure 4.
The touch sensor pads can be placed on the same layer as the display ITO as an
interleaved pattern (in-cell) or on top of the display glass, sandwiched under the polarizer
(on-cell), see Figure 5.
Fig 4. LCD layers
incident light
Segments:
Segments – Top ITO
Liquidcrystal molecules
Polarizer
Displayglass-Top
Common–Bottom ITO
Polarizer
transparent opaque
UM10720_03

UM10720 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 1 — 25 June 2013 7 of 16
NXP Semiconductors UM10720
User manual for the TFT touch demo board OM11058
The features of an in-cell stack are:
•Segment and touch ITO patterns are made in the same process step
•Lower LCD module cost
•Limited number of touch buttons can be made
For the OM11058, a separate foil with top and bottom ITO layers is used.
2.2 Touch panel
For the touch layer on the TFT display in the OM11058, a separate double sided touch foil
with 21 13 diamond matrix structure was taken as an off-the-shelf product.
a. On-cell touch stack b. In-cell touch stack
Fig 5. Touch display technology
Glass
ITO Layer Touch
Polarizer
ITO Layer
Segment
LiquidCrystal
UM10720_04
Glass
Polarizer
ITO Layer
Segment+Touch
LiquidCrystal
UM10720_05
Available vertical and horizontal lines:
13 21 = 273 points resolution 8 8 lines provide 64 touch buttons of which 16 are used for the OM11058
Fig 6. 7- inch touch panel
76543210
0
1
2
3
4
5
6
7
IC#2
IC#1

UM10720 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 1 — 25 June 2013 8 of 16
NXP Semiconductors UM10720
User manual for the TFT touch demo board OM11058
If the sensor pads are organized in a matrix layout such as a foil with horizontally
connected diamond pads on one side and vertically connected diamond pads on the other
side, the sensor inputs of a single IC can be used for a 4 4 matrix as shown in Figure 7.
For larger matrices two PCA8885 packages can be cascaded as shown in Figure 8 to
locate the XY position of a touch.
Fig 7. 4 4 matrix layout
Bottomlayer Toplayer
+

UM10720_08

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NXP Semiconductors UM10720
User manual for the TFT touch demo board OM11058
Fig 8. Cascaded application diagram
IN[0]
IN[1]
IN[2]
IN[3]
IN[7]
VDD
VDD(INTREGD)
100 nF
TEST
VSS
CPC[0] CPC[7]
SCL
SDA
CLK_IN
INT_IN
CLK_OUT
INT
A0
SLEEP
PCA8885
IN[0]
IN[1]
IN[2]
IN[3]
IN[7]
VDD
VDD(INTREGD)
100 nF
TEST
VSS
CPC[0] CPC[7]
SCL
SDA
CLK_IN
INT_IN
CLK_OUT
INT
A0
SLEEP
PCA8885
SENSOR MATRIX
(primary)
(secondary)
VDD
RPU
100 nF
RPU
to MCU
VDD
100 nF
VDD
100 nF
CCPC[0]
100 nF
CCPC[7]
100 nF
CCPC[0]
100 nF
CCPC[7]
(1)
(1)
(3)
013aaa581
(2)

UM10720 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 1 — 25 June 2013 10 of 16
NXP Semiconductors UM10720
User manual for the TFT touch demo board OM11058
3. Quick start
3.1 Power supply
•The OM11058 is shipped with a USB cable. The USB supply port should be able to
source 2.5 A. Using the USB connector is also the option giving the highest sensitivity.
•Alternatively aAC/DC power adapter (5 V, >2.5 A) can be used. Preferably the power
adapter should be a linear converter. If a switching mode AC/DC converter (SMPS) is
used, it should be a three-pin connector with protective earth.
The supply connectors of the OM11058 are shown in Figure 9.
3.2 Operation
•When powering up, it takes about 30 seconds to get the touch operational due to the
delays in the start of the MCU evaluation board in order to get right sequence of
interrupts and I2C communication.
•All buttons are implemented as single switches.
CAUTION
This device needs a USB source that is able to handle 2.5 A. Ensure that the USB supply
connection is able to provide this amount of power. Otherwise, damages may occur.
Fig 9. Supply connectors
USB or power jack for
supply connecon