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Electrostatic Sensitive Device!

To prevent equipment damage, use proper grounding techniques.

Electrical Block Diagram

Physical Connector

The Touch Sensor has 8 contact pads and a PCB outline that matches that of a standard 0.3-0.33 mm thick FFC/FPC with 1 mm pitch and top mounted connectors:

The contact pads are placed on the backside of the Touch Sensor PCBA.

List of supported FFC connectors:

Supplier

Part number

Molex

2005290080

Omron Electronic Components

XF3M(1)-0815-1B

Wurth Electronics Inc.

686108148922

Almita Connectors

BL124H-8R-TAND

Pin-Out

Function

Pin name

Pin No

Direction

Description

Comment

Power ground

GND

1

-

Ground


Reset

N_RST

2

Input

Resets sensor to initial state. Active low.

A minimum of a 300 ns low pulse is required

Data Ready

DR

3

Output

Indicates that sensor has data to send

Push/pull output. Only used in I2C mode.

I2C Data

I2C_DATA

4

I/O

I2C data line

Requires external pull-up resistor

I2C Clock

I2C_CLK

5

Input

I2C clock line

Requires external pull-up resistor

USB DM

USB D-

6

I/O

USB DM line

USB 2.0 Compliant

USB DP

USB D+

7

I/O

USB DP line

USB 2.0 Compliant

Power supply

+5V

8

-

+5V power supply

USB 2.0 Compliant

Note: All pins use 3.3V voltage level and have 5V tolerance.

Interface Configuration

The zForce AIR Touch Sensor provides two interfaces for communication with the host system, I2C and USB HID-device. The user can choose to connect one of them, or both. The typical Touch Sensor connection to a host system is shown in the following diagram:

USB Connection

The zForce AIR Touch Sensor provides a USB full-speed device interface through its 8-pin connector. In this connection, PIN 1, 6, 7, 8 ( GND, USB D-, USB D+, VBUS  ) are used. After connecting the sensor to the host system, it could be enumerated as a normal USB HID-device and act as a digitizer for a touch screen.

In this connection, only the default touch active area size could be used. Please refer to Product Variants for the actual values.

In this case, it is recommended to use two 1kΩ pull-up resistors to tie up I2C_DATA and I2C_CLK pins to VBUS or 3.3V power supply to avoid noise issue on I2C interface, and leave other pins as not connected. PIN 2 ( N_RST ) could be used to reset or enable/disable the sensor.

USB Characteristics

The USB interface meets the requirements of USB specifictions 2.0:

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

Input   levels

VDI

Diff.   Input sensitivity


0.2

-

-

V     

VCM

Diff.   common mode range


0.8


2.5

VSE

Single   ended receiver threshold


1.3


2

Output   levels

VOL

Output   level low

1.5kΩ to VDD

-

-

0.3

VOH

Output   level high

15kΩ to VSS

2.8

-

3.6

RPD

D+/D-

VIN=VDD

17

21

24

kΩ  

RPU

D+/D-

VIN=VSS

1.5

1.8

2.1


USB full speed timings: the definitions of data signal rise and fall time are presented in the following table and figure:

Driver characteristcs

Symbol

Parameter

Conditions

Min

Max

tr

Rise time

CL = 50pF

4

20

tf

Fall time

CL = 50pF

4

20

trfm

Rise/fall time matching

tr/tf

90

110

VCRS

Output signal crossover


1.3

2

I2C Connection

The zForce AIR Touch Sensor provides an I2C interface through its 8-pin connector. The interface runs in fast mode, which means the speed is 400kbps. With this interface, more advanced configuration could be performed. PIN 1, 3, 4, 5, 8 ( GND, DR, I2C_DATA, I2C_CLK, VBUS ) are used for this connection. It is recommended to use two 1kΩ pull-up resistors to tie up I2C_DATA and I2C_CLK pins to VBUS or 3.3V power supply to perform proper I2C communication. If USB connection is not used in parallel, PIN 6, 7 ( USB D-, USB D+ ) could be left unconnected.

After the Touch Sensor is powered on, it will act as a slave device on a I2C bus. For further information about what commands could be send or receive through this interface, please refer to I2C Transport.

I2C Characteristics

The I2C interface meets the requirements of the standard I2C communication protocol with the following restrictions: SDA and SCL are mapped to I/O pins that are not “true” open-drain. When configured as open-drain, the PMOS connected between the I/O pin and VDD is disabled, but is still present.

The I2C characteristics are described in the following table:

Symbol

Parameter

Min

Max

Unit

tw(SCLL)

 SCL clock low time

4.7

-

us

tw(SCLH)

 SCL clock high time

4.0

-

tsu(SDA)

 SDA setup time

250

-

ns

th(SDA)

 SDA data hold time

0

-

tr(SDA)

SDA and SCL rise time

-

1000

tr(SCL)

tf(SDA)

SDA and SCL fall time


300

tf(SCL)

th(STA)

 Start condition hold time

4.0

-

us

tsu(STA)

 Repeated Start condition setup time

4.7

-

tsu(STO)

 Stop condition setup time

4.0

-

tw(STO:STA)

 Stop to Start condition time (bus free

4.7

-

tSP

Pulse width of the spikes that are
  suppressed by the analog filter

0

50

ns

Cload

Capacitive load for each bus line

-

400

pF

V IL

Input low level voltage

 

0.8

V

V IH

Input high level voltage

2.3

 

V

V OL

Output low level voltage

 

0.4

V

V OH

Output high level voltage

2.9

 

V

 

PIN 3 ( DR) Characteristics

PIN 3 is used as signal output for DataReady (DR). The DataReady signal is only used in I2C communication.

The sensor can only act as an I2C slave, therefore this pin is needed to notify the host to read the data in the output buffer of the sensor:


  • PIN 3 is set to high (1) when there is data in the buffer to be sent from the sensor.
  • PIN 3 is reset to low (0) when there is no data in the buffer to be sent from the sensor.

PIN 3 can be used as an interrupt input or it can be read repeatedly by the host. When the pin is set to high, the FW will wait for the host to read data from the I2C bus. When the read transaction is finished, this DataReady signal will be reset automatically by the zForce AIR Touch Sensor. The following figure shows the timing behavior of a typical I2C transaction:

I2C Reading Sequence

See I2C Transport.

Power On and Boot Sequence

Power on timing latency are listed in the following table:

NameMinTyp.MaxUnitComment
t1-1520msDelay time from power on to NRST to high voltage.
t2-6070msDelay time from power on to USB pins voltage ready.
t3-170-msDelay time from USB init ready to sending/receiving data.
t45710msDelay time from power on to I2C pins voltage ready.
t5657080msDelay time from I2C pins voltage ready to triggering boot complete packet request.


The power on sequence is shown in the following figure.