SX8648I05AULTRT - Semtech - Datasheet.Live

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SX8648

Ultra Low Power, Capacitive Button and Slider

Touch Controller (8 sensors) with Enhanced LED Drivers

GENERAL DESCRIPTION

The SX 8648 is an ultra lo w power, full y integr ated 8-

channel solution for capacitive touch-buttons and

slider applications. Unlike many capacitive touch

solutions, the SX8648 features dedicated capacitive

sense inputs (that requires no external components)

in addition to 8 general purpose I/O ports (GPIO).

Each GPIO is typicall y conf igured as LED dri ver with

independent PWM source for enhanced lighting

control such as intensity and fading.

The SX 8648 i nclu des a c a pac it iv e 1 0 b it ADC an alo g

interface with automatic compensation up to 100pF.

The high resolution capacitive sensing supports a

wide variety of touch pad sizes and shapes and

allows capacitive buttons to be created using thick

overlay materials (up to 5mm) for an extremely

robust and ESD immune system design.

The SX8648 incorporates a versatile firmware that

was specially designed to simplify capacitive touch

solution design and offers reduced time-to-market.

Integrated multi-time programmable memory

provides the ultimate flexibility to modify key firmware

parameters (gain, threshold, scan period, auto offset

compensation… ) in the field without the need for

new firmware development.

The SX8648 supports the 400 kHz I²C serial bus

data protocol and includes a field programmable

slave a ddress. The ti ny 4mm x 4mm footprint m akes

it an ideal solution for portable, battery powered

applications where power and density are at a

premium.

TYPIC AL APPLIC ATION CIRCUIT

KEY PRODUCT FEATURES

 Complete Eight Sensors Capacitive Touch Controller for

Buttons and Slider

 Pre-configured for 2 Buttons and a Slider

 8 LED Drivers with Individual Intensity, Fading Control

and Autolight Mode

 256 steps PWM Linear and Logarithmic control

 High Resolution Capacitive Sensing

 Up to 100pF of Offset Capacitance Compensation at

Full Sensitivity

 Capable of Sensing through Overlay Materials up to

5mm thick

 Extremely Low Power Optimized for Portable Application

 8uA (typ) in Sleep Mode

 80uA (typ) in Doze Mode (Scanning Period 195ms)

 175uA (typ) in Active Mode (Scanning Period 30ms)

 Programmable Scanning Period from 15ms to 1500ms

 Auto Offset Compensation

 Eliminates False Triggers due to Environmental

Factors (Temperature, Humidity)

 Initiated on Power-up and Configurable Intervals

 Multi-Time In-Field Programmable Firmware Parameters

for Ultimate Flexibility

 On-chip user programmable memory for fast, self

contained start-up

 "Smart" Wake-up Sequence for Easy Activation from Doze

 No External Components per Sensor Input

 Internal Clock Requires No External Components

 Differential Sensor Sampling for Reduced EMI

 400 KHz Fast-Mode I²C Interface with Interrupt

 -40°C to +85°C Operation

APPLICATIONS

 Notebook/Netbook/Portable/Handheld computers

 Cell phones, PDAs

 Consumer Products, Instrumentation, Automotive

 Mechanical Button Replacement

ORDERING INFORMATION

Part Number Temperature

Range Package

SX8648I05AULTRT1 -40°C to +85°C Lead Free MLPQ-UT28

1 3000 Units/reel

* This device is RoHS/WEEE compliant and Halogen Free

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SX8648

Ultra Low Power, Capacitive Button and Slider

Touch Controller (8 sensors) with Enhanced LED Drivers

Table of Contents

GENERAL DESCRIPTION........................................................................................................................1

TYPIC AL APPLIC ATION CIRCUIT............................................................................................................1

KEY PRODUCT FEATURES.....................................................................................................................1

APPLICATIONS.......................................................................................................................................1

ORDERING INFORMATION......................................................................................................................1

1 GENERAL DESCRIPTION...............................................................................................................4

1.1 Pin Diagram 4

1.2 Marking information 4

1.3 Pin Description 5

1.4 Simplified Block Diag ram 6

1.5 Acronyms 6

2 ELECTRICAL CHARACTERISTICS .................................................................................................7

2.1 Absolute Maximum Ratings 7

2.2 Recommended Operating Conditions 7

2.3 Thermal Characteristics 7

2.4 Electrical Specifications 8

3 FUNCTIONAL DESCRIPTION........................................................................................................10

3.1 Quickst art Application 10

3.2 Introduction 10

3.2.1 General 10

3.2.2 GPIOs 11

3.2.3 Parameters 11

3.2.4 Configuration 11

3.3 Scan Pe rio d 12

3.4 Operation modes 12

3.5 Sensors on the PCB 14

3.6 Button and Slider Information 15

3.6.1 Button Information 15

3.6.2 Slider Information 15

3.7 Analog Sensing Interface 17

3.8 Offset Compensation 18

3.9 Processing 19

3.10 Configuration 19

3.11 Power Management 21

3.12 Clock Circuitry 21

3.13 I2C interface 21

3.14 Reset 22

3.14.1 Power up 22

3.14.2 RESETB 22

3.14.3 Software Reset 23

3.15 Interrupt 24

3.15.1 Power up 24

3.15.2 Assertion 24

3.15.3 Clearing 24

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3.15.4 Example 25

3.16 General Purpose Input and Outputs 25

3.16.1 Introduction and Definitions 25

3.16.2 GPI 26

3.16.3 GPP 26

3.16.4 GPO 27

3.16.5 Intensity index vs PWM pulse width 30

3.17 Smart Wake Up 31

4 PIN DESCRIPTIONS.....................................................................................................................32

4.1 Introduction 32

4.2 ASI pins 32

4.3 Host interface pins 33

4.4 Power management pins 36

4.5 General purpose IO pins 37

5 DETAILED CONFIGURATION DESCRIPTIONS ..............................................................................38

5.1 Introduction 38

5.2 General Parameters 41

5.3 Capacitiv e Sen sors Para met ers 42

5.4 Button Parameters 47

5.5 Slider Parameters 51

5.6 Mapping Parameters 55

5.7 GPIO Parameters 58

6 I2C INTERFACE...........................................................................................................................62

6.1 I2C Write 62

6.2 I2C read 63

6.3 I2C Registers Overview 64

6.4 Status Registers 65

6.5 Control Registers 68

6.6 SPM Gateway Registers 70

6.6.1 SPM Write Sequence 71

6.6.2 SPM Read Sequence 72

6.7 NVM burn 73

7 APPLIC ATION INFORMATION......................................................................................................74

8 PACKAGING INFORMATION ........................................................................................................75

8.1 Package Outline Drawing 75

8.2 Land Pattern 75

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SX8648

Ultra Low Power, Capacitive Button and Slider

Touch Controller (8 sensors) with Enhanced LED Drivers

1 GENERAL DESCRIPTION

1.1 Pin Diagram

SX8648

Top View

8 9 10 11 12 13 14

22232425262728

bottom gr ound pad

cap2

cap3

cap4

cap5

cap6

cap7

gnd

gpio5

gpio4

gpio3

gpio2

gpio1

gnd

gpio0

cap1

cap0

vana

resetb

gnd

gpio7

vdig

gpio6

vdd

scl

intb

sda

Figure 1 Pinout Diagram

1.2 Marking information

8648

yyww

xxxxx

R05

yyww = Date Code

xxxxx = Semtech lot number

R05 = Semtech Code

Figure 2 Marking Inform ation

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Ultra Low Power, Capacitive Button and Slider

Touch Controller (8 sensors) with Enhanced LED Drivers

1.3 Pin Description

Number Name Type Description

1 CAP1 Analog Capacitive Sensor 1

2 CAP2 Analog Capacitive Sensor 2

3 CAP3 Analog Capacitive Sensor 3

4 CAP4 Analog Capacitive Sensor 4

5 CAP5 Analog Capacitive Sensor 5

6 CAP6 Analog Capacitive Sensor 6

7 CAP7 Analog Capacitive Sensor 7

8 CN Analog Integration Capacitor, negative terminal (1nF between CN and CP)

9 CP Analog Integration Capacitor, positive terminal (1nF between CN and CP)

10 VDD Power Main input power supply

11 INTB Digital Output Interrupt, active LOW, requires pull up resistor (on host or external)

12 SCL Digital Input I2C Clock, requires pull up resistor (on host or external)

13 SDA Digital Input/Output I2C Data, requires pull up resistor (on host or external)

14 GPIO0 Digital Input/Output General Purpose Input/Output 0

15 GPIO1 Digital Input/Output General Purpose Input/Output 1

16 GND Ground Ground

17 GPIO2 Digital Input/Output General Purpose Input/Output 2

18 GPIO3 Digital Input/Output General Purpose Input/Output 3

19 GPIO4 Digital Input/Output General Purpose Input/Output 4

20 GPIO5 Digital Input/Output General Purpose Input/Output 5

21 GND Ground Ground

22 GPIO6 Digital Input/Output General Purpose Input/Output 6

23 GPIO7 Digital Input/Output General Purpose Input/Output 7

24 VDIG Analog Digital Core Decoupling, connect to a 100nF decoupling capacitor

25 GND Ground Ground

26 RESETB Digital Input Active Low Reset. Connect to VDD if not used.

27 VANA Analog Analog Core Decoupling, connect to a 100nF decoupling capacitor

28 CAP0 Analog Capacitive Sensor 0

bottom plate GND Ground Exposed pad connec t to ground

Table 1 P in descr ipt ion

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Ultra Low Power, Capacitive Button and Slider

Touch Controller (8 sensors) with Enhanced LED Drivers

1.4 Simplified Block Diagram

The simplified block diagram of the SX8648 is illustrated in Figure 3.

vana

resetb

gnd

gpo7

vdig

gpo6

vdd

scl

intb

sda

Figure 3 Simplified block diagram of the SX8648

1.5 Acronyms

ASI Analog Sensor Interface

DCV Digital Compensation Value

GPI General Purpose Input

GPO General Purpose Output

GPP General Purpose PWM

MTP Multiple Time Programmable

NVM Non Volatile Memor y

PWM Pulse Width Modulation

QSM Quick Start Memory

SPM Shadow Parameter Memory

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2 ELECTRICAL CHARACTERISTICS

2.1 Absolute Maximum Ratings

Stresses above the values listed in “Absolute Maximum Ratings” may cause permanent damage to the device.

This is a stress rating only and functional operation of the device at these, or any other conditions beyond the “Recommended

Operating Conditions”, is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device

reliability.

Parameter Symbol Min. Max. Unit

Supply Voltage VDD -0.5 3.9 V

Input voltage (non-supply pins) VIN -0.5 3.9 V

Input current (non-supply pins) IIN 10 mA

Operating Junction Temperature TJCT 125 °C

Reflow temperature TRE 260 °C

Storage temperature TSTOR -50 150 °C

ESD HBM (Human Body model)(i) ESDHBM 3 kV

Latchup(ii) I

LU ± 100 mA

Table 2 Absolute Maximum Ratings

(i) Tested to JEDEC standard JESD22-A114

(ii) Tested to JEDEC standard JESD78

2.2 Recommended Operating Conditions

Parameter Symbol Min. Max. Unit

Supply Voltage VDD 2.7V 3.6 V

Supply Voltage Drop(iii, iv, v) VDDdrop 100 mV

Supply Voltage for NVM programming VDD 3.0V 3.6 V

Ambient Temperature Range TA -40 85 °C

Table 3 Recom m ended Oper ating Conditions

(iii) Performance for 2.6V < VDD < 2.7V might be degraded.

(iv) Operation is not guaranteed below 2.6V. Should VDD briefly drop below this minimum value, then the SX8648 may

require;

- a hardware reset issued by the host using the RESETB pin

- a software reset issued by the host using the I2C interface

(v) In the event the host processor is reset or undergoes a power OFF/ON cycle, it is recommended that the host also resets

the SX8648 and assures that parameters are re-written into the SPM (should these differ to the parameters held in NVM).

2.3 Thermal Characteristics

Parameter Symbol Min. Max. Unit

Thermal Resistance - Junction to Ambient (vi) θJA 25 °C/W

Table 4 Ther m al Char acteristics

(vi) Static airflow

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Ultra Low Power, Capacitive Button and Slider

Touch Controller (8 sensors) with Enhanced LED Drivers

2.4 Electrical Specifications

All values are valid within the operating conditions unless otherwise specified.

Parameter Symbol Conditions Min. Typ. Max. Unit

Current consumption

Active mode, average IOP,active 30ms scan period,

8 sensors enabled,

minimum sensitivity

175

225 uA

Doze mode, average IOP,Doze 195ms scan period,

8 sensors enabled,

minimum sensitivity

110 uA

Sleep IOP,sleep I2C and GPI listening,

sensors disabled 8 17 uA

GPIO, set as Input, RESETB, SCL, SDA

Input logic high VIH 0.7*VDD VDD + 0.3V V

Input logic low VIL VSS applied to GND pins VSS - 0.3V 0.8 V

Input leakage current LI CMOS input ±1 uA

Pull up resistor RPU when enabled 660 kΩ

Pull down resistor RPD when enabled 660 kΩ

GPIO set as Output, INTB, SDA

Output logic high VOH I

OH <4mA VDD-0.4 V

Output logic low VOL I

OL,GPIO<12mA

IOL,SDA,INTB<4mA 0.4 V

Start-up

Power up time tpor time between rising edge

VDD and rising INTB 150 ms

RESETB

Pulse width tres 50 ns

External components

Capacitor between VDIG, GND Cvdig type 0402, tolerance +/-50% 100 nF

Capacitor between VANA, GND Cvana type 0402, tolerance +/-50% 100 nF

Capacitor between CP, CN Cint type 0402, tolerance +/-10% 1 nF

Capacitor between VDD, GND Cvdd type 0402, tolerance +/-50% 100 nF

Table 5 E lect rical Specifications

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SX8648

Ultra Low Power, Capacitive Button and Slider

Touch Controller (8 sensors) with Enhanced LED Drivers

Parameter Symbol Conditions Min. Typ. Max. Unit

I2C Timing Specifications (i)

SCL clock frequency fSCL 400 KHz

SCL low period tLOW 1.3 us

SCL high period tHIGH 0.6 us

Data setup time tSU;DAT 100 ns

Data hold time tHD;DAT 0 ns

Repeated start setup time tSU;STA 0.6 us

Start condition hold time tHD;STA 0.6 us

Stop condition setup time tSU;STO 0.6 us

Bus free time between stop and start t

BUF 500 us

Input glitch sup pre ssi on tSP 50 ns

Table 6 I 2C Tim ing Specification

Notes:

(i) All timing specifications, Figure 4 and Figure 5, refer to voltage levels (VIL, VIH, VOL) defined in Table 5.

The interface complies with slave F/S mode as described by NXP: “I2C-bus specification, Rev. 03 - 19 June 2007”

Figure 4 I2C Start and Stop tim ing

Figure 5 I2C Data timing

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Ultra Low Power, Capacitive Button and Slider

Touch Controller (8 sensors) with Enhanced LED Drivers

3 FUNCTIONAL DESCRIPTION

3.1 Quickstart Application

The SX8648 is preconfigured (Quickstart Application) for an application with 2 buttons, a slider (consisting of 6

sensors) and 8 LED drivers using logarithmic PWM fading.

Implem enting a schem atic based on Fig ure 6 will be imm ediately oper ational after powering without progra mming

the SX8648 (e ven wit hout hos t).

HOST

SX8648 gnd

gpio5

gpio4

gpio3

gpio2

gpio1

gnd

gpio0

vana

resetb

gnd

gpio7

vdig

gpio6

vdd

scl

intb

sda

analog

sensor

interface

micro

processor

RAM

ROM

NVM

I2C

GPIO

controller

power management

clock

generation

PWM

LED

controller

bottom plate

cap2

cap3

cap4

cap5

cap6

cap7

cap0

cap1

Figure 6 Quickstart Application

Touching the sensor on the CAP0 pin will enable automatically the LED connected to GPIO0. When the CAP0

sensor is released the LED on GPIO0 will slowly fade-out using smooth logarithmic fading.

The sensor CAP1 has its LED associated on pin GPIO1 showing a touch or a release.

The sensors on CAP2 to CAP7 are used in a slider configuration. A finger on the slider will enable the LED on

GPIO2 to GPIO7 indicating the finger slider position.

The sensor detection and the LED fading described above are operational without any host interaction.

This is made possible using the SX8648 Autolight feature described in the following sections.

3.2 Introduction

3.2.1 General

The SX8648 is inten ded to be used in app lications which require capacitive sen sors covered by isolating overlay

material. A finger approaching the capacitive sensors will change the charge that can be loaded on the sensors.

The SX 8648 measur es the c hange of c harge and co nv erts that int o d igi tal val ues (tic ks). T he lar ger the charge on

the sensors , the larger the number of ticks will be. T he charge to tick s conversion is don e by the SX864 8 Analog

Sensor Interface (ASI).

The ticks are further processed by the SX8648 and converted in a high level, easy to use information for the

user’s host.

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The information between SX8648 and the user’s host is passed through the I2C interface with an additional

interrupt signal indicat ing that the SX8648 has new information. For buttons this inf ormation is sim ply touched or

released.

3.2.2 GPIOs

A second path of feedback to the user is using General Purpose Input Output (GPIO) pins. The SX8648 offers

eight individual configurable GPIO pins. The GPIO can e.g. be set as a LED driver which slowly fade-in when a

finger touches a button and slowly fade-out when the button is released. Fading intensity variations can be

logarithmic or linear. Interval speed and initial and final light intensity can be selected by the user. The fading is

done using a 256 steps PWM. The SX8648 has eight individual PWM generators, one for each GPIO pin.

The LED fading can be initiated automatically by the SX8648 by setting the SX8648 Autolight feature. A simple

touch on a sensor and the corresponding LED will fade-in without any host interaction over the I2C.

In case the A utolight f eat ure is dis abled t hen th e hos t wil l decid e to s tart a LE D fadi ng-in p eriod, s im ply b y setting

the GP0 pin to ‘high’ using one I2C command. The SX8648 will then slowly fade-in the LED using the PWM

autonomously.

In case th e host needs to have f ull contr ol of the LED intensi ty the n the hos t can set the G PIO i n GPP m ode. T he

host is then able to set the PWM pulse width freely at the expense of an increased I2C occupation.

The GPIOs can be set further in the digital standard Input mode (GPI).

3.2.3 Parameters

The SX8648 has m any low level built-in, fixed algorithms and procedures. To allow a lot of freedom for the user

and adapt the SX8648 for different applications these algorithms and procedures can be configured with a large

set of parameters which will be described in the following sections. Examples of parameters are which sensors

are buttons or which sensors are parts of a slider, which GPIO is used for outputs or LEDs and which GPIO is

mapped to which butt on.

Sensitivity and detection thresholds of the sensors are part of these parameters. Assuming that overlay material

and sensors areas are identical then the sensitivities and thresholds will be the same for each sensor. In case

sensors are not of the same size then sensitivities or thresholds might be chosen individually per sensor.

So a smaller size sensor can have a larger sensitivity while a big size sensor may have the lower sensitivity.

3.2.4 Configuration

During a development phase the parameters can be determined and fine tuned by the users and downloaded

over the I2C in a dynamic way. The parameter set can be downloaded over the I2C by the host each time the

SX8648 boots up. This allows a flexible way of setting the parameters at the expense of I2C occupation.

In case the parameters are frozen they can be programmed in Multiple Time Programmable (MTP) Non Volatile

Memory (NVM) on the SX8648. The programming needs to be done once (over the I2C). The SX8648 will then

boot up from the NVM and additional parameters from the host are not required anymore.

In case the host desires to over write the boot-up NVM param eters (partly or even complete) this can be done b y

additional I2C communications.

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3.3 Scan Period

The basic operation Scan period of the SX8648 sensing interface can be split into three periods over time.

In the first period (Sensing) the SX8648 is sensing all enabled CAP inputs, from CAP0 towards CAP7.

In the sec o nd peri od ( Process ing) t he SX 86 48 pr ocesses the sensor d ata, ver ifie s and up dat es th e G PIO a n d I2 C

status registers.

In the third period (Timer) the SX8648 is set in a low power mode and waits until a new cycle starts.

Figure 7 shows the different SX8648 periods over time.

Figure 7 Scan Period

The s can peri od det erm ines the m inim um reaction tim e of th e SX 8648. T he s can per iod can be c onf igure d by t he

host from 15ms to values larger than a second.

The reaction time is defined as the interval between a touch on the sensor and the moment that the SX8648

generates the interrupt on the INTB pin. The shorter the scan period the faster the reaction time will be.

Very low po wer c ons umptio n c an be obt ai ned by sett in g very lo ng sc an p er io ds with th e expense of ha vi ng lo nger

reaction times.

Important: All external e ve nts like GPIO, I2C and INTB are upd ate d i n th e pr oce s s ing per iod , s o o nc e e very s can

period. If e.g. a GPI would change sta te direct ly after t he processin g period t hen this will be report ed with a d elay

of one scan period later in time.

3.4 Operation modes

The SX 8648 has 3 op eratio n m odes. T he main dif f erenc e is f ound in t he re action t im e (c orres ponding to t he s can

period) and power consumption.

Active mode offers fast scan periods. The typical reaction time is 30ms. All enabled sensors are scanned and

information data is processed within this interval.

Doze mode increases the scan period time which increases the reaction time to 195ms typical and at the same

time reduces the operating current.

Sleep mode turns the SX8648 OFF, except for the I2C and GPI peripheral, minimizing operating current while

maintaining the power supplies. In Sleep mode the SX8648 does not do any sensor scanning.

The user can specify other scan periods for the Active and Doze mode and decide for other compromises

between reaction time and power consumption.

In mos t applicati ons the re action t ime needs to be fas t when fing ers ar e present, but can be sl ow whe n no pers on

uses the application. In case the SX8648 is not used for a specific time it can go from Active mode into Doze

mode and p ower wi ll be sa ved. T his tim e-out is det erm ined by the Pas sive T imer which c an be c onfigur ed b y the

user or turned OFF if not required.

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To leave Doze mode and enter Active mode this can be done by a simple touch on any button.

For some applications a single button touch might cause undesired wakening up and Active mode would be

entered too often.

The SX8648 offers therefore a smart wake-up sequence feature in which the user needs to touch and release a

correct sequence of buttons before Active m ode will be entered. T his is explained in m ore detail in the W ake-Up

Sequence section.

The host can decide to force the operating mode by issuing commands over the I2C (using register

CompOpMode) and take fully control of the SX8648.

The diagram in Figure 8 shows the available operation modes and the possible transitions.

Figure 8 Operation modes

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3.5 Sensors on the PCB

The capacitive sensors are relativel y sim ple copper areas on the PCB connected to the eight SX8648 capacitive

sensor input pins (CAP0…CAP7).The sensors are covered by isolating overlay material (typically 1mm...3mm).

The area of a sensor is typicall y on e square cent imeter which c orresponds about to th e area of a fin ger touc hing

the overlay material.

The capacitive sensors can be setup as ON/OFF buttons (see example Figure 9) or arranged in a slider

configuration (see example Figure 10) for e.g. menu scrolling or volume control applications.

Figure 9 PCB top layer of four sensors for buttons (surrounded by a ground plane)

Figure 10 PCB top layer of one slider using six sensors (surrounded by ground plane)

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3.6 Button and Slider Information

3.6.1 Button Information

The buttons have two simple states (see Figure 11): ON (touched by finger) and OFF (released and no finger

press).

Figure 11 Buttons

A finger is detected as soon as the number of ticks from the ASI reaches a user-defined threshold plus a

hysteresis.

A release is detected if the ticks from the ASI go below the threshold minus a h ysteresis. The hysteresis around

the threshold avoids rapid touch and release signaling during transients.

3.6.2 Slider Information

In case s ensors are ar ranged i n a sl ider c onfigur atio n the O N, OFF inf orm ation rem ains availab le as if it would be

a single sensor button.

Figure 12 Slider ON, OFF

Wherever the slider is touched the information will be set to ON. If no finger is present the slider information will be

OFF.

Due to the 2 dimensional character of the slider more information can be derived by processing the ticks.

During a touch a finger will influence most of the time the charge on one or two sensors but never all of the

sensors at the same time. Some sensor ticks will be larger than others based on the finger position.

The processing algorithms can therefore determine where the finger is positioned on the slider.

Interpolation between sensors increases the resolution beyond the number of sensors in the slider.

The interpo lation c an be done a lread y on the PCB s ensor s tructures ( analog, lik e the chevron s lider in F igure 10)

and as well by SX8648 digital processing of the ticks using center of gravity calculations.

The position of the finger on the PCB structures varies between the m inimum zero and a user defin ed maximum

(Figure 13).

....x...

position

min max

Figure 13 Slider Position

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The pos ition belongin g to the m inimum and as sociated to a s ensor is def ined arbitrar ily. The SX 8648 defin es the

minim um pos ition to t he se nsor with the lo west C AP p in index . E. g. if CA P0 is a butto n (or d isabled) a nd C AP1 to

CAP7 are the sensors of the slider then the position ‘zero’ starts at CAP1 and the maximum is found at CAP7.

In addition to the slider position, the SX8648 allows to detect finger movements. The movement occurs if the

finger pos ition changes a certain step size bet ween two succeeding scan period s. A very slow moving finger will

not be considered as a movement as the changing position will be minor. The SX8648 allows detecting a move

low (direction max to min) (see Figure 14) and a move high (direction min to max) (see Figure 15).

min max

Figure 14 Slider Move Low

Figure 15 Slider Move High

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3.7 Analog Sensing Interface

The Analog Sensing Interface (ASI) converts the charge on the sensors into ticks which will be further digitally

process ed. T he basic pr inci ple of the ASI will be expla i ned in this sect ion.

The ASI c onsists of a multiplexer s electing t he sensor, analog switc hes, a ref erence volt age, an ADC sigm a delta

converter, an offset compensation DAC and an external integration capacitor (see Figure 16).

switches

cap2

cap1

cap0 analog

multi-

plexor

Offset

compensation

DAC

ADC ticks (raw)

compensation DCV

ASI processing

Cint

voltage

reference

low pass

ticks-diff

ticks-ave

cap7

Figure 16 Analog Sensor Interface

To get the ticks representing the charge on a specific sensor the ASI will execute several steps.

The c harge on a s ensor c ap (e.g. C AP0) will be acc um ulated multip le tim es on the ex terna l integratio n capac itor,

Cint.

This results in an increasing voltage on Cint proportional to the capacitance on CAP0.

At this stage the offset compensation DAC is enabled. The compensation DAC generates a voltage proportional

to an estimation of the external capacitance. The estimation is obtained by the offset compensation procedure

executed e.g. at power-u p.

The difference between the DAC output and the charge on Cint is the desired signal. In the ideal case the

diff erence of char ge will be c onverted t o zero tic k s if no finger is present and the num ber of tick s becom es high in

case a finger is present.

The difference of charge on Cint and the DAC output will be transferred to the ADC (Sigma Delta Integrator).

After the charge transfer to the ADC the steps above will be repeated.

The larger the number the cycles are repeated the larger the signal out of the ADC with improved SNR. The

sensitivity is therefore directly related to the number of cycles.

The SX8648 allows setting the sensitivity for each sensor individually in applications which have a variety of

sensors sizes or diff erent overl ays or f or f ine-tunin g perf orm ances . The optim al sensitivi ty is de pending he avil y on

the final app licat ion . If the sens itiv it y is too low the tick s will not pass the thres holds and it is not p oss ible to detect

fingers. In case the sensi tivit y is set too large a f inger hov ering abov e the sensor s will alrea dy be detected bef ore

the finger really touches the overlay resulting in false detections.

Once the ASI has finished the first sensor, the ticks are stored and the ASI will start measuring the next sensor

until all (enabled) sensors pins have been treated.

In case some sensors are disabled then these result in lower power consumption simply because the ASI is active

for a shorter period and the following processing period will be shorter.

The ticks from the ASI will then be handled by the digital processing.

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3.8 Offset Compensation

The capacitance at the CAP pins is determined by an intrinsic capacitance of the integrated circuit, the PCB

traces, gr ound c ou pl ing an d the s ens or pl anes . This c apacitance is rel ati ve ly large and might become eas il y som e

tens of pF. This parasitic capacitance will vary only slowly over time due to environmental changes.

A finger touch is in the order of one pF. If the finger approaches the sensor this occurs typically fast.

The ASI has the difficult task to detect and distinguish a small, fast changing capacitance, from a large, slow

varying c apacitanc e. This woul d require a very precis e, high res olution AD C and com plicated, po wer consu ming,

digital processing.

The SX 8648 featur es a 16 bit DAC which c ompens ates f or the larg e, slow varyin g capacita nce alrea dy in f ront of

the ADC. In other words the ADC converts only the desired small signal. In the ideal world the ADC will put out

zero ticks even if the external capacitance is as high as 100pF.

At each power-up of the SX8648 the Digital Com pensation Values (DC V) are es timated by th e digital pr ocessing

algorithms. The algorithm will adjust the compensation values such that zero ticks will be generated by the ADC.

Once the correct compensation values are found these will be stored and used to compensate each CAP pin.

If the SX86 48 is s hut down the c ompens ation values will b e lost. At a n ext powe r-up the pr ocedure s tarts all o ver

again. T his assures th at the SX8648 will operate u nder an y con dition. Po weri ng up at e.g. d ifferent tem peratures

will not change the performance of the SX8648 and the host does not have to do anything special.

The DCVs do not need to be updated if the external conditions remain stable.

However if e.g. temperature changes this will influence the external capacitance. The ADC ticks will drift then

slowly around zero values basically because of the mismatch of the compensation circuitry and the external

capacitance.

In case the average value of the ticks become higher than the positive noise threshold (configurable by user) or

lower than the negative threshold (configurable by user) then the SX8648 will initiate a compensation procedure

and find a new set of DCVs.

Compensation procedures can as well be initiated by the SX8648 on periodic intervals. Even if the ticks remain

within the positive and negative noise thresholds the compensation procedure will then estimate new sets of

DCVs.

Finall y the h os t c an ini tia te a c ompensation procedure b y using the I2C int er f ac e ( in Acti ve or Do ze mode). This is

e.g. required after the host changed the sensitivity of sensors.

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3.9 Processing

The f irst pr ocessing st ep of the ra w tick s, com ing out of the ASI, is low p ass f iltering to o bta in an estim ation of the

average capacitance: tick-ave (see Figure 17).

This slowly varying average is important in the detection of slowly changing environmental changes.

ticks (raw)

compen sat io n DCV

ASI processing

low pass

tick-diff

tick-ave

processing

GPIO

controller

PWM LED

controller

I2C

SPM

Figure 17 Processing

The difference of the tick average and the raw ticks, tick-diff, is a good estimation of rapid changing input

capacitances.

The tic k - diff , tick-ave and the c onf ig ur ati on parameter s in t he SP M ar e th en proc ess ed an d d eter mines the sens or

information, I2C registers status and PWM control.

3.10 Configuration

Figure 18 shows the building blocks used for configuring the SX8648.

Figure 18 Configuration

The default configuration parameters of the SX8648 are stored in the Quick Start Memory (QSM). This

configur ation data is setu p to a ver y com mon applicat ion for the SX864 8 with 6 buttons a nd a slider. W ithout any

programming or host interaction the SX8648 will startup in the Quick Start Application.

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The QSM settings are fixed and can not be changed by the user.

In case the application needs different settings than the QSM settings then the SX8648 can be setup and/or

programmed over the I2C interface.

The configuration parameters of the SX8648 can be stored in the Multiple Time Programmable (MTP) Non

Volatile Memory (NVM). The NVM contains all those parameters that are defined and stable for the application.

Examples are the number of sensors enabled, sensitivity, active and Doze scan period. The details of these

parameters are described in the next chapters.

At power up the SX8648 checks if the NVM contains valid data. In that case the configuration parameter source

becom es the NV M. If the NVM is em pt y or non- valid t h en the co nf iguration sourc e bec om es the QS M. In t he nex t

step the SX8648 copies the configur ation parameter source (QSM or N VM) into the Shadow Param eter Memory

(SPM). The SX8648 is operational and uses the configuration parameters of the SPM.

During p o wer do wn or r eset event th e SP M l oses a ll conte nt. I t will a utomatic all y be re loa ded ( f r om QSM or NVM)

following power up or at the end of the reset event.

The host will interface with the SX8648 through the I2C bus.

The I2C of the SX8648 consists of 16 registers. Some of these I2C registers are used to read the status and

inform ation of the button an d the slider . Other I2 C regis ters allo w the host to t ak e control of the SX 8648. T he host

can e.g. decide to change the operation mode from Active mode to Doze mode or go into Sleep (according to

Figure 8).

Two additional modes allow the host to have an access to the SPM or indirect access to the NVM.

These modes are required during development, can be used in real time or in-field programming.

Figure 19 shows the Host SPM mode. In this mode the host can decide to overwrite the SPM. This is useful

during the d ev elo pment phases of the applicati on wher e the conf igur at io n par ameters ar e not yet full y def ine d and

as well during the operation of the application if some parameters need to be changed dynamically.

Figure 19 Host SPM mode

The c ontent of the S PM re mains valid as lon g as the SX864 8 is po wer ed a nd no res et is perform ed. Af ter a po wer

down or reset the host needs to re-write the SPM if relevant for the application.

Figure 20 shows the Host NVM mode. In this mode the host will be able to write the NVM.

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Figure 20 Host NVM mode

The writing of the host towards the NVM is not done directly but done in 2 steps (Figure 20).

In the first step the host writes to the SPM (as in Figure 19). In the second step the host signals the SX8648 to

copy the SPM content into the NVM.

Initially the NVM memory is empty and it is required to determine a valid parameter set for the application. This

can be done during the development phase using dedicated evaluation hardware representing the final

application. This development phase uses probably initially the host SPM mode which allows faster iterations.

Once the p arameter set is determ ined this c an be writ ten to the NVM over the I2 C using the 2 steps appr oach by

the host or a dedicated programmer for large volumes production (as described in the paragraphs 6.6 and 6.7).

3.11 Power Management

The SX8648 uses on-chip voltage regulators which ar e controlled by the on-chip m icroprocessor. The regulators

need to be stabilized with an external capacitor between VANA and ground and between VDIG and ground (see

Table 5). Both regulators are designed to only drive the SX8648 internal circuitry and must not be loaded

externally.

3.12 Clock Circuitry

The SX8648 has its own internal clock generation circuitry that does not require any external components. The

clock circuitry is optimized for low power operation and is controlled by the on-chip microprocessor. The typical

operating frequency of the oscillating core is 16.7MHz from which all other lower frequencies are derived.

3.13 I2C interface

The I2C interface allows the communication between the host and the SX8648.

The I2C slave implemented on the SX8648 is compliant with the standard (100kb/s) and fast mode (400kb/s)

The default SX8648 I2C address equals 0b010 1011.

A different I2C address can be programmed by the user in the NVM.

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3.14 Reset

The reset can be performed by 3 sources:

- power up,

- RESETB pin,

- software reset.

3.14.1 Power up

During power up the INTB is kept low. Once the power up sequence is terminated the INTB is released

autonomously. The SX8648 is then ready for operation.

Figure 21 Power Up vs. INTB

During the po wer on p erio d the SX 8 648 s ta bi li zes th e i nternal reg ula tors , RC c loc k s and the f irmware in it ial i zes all

registers.

During the power up the SX8648 is not accessible and I2C communications are forbidden.

As soon as the INTB rises the SX8648 will be ready for I2C communication.

3.14.2 RESETB

When RESETB is driven low the SX8648 will reset and start the power up sequence as soon as RESETB is

driven high or pulled high.

In case the user does not require a hardware reset control pin then the RESETB pin can be connected to VDD.

Figure 22 Har dware Reset

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3.14.3 Software Reset

To perform a software reset the host needs to write 0xDE followed by 0x00 at the SoftReset register at address

0xB1.

Figure 23 Software Reset

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3.15 Interrupt

3.15.1 Power up

During power up the INTB is kept low. Once the power up sequence is terminated the INTB is released

autonomously. The SX8648 is then ready for operation.

Figure 24 Power Up vs. INTB

During the po wer on p erio d the SX 8 648 s ta bi li zes th e i nternal reg ula tors , RC c loc k s and the f irmware in it ial i zes all

registers.

During the power up the SX8648 is not accessible and I2C communications are forbidden.

As soon as the INTB rises the SX8648 will be ready for I2C communication.

3.15.2 Assertion

INTB is updated in Active or Doze mode once every scan period.

The INTB will be asserted: at the following events:

• if a Button e vent oc curr ed (touch or r elease if enab led) . I2C regis ters Cap StatMs b and Ca pStatLs b sho w the

detailed status of the Buttons,

• if a Slider event occurred (touch, release, move high, move low or position change). I2C registers

CapStatMsb, SldPosMsb and SldPosLsb show the detailed status of the Slider,

• if a GPI edge occur red (rising or f alling if enabled). I2C r egister Gpi Stat shows t he detailed stat us of the GPI

pins,

• when actually entering Active or Doze mode either through automatic wakeup or via host request (may be

delayed by 1 scan period). I2C register CompOpmode shows the current operation mode,

• once compensation procedure is completed either through automatic trigger or via host request (may be

delayed by 1 scan period),

• once SPM write is effective (may be delayed by 1 scan period),

• once NVM burn procedure is completed (may be delayed by 1 scan period),

• during reset (power up, hardware RESETB, software reset).

3.15.3 Clearing

INTB is updated in Active or Doze mode once every scan period.

The clearing of the INTB is done as soon as the host performs a read to the IrqSrc I2C register or reset is

completed

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3.15.4 Example

A typical example of the assertion and clearing of the INTB and the I2C communication is shown in Figure 25.

Figure 25 Interrupt and I2C

When a button is touched the SX8648 will assert the interrupt (1). The host will read the IrqSrc information over

the I2C and this clears the interrupt (2).

If the f inger releas es the bu tton the inter ru pt will be as serted ( 3). The host r eading the IrqSr c inf orm ation will clear

the interrupt (4).

In case the host does not react to an interrupt this results in a missing touch.

3.16 General Purpose Input and Outputs

3.16.1 Introduction and Definitions

The SX 8648 of f er s eight Genera l P ur pose Inp ut a nd Outputs (G PIO) p ins whic h c an be c o nf igured in any of these

modes:

- GPI (General Purpose Input)

- GPP (General Purpose PWM)

- GPO (General Purpose Output)

Each of these modes is described in more details in the following sections.

The polarit y of the GPP and GPO pins is def ined as in figure below, dr iving an LED as exam ple. It has to be set

accordingly in SPM parameter GpioPolarity.

Figure 26 Polarit y definition, (a) norma l, (b) inverted

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The PWM blocks used in GPP and GPO modes are 8-bits based and clocked at 2MHz typ. hence offering 256

selectable pulse width values with a granularity of 128us typ.

Figure 27 PWM definition, (a) small pulse width, (b) large pulse width

3.16.2 GPI

GPIOs configured as GPI will operate as digital inputs with standard low and high logic levels.

Optional pull-up/down and debounce can be enabled. Each GPI is individually edge programmable for INTB

generation which will also exit Sleep/Doze mode if relevant.

SPM/I2C parameters applicable in GPI mode are listed in table below. Please refer to the relevant SPM/I2C

parameters sections for more details.

GPI

GpioMode X

GpioPullUpDown X

GpioInterrupt X

SPM

GpioDebounce X

IrqSrc[4] X

I2C GpiStat X

Table 7 SPM/I2C Parameters Applicable in GPI Mode

3.16.3 GPP

GPIOs configured as GPP will operate as PWM outputs directly controlled by the host. A typical application is

LED dimming.

Typical GPP operation is illustrated in figure below.

Figure 28 LED contro l in GPP mode

SPM/I2C parameters applicable in GPP mode are listed in table below. Please refer to the relevant SPM/I2C

parameters sections for more details.

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GPP

GpioMode X

GpioOutPwrUp X1

GpioPolarity X

GpioIntensityOn X1

GpioIntensityOff X1

SPM

GpioFunction X

GppPinId X

I2C GppIntensity X1

1 At power up, GppIntensit y of each GPP pin is initialized with GpioIntens ityOn or Gpi oInt ensityOff depending on GpioOutPwrUp

corresponding bits val ue.

Table 8 SPM/ I 2C Parameters Applicable in GPP Mode

3.16.4 GPO

GPIOs configured as GPO will operate as digital outputs which can generate both standard low/high logic levels

and PWM low/high duty cycles levels. Ty pical application is LED ON/OFF control.

Transitions between ON and OFF states can be triggered either automatically in Autolight mode or manually by

the host. This is illustrated in figures below.

Figure 29 LED Contr ol in GPO mode, Autolight OFF

Figure 30 LED Contr ol in GPO mode, Autolight ON (mapped to Button)

Addition ally these tra nsitions c an be conf igured to be done with or without f ading f ollowing a logarithmic or linear

function. This is illustrated in figures below.

Figure 31 GPO ON transition (LED fade in), normal polarity, (a) linear, (b) logarithmic

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Figure 32 GPO ON transition (L ED f ade in), inverted polarit y, (a) linear, (b) logarithmic

The fading o ut (e.g. af ter a button is releas ed) is identi cal to the f ading in bu t an addit ional of f dela y can be a dded

before the fading starts (Figure 33 and Figure 34).

Figure 33 GPO OFF transition ( L ED fade out), normal polarity, (a) linear, (b) logarit hmic

Figure 34 GPO OFF transition ( LED fade out), invert ed polarit y, (a) linear, (b) logarithmic

Please n ote tha t stan dard hig h/lo w log ic sig nals ar e ju st a spec ific case of GPO m ode and can also b e ge nerated

simply by setting inc/dec time to 0 (ie OFF) and programming intensity OFF/ON to 0x00 and 0xFF.

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SPM/I2C parameters applicable in GPO mode are listed in table below.

GPO

GpioMode X

GpioOutPwrUp X1

GpioAutoligth X

GpioPolarity X

GpioIntensityOn X

GpioIntensityOff X

GpioFunction X

GpioIncFactor X

GpioDecFactor X

GpioIncTime X

GpioDecTime X

SPM

GpioOffDelay X

I2C GpoCtrl X2

1 Only if Autolight is OFF, else must be left to 0 (default value)

2 Only if Autolight is OFF, else ignored

Table 9 SPM/I2C Parameters Applicable in GPO Mode

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3.16.5 Intensity index vs PWM pulse width

Tables below are used to convert all intensity indexes parameters GpioIntensityOff, GpioIntensityOn and

GppIntensity but also to generate fading in GPO mode

During fading in(out), the index is automatically incremented(decremented) at every Inc(Dec)Time x

Inc(Dec)Factor until it reaches the programmed GpioIntensityOn(Off) value.

Index Lin/Log Index Lin/Log Index Lin/Log Index Lin/Log Index Lin/Log Index Lin/Log Index Lin/Log Index Lin/Log

0 0/0 32 33/5 64 65/12 96 97/26 128 129/48 160 161/81 192 193/125 224 225/184

1 2/0 33 34/5 65 66/13 97 98/27 129 130/49 161 162/82 193 194/127 225 226/186

2 3/0 34 35/5 66 67/13 98 99/27 130 131/50 162 163/83 194 195/129 226 227/188

3 4/0 35 36/5 67 68/13 99 100/28 131 132/51 163 164/84 195 196/130 227 228/190

4 5/0 36 37/5 68 69/14 100 101/29 132 133/52 164 165/86 196 197/132 228 229/192

5 6/2 37 38/6 69 70/14 101 102/29 133 134/53 165 166/87 197 198/133 229 230/194

6 7/2 38 39/6 70 71/14 102 103/30 134 135/54 166 167/88 198 199/135 230 231/197

7 8/2 39 40/6 71 72/15 103 104/30 135 136/55 167 168/89 199 200/137 231 232/199

8 9/2 40 41/6 72 73/15 104 105/31 136 137/55 168 169/91 200 201/139 232 233/201

9 10/2 41 42/6 73 74/15 105 106/32 137 138/56 169 170/92 201 202/140 233 234/203

10 11/2 42 43/7 74 75/16 106 107/32 138 139/57 170 171/93 202 203/142 234 235/205

11 12/2 43 44/7 75 76/16 107 108/33 139 140/58 171 172/95 203 204/144 235 236/208

12 13/2 44 45/7 76 77/16 108 109/33 140 141/59 172 173/96 204 205/146 236 237/210

13 14/2 45 46/7 77 78/17 109 110/34 141 142/60 173 174/97 205 206/147 237 238/212

14 15/3 46 47/7 78 79/17 110 111/35 142 143/61 174 175/99 206 207/149 238 239/215

15 16/3 47 48/8 79 80/18 111 112/35 143 144/62 175 176/100 207 208/151 239 240/217

16 17/3 48 49/8 80 81/18 112 113/36 144 145/63 176 177/101 208 209/153 240 241/219

17 18/3 49 50/8 81 82/19 113 114/37 145 146/64 177 178/103 209 210/155 241 242/221

18 19/3 50 51/8 82 83/19 114 115/38 146 147/65 178 179/104 210 211/156 242 243/224

19 20/3 51 52/9 83 84/20 115 116/38 147 148/66 179 180/106 211 212/158 243 244/226

20 21/3 52 53/9 84 85/20 116 117/39 148 149/67 180 181/107 212 213/160 244 245/229

21 22/3 53 54/9 85 86/21 117 118/40 149 150/68 181 182/109 213 214/162 245 246/231

22 23/3 54 55/9 86 87/21 118 119/40 150 151/69 182 183/110 214 215/164 246 247/233

23 24/4 55 56/10 87 88/22 119 120/41 151 152/71 183 184/111 215 216/166 247 248/236

24 25/4 56 57/10 88 89/22 120 121/42 152 153/72 184 185/113 216 217/168 248 249/238

25 26/4 57 58/10 89 90/23 121 122/43 153 154/73 185 186/114 217 218/170 249 250/241

26 27/4 58 59/10 90 91/23 122 123/44 154 155/74 186 187/116 218 219/172 250 251/243

27 28/4 59 60/11 91 92/24 123 124/44 155 156/75 187 188/117 219 220/174 251 252/246

28 29/4 60 61/11 92 93/24 124 125/45 156 157/76 188 189/119 220 221/176 252 253/248

29 30/4 61 62/11 93 94/25 125 126/46 157 158/77 189 190/121 221 222/178 253 254/251

30 31/4 62 63/12 94 95/25 126 127/47 158 159/78 190 191/122 222 223/180 254 255/253

31 32/5 63 64/12 95 96/26 127 128/48 159 160/80 191 192/124 223 224/182 255 256/256

Table 10 Intensity index vs. PWM pulse widt h (normal polar ity)

Index Lin/Log Index Lin/Log Index Lin/Log Index Lin/Log Index Lin/Log Index Lin/Log Index Lin/Log Index Lin/Log

0 256/256 32 224/251 64 192/244 96 160/230 128 128/208 160 96/175 192 64/131 224 32/72

1 255/256 33 223/251 65 191/243 97 159/229 129 127/207 161 95/174 193 63/129 225 31/70

2 254/256 34 222/251 66 190/243 98 158/229 130 126/206 162 94/173 194 62/127 226 30/68

3 253/256 35 221/251 67 189/243 99 157/228 131 125/205 163 93/172 195 61/126 227 29/66

4 252/256 36 220/251 68 188/242 100 156/227 132 124/204 164 92/170 196 60/124 228 28/64

5 251/254 37 219/250 69 187/242 101 155/227 133 123/203 165 91/169 197 59/123 229 27/62

6 250/254 38 218/250 70 186/242 102 154/226 134 122/202 166 90/168 198 58/121 230 26/59

7 249/254 39 217/250 71 185/241 103 153/226 135 121/201 167 89/167 199 57/119 231 25/57

8 248/254 40 216/250 72 184/241 104 152/225 136 120/201 168 88/165 200 56/117 232 24/55

9 247/254 41 215/250 73 183/241 105 151/224 137 119/200 169 87/164 201 55/116 233 23/53

10 246/254 42 214/249 74 182/240 106 150/224 138 118/199 170 86/163 202 54/114 234 22/50

11 245/254 43 213/249 75 181/240 107 149/223 139 117/198 171 85/161 203 53/112 235 21/48

12 244/254 44 212/249 76 180/240 108 148/223 140 116/197 172 84/160 204 52/110 236 20/46

13 243/254 45 211/249 77 179/239 109 147/222 141 115/196 173 83/159 205 51/109 237 19/44

14 242/253 46 210/249 78 178/239 110 146/221 142 114/195 174 82/157 206 50/107 238 18/41

15 241/253 47 209/248 79 177/238 111 145/221 143 113/194 175 81/156 207 49/105 239 17/39

16 240/253 48 208/248 80 176/238 112 144/220 144 112/193 176 80/155 208 48/103 240 16/37

17 239/253 49 207/248 81 175/237 113 143/219 145 111/192 177 79/153 209 47/101 241 15/35

18 238/253 50 206/248 82 174/237 114 142/218 146 110/191 178 78/152 210 46/100 242 14/32

19 237/253 51 205/247 83 173/236 115 141/218 147 109/190 179 77/150 211 45/98 243 13/30

20 236/253 52 204/247 84 172/236 116 140/217 148 108/189 180 76/149 212 44/96 244 12/27

21 235/253 53 203/247 85 171/235 117 139/216 149 107/188 181 75/147 213 43/94 245 11/25

22 234/253 54 202/247 86 170/235 118 138/216 150 106/187 182 74/146 214 42/92 246 10/23

23 233/252 55 201/246 87 169/234 119 137/215 151 105/185 183 73/145 215 41/90 247 9/20

24 232/252 56 200/246 88 168/234 120 136/214 152 104/184 184 72/143 216 40/88 248 8/18

25 231/252 57 199/246 89 167/233 121 135/213 153 103/183 185 71/142 217 39/86 249 7/15

26 230/252 58 198/246 90 166/233 122 134/212 154 102/182 186 70/140 218 38/84 250 6/13

27 229/252 59 197/245 91 165/232 123 133/212 155 101/181 187 69/139 219 37/82 251 5/10

28 228/252 60 196/245 92 164/232 124 132/211 156 100/180 188 68/137 220 36/80 252 4/8

29 227/252 61 195/245 93 163/231 125 131/210 157 99/179 189 67/135 221 35/78 253 3/5

30 226/252 62 194/244 94 162/231 126 130/209 158 98/178 190 66/134 222 34/76 254 2/3

31 225/251 63 193/244 95 161/230 127 129/208 159 97/176 191 65/132 223 33/74 255 0/0

Table 11 I nt ensity index vs. PWM pulse width (inverted polarity)

Recommended/default settings are inverted polarity (to take advantage from high sink current capability) and

logarithmic mode (due to the non-linear response of the human eye).

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3.17 Smart Wake Up

The SX8648 offers a smart wake up mechanism which allows waking-up from the Doze low power mode to the

Active mode in a secure/controlled way and not by any unintentional sensor activation.

Until the f ull correct wake-up seque nce is entere d, the SX864 8 will rem ain in Doze m ode. Any wron g key implies

the whole sequence to be entered again.

A sequence of up to 6 keys can be defined. Each key must be followed by a release to be validated.

The smart wake-up mechanism can also be disabled which implies that Doze mode can hence only be exited

from GPI or I2C command.

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4 PIN DESCRIPTIONS

4.1 Introduction

This chapter describes briefly the pins of the SX8648, the way the pins are protected, if the pins are analog,

digital, require pull up or pull down resistors and show control signals if these are available.

4.2 ASI pins

CAP0, CAP1, ..., CAP7

The capacitance sensor pins (CAP0, CAP1, ..., CAP7) are connected directly to the ASI circuitry which converts

the sensed capacitance into digital values.

The capacitance sensor pins which are not used should be left open.

The enabled CAP pins need be connected directly to the sensors without significant resistance (typical below

some ohms, connection vias are allowed).

The capacitance sensor pins are protected to VANA and GROUND.

Figure 35 shows the simplified diagram of the CAP0, CAP1, ..., CAP7 pins.

SX8648

sensor ASI CAPx CAP_INx

VANA

Note : x = 0, 1,2,…7

Figure 35 Simplif ied diagr am of CAP0, CAP1, ..., CAP7

CN, CP

The CN and the C P pins ar e connecte d to the AS I circ uitry. A 1nF s am pling c apacitor between C P and CN n eeds

to be placed as close as possible to the SX8648.

The CN and CP are protected to VANA and GROUND.

Figure 36 shows the simplified diagram of the CN and CP pins.

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SX8648

ASI

VANA

Figure 36 Simplified diagram of CN and CP

4.3 Host interface pins

The host interface consists of the interrupt pin INTB, a reset pin RESETB and the standard I2C pins: SCL and

SDA.

INTB

The INTB pin is an open drain output that requires an external pull-up resistor (1..10 kOhm). The INTB pin is

protected to VDD using dedicated devices. The INTB pin has diode protected to GROUND.

Figure 37 shows a simplified diagram of the INTB pin.

VDD

R_INT

INTB

SX8648

INT

to host

Figure 37 Simplified diagram of INTB

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SCL

The SCL pi n is a h igh impedance in put pin. The SCL pin is pr o tec ted to V DD, using dedic a ted de v ice s, i n or d er to

conform to standard I2C slave specifications. The SCL pin has diode protected to GROUND.

An external pull-up resistor (1..10 kOhm) is required on this pin.

Figure 38 shows the simplified diagram of the SCL pin.

VDD

R_SCL

SCL

SX8648

from host

SCL_IN

Figure 38 Simplified diagram of SCL

SDA

SDA is an IO pin that can be used as an open drain output pin with external pull-up resistor or as a high

impedance input pin. The SDA IO pin is protected to VDD, using dedicated devices, in order to conform to

standard I2C slave specifications. The SDA pin has diode protected to GROUND.

An external pull-up resistor (1..10 kOhm) is required on this pin.

Figure 39 shows the simplified diagram of the SDA pin.

VDD

R_SDA

SDA

SX8648

SDA_OUT

from/to host

SDA_IN

Figure 39 Simplified diagram of SDA

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RESETB

The RESETB pin is a high impedance input pin. The RESETB pin is protected to VDD using dedicated devices.

The RESETB pin has diode protected to GROUND.

Figure 40 shows the simplified diagram of the RESETB pin controlled by the host.

VDD

R_RESETB

RESETB

SX8648

from host

RESETB_IN

Figure 40 Simplified diagr am of RESETB controlled by host

Figure 41 shows the RESETB without host control.

VDD

RESETB

SX8648

RESETB_IN

Figure 41 Simplified diagr am of RESETB without host control

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4.4 Power management pins

The power management pins consist of the Power, Ground and Regulator pins.

VDD

VDD is a power pin and is the main power supply for the SX8648.

VDD has protection to GROUND.

Figure 42 shows a simplified diagram of the VDD pin.

VDD

SX8648

VDD

Figure 42 Simplified diagram of VDD

GND

The SX 8648 has four grou nd pins al l nam ed GND. T hese pins and th e pack age center pad ne ed to be c onnected

to ground potential.

The GND has protection to VDD.

Figure 43 shows a simplified diagram of the GND pin.

VDD

SX8648

GND GND

Figure 43 Simplified diagram of GND

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VANA, VDIG

The SX8648 has on-chip regulators for internal use (pins VANA and VDIG).

VANA and VDIG have protection to VDD and to GND.

The output of the regulators needs to be de-coupled with a small 100nF capacitor to ground.

Figure 44 shows a simplified diagram of the VANA and VDIG pin.

VDD

SX8648

GND

VDIG

VDD

GND

VANA

VDIG

Cvdig

Cvana

Figure 44 Simplified diagram of VANA and VDIG

4.5 General purpose IO pins

The SX8648 has 8 General purpose input/output (GPIO) pins.

All the GPIO pins have protection to VDD and GND.

The GPIO pins can be configured as GPI, GPO or GPP.

Figure 45 shows a simplified diagram of the GPIO pins.

Figure 45 Simplified diagram of GPIO pins

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5 DETAILED CONFIGURATION DESCRIPTIONS

5.1 Introduction

The SX 8648 configur ati on parameter s ar e taken from the QSM or the N VM and l oade d i nto th e SPM as ex p l ain ed

in the chapter ‘functional description’.

This chapter describes the details of the configuration parameters of the SX8648.

The SPM is split by functionality into 6 configuration sections:

• General section: operating modes,

• Capacitive Sensors section: related to lower level capacitive sensing,

• Button: related to the conversion from sensor data towards button information,

• Slider: related to the conversion from sensor data towards slider information,

• Mapping: related to mapping of button and slider information towards wake-up and GPIO pins,

• GPIO: related to the setup of the GPIO pins.

The total address space of the SPM and the NVM is 128 bytes, from address 0x00 to address 0x7F.

Two types of memory addresses, data are accessible to the user.

• ‘application data’: Application dependent data that need to be configured by the user.

• ‘reserved’: Data that need to be maintained by the user to the QSM default values (i.e. when NVM is burned).

The Table 12 and Table 13 resume the complete SPM address space and show the ‘application data’ and

‘reserved’ addresses, the functional split and the default values (loaded from the QSM).

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Address Name default QSM

value Address Name default QSM

value

0x00 Reserved 0xxx 0x20 Reserved 0x00

0x01 Reserved 0xxx 0x21 BtnCfg 0x30

0x02 Reserved 0x30 0x22 BtnAvgThresh 0x50

0x03 Reserved 0xxx 0x23 BtnCompNegThresh 0x50

0x04 I2CAddress 0x2B 0x24 BtnCompNegCntMax 0x01

0x05 ActiveScanPeriod 0x02 0x25 BtnHysteresis 0x0A

0x06 DozeScanPeriod 0x0D 0x26

Button

BtnStuckAtTimeout 0x00

0x07

General

PassiveTimer 0x00 0x27 SldCfg 0x00

0x08 Reserved 0x00 0x28 SldStuckAtTimeout 0x00

0x09 CapModeMisc 0x01 0x29 SldHysteresis 0x03

0x0A Reserved 0x00 0x2A Reserved 0xFF

0x0B CapMode7_4 0xAA 0x2B SldNormMsb 0x01

0x0C CapMode3_0 0xA5 0x2C SldNormLsb 0x80

0x0D CapSensitivity0_1 0x00 0x2D SldAvgThresh 0x50

0x0E CapSensitivity2_3 0x00 0x2E SldCompNegThresh 0x50

0x0F CapSensitivity4_5 0x00 0x2F SldCompNegCntMax 0x01

0x10 CapSensitivity6_7 0x00 0x30 SldMoveThresh 0x02

0x11 Reserved 0x00 0x31 Reserved 0x00

0x12 Reserved 0x00 0x32

Slider

Reserved 0x00

0x13 CapThresh0 0xA0 0x33 MapWakeupSize 0x00

0x14 CapThresh1 0xA0 0x34 MapWakeupValue0 0x00

0x15 CapThresh2 0xA0 0x35 MapWakeupValue1 0x00

0x16 CapThresh3 0xA0 0x36 MapWakeupValue2 0x00

0x17 CapThresh4 0xA0 0x37 MapAutoLight0 0xCC

0x18 CapThresh5 0xA0 0x38 MapAutoLight1 0xCC

0x19 CapThresh6 0xA0 0x39 MapAutoLight2 0xCC

0x1A CapThresh7 0xA0 0x3A MapAutoLight3 0x10

0x1B Reserved 0xA0 0x3B MapAutoLightGrp0Msb 0x40

0x1C Reserved 0xA0 0x3C MapAutoLightGrp0Lsb 0x00

0x1D Reserved 0xA0 0x3D MapAutoLightGrp1Msb 0x00

0x1E Reserved 0xA0 0x3E MapAutoLightGrp1Lsb 0x00

0x1F

Capacitive Sensors

CapPerComp 0x00 0x3F

Mapping

MapSegmentHysteresis 0x02

Table 12 SPM address map: 0x00…0x3F

Note

• ‘0xxx’: write p rotected data

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Address Name default QSM

value Address Name default QSM

value

0x40 GpioMode7_4 0x00 0x60 GpioDecTime1_0 0x44

0x41 GpioMode3_0 0x00 0x61 GpioOffDelay7_6 0x00

0x42 GpioOutPwrUp 0x00 0x62 GpioOffDelay5_4 0x00

0x43 GpioAutoLight 0xFF 0x63 GpioOffDelay3_2 0x00

0x44 GpioPolarity 0x00 0x64 GpioOffDelay1_0 0x00

0x45 GpioIntensityOn0 0xFF 0x65 GpioPullUpDown7_4 0x00

0x46 GpioIntensityOn1 0xFF 0x66 GpioPullUpDown3_0 0x00

0x47 GpioIntensityOn2 0xFF 0x67 GpioInterrupt7_4 0x00

0x48 GpioIntensityOn3 0xFF 0x68 GpioInterrupt3_0 0x00

0x49 GpioIntensityOn4 0xFF 0x69

Gpio

GpioDebounce 0x00

0x4A GpioIntensityOn5 0xFF 0x6A

Reserved 0x00

0x4B GpioIntensityOn6 0xFF 0x6B Reserved 0x00

0x4C GpioIntensityOn7 0xFF 0x6C Reserved 0x00

0x4D GpioIntensityOff0 0x00 0x6D Reserved 0x00

0x4E GpioIntensityOff1 0x00 0x6E Reserved 0x00

0x4F GpioIntensityOff2 0x00 0x6F Reserved 0x50

0x50 GpioIntensityOff3 0x00 0x70 Reserved 0x46

0x51 GpioIntensityOff4 0x00 0x71

Reserved 0x10

0x52 GpioIntensityOff5 0x00 0x72 Reserved 0x45

0x53 GpioIntensityOff6 0x00 0x73 Reserved 0x02

0x54 GpioIntensityOff7 0x00 0x74 Reserved 0xFF

0x55 Reserved 0xFF 0x75 Reserved 0xFF

0x56 GpioFunction 0x00 0x76 Reserved 0xFF

0x57 GpioIncFactor 0x00 0x77 Reserved 0xD5

0x58 GpioDecFactor 0x00 0x78 Reserved 0x55

0x59 GpioIncTime7_6 0x00 0x79 Reserved 0x55

0x5A GpioIncTime5_4 0x00 0x7A Reserved 0x7F

0x5B GpioIncTime3_2 0x00 0x7B Reserved 0x23

0x5C GpioIncTime1_0 0x00 0x7C Reserved 0x22

0x5D GpioDecTime7_6 0x44 0x7D Reserved 0x41

0x5E GpioDecTime5_4 0x44 0x7E Reserved 0xFF

0x5F

Gpio

GpioDecTime3_2 0x44 0x7F

SpmCrc* 0xA3

Table 13 SPM address map: 0x40…0x7F

Note*

• SpmCrc: CRC depending on SPM content, updated in Active or Doze mode.

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5.2 General Parameters

General Parameters

Address Name Bits Description

7 Reserved 0x04 I2CAddress

6:0 Defines the I2C address (default 0x2B).

The I2C address will be active after a reset.

0x05 ActiveScanPeriod 7:0 Active Mode Scan Period (Figure 7)

0x00: Reserved

0x01: 15ms

0x02: 30ms (default)

…

0xFF: 255 x 15ms

0x06 DozeScanPeriod 7:0 Doze Mode Scan Period (Figure 7)

0x00: Reserved

0x01: 15ms

…

0x0D: 195ms (default)

…

0xFF: 255 x 15ms

0x07 PassiveTimer 7:0 Passive Timer on Button and Slider Information (Figure 8)

0x00: OFF (default)

0x01: 1 second

…

0xFF: 255 seconds

Table 14 G ener al Par a m eter s

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5.3 Capacitive Sensors Parameters

Capacitive Sensors Parameters

Address Name Bits Description

7:3 Reserved

2 IndividualSensitivity Defines common sensitivity for all sensors or individual

sensor sensitiv ity .

0: Common settings (CapSensitivity0_1[7:4])

1: Individual CAP sensitivity settings (CapSensitivityx_x)

0x09 CapModeMisc

1:0 Reserved Reserved: ‘01’

0x0A Reserved 7:0 Reserved

7:6 CAP7 Mode Slider

5:4 CAP6 Mode Slider

3:2 CAP5 Mode Slider

0x0B CapMode7_4

1:0 CAP4 Mode Slider

7:6 CAP3 Mode Slider

5:4 CAP2 Mode Slider

3:2 CAP1 Mode Button

0x0C CapMode3_0

1:0 CAP0 Mode

Defines the mode of

the CAP pin.

00: Disabled

01: Button

10: Slider

11: Reserved

Default

Button

7:4 CAP0 Sensitivity - Common Sensitivity 0x0D CapSensitivity0_1

3:0 CAP1 Sensitivity

7:4 CAP2 Sensitivity 0x0E CapSensitivity2_3

3:0 CAP3 Sensitivity

7:4 CAP4 Sensitivity 0x0F CapSensitivity4_5

3:0 CAP5 Sensitivity

7:4 CAP6 Sensitivity 0x10 CapSensitivity6_7

3:0 CAP7 Sensitivity

Defines the sensitivity.

0x0: Minimum (default)

0x7: Maximum

0x8…0xF: Reserved

0x11 Reserved 7:0 Reserved

0x12 Reserved 7:0 Reserved

0x13 CapThresh0 7:0 CAP0 Touch Threshold

0x14 CapThresh1 7:0 CAP1 Touch Threshold

0x15 CapThresh2 7:0 CAP2 Touch Threshold

0x16 CapThresh3 7:0 CAP3 Touch Threshold

0x17 CapThresh4 7:0 CAP4 Touch Threshold

0x18 CapThresh5 7:0 CAP5 Touch Threshold

0x19 CapThresh6 7:0 CAP6 Touch Threshold

0x1A CapThresh7 7:0 CAP7 Touch Threshold

Defines the Touch Threshold ticks.

0x00: 0,

0x01: 4,

…

0xA0: 640 (default),

…

0xFF: 1020

0x1B Reserved 7:0 Reserved

0x1C Reserved 7:0 Reserved

0x1D Reserved 7:0 Reserved

0x1E Reserved 7:0 Reserved

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Capacitive Sensors Parameters

Address Name Bits Description

7:4 Reserved 0x1F CapPerComp

3:0 Periodic Offset Compensation Defines the periodic offset compensation.

0x0: OFF (default)

0x1: 1 second

0x2: 2 seconds

…

0x7: 7 seconds

0x8: 16 seconds

0x9: 18 seconds

…

0xE: 28 seconds

0xF: 60 seconds

Table 15 Capacitive Sensors Parameters

CapModeMisc

By default th e A SI is using a c om m on s ens itiv ity for all c apac iti ve sens or s as in t h e us ual c as e o verl a y m ateri al

and sensors sizes are about equal. The register bits CapSensitivity0_1[7:4] determine the sensitivity for all

sensors in common sensitivity mode.

In specia l appl ications it m ight be re quired to h ave a d iff erent, indi vidual, s ens itivit y for each C AP pin. T his c an

be obtained by setting bit CapModeMisc[2]. The individual sensitivity mode results in longer sensing periods

than required in common sensitivity mode.

CapMode7_4, CapMode3_0:

The CAP pins can be set as a button, part of a slider or disabled depending on the application.

minimum default maximum

buttons zero two four

slider one

(of four sensors) one

(of six sensors) one

(of eight sensors)

Table 16 Possible CAP pin modes

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Buttons and disabled CAP pins can be attributed freely (examples in Figure 46).

Figure 46 Button examples

Disabled CAP pins inside the slider sensor attribution sequence are allowed, but CAP buttons inside a slider

are not allowed (see example Figure 47 with CAP3 in a correct and a not allowed configuration).

Figure 47 Button and Slider good/bad configuration examples (I)

The physical order of the slider sensors on the PCB should correspond to the incremental CAP pin numbers.

Crossing slider PCB sensors and CAP number is not allowed. Figure 48 shows a valid configuration and a

wrong configuration where CAP5 andCAP6 are not routed correctly on the PCB.

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Figure 48 Button and Slider good/bad configuration examples (II)

The minimum position of the slider is associated to t he CAP pin, attributed to the slid er, with the lowest index

(in Figure 48 this is CAP2).

The m aximum position of the sli der is ass ocia ted to th e CAP pi n, attrib uted to th e s lider, with the highest i ndex

(in Figure 48 this is CAP6).

CapSensitivity0_1, CapSensitivity2_3, CapSensitivity4_5, CapSensitivity6_7:

The s ensitiv ity of the s ensor s can be s et bet wee n 8 va l ues. The higher th e s ens it iv it y is set the lar g er the val u e

of the ticks will be.

The minimum sensitivity can be used for thin overlay materials and large sensors, while the maximum

sensitivity is required for thicker overlay and smaller sensors.

The required sensitivity needs to be determined during a product development phase. Too low sensitivity

settings result in missing touches. Too high sensitivity settings will result in fault detection of fingers hovering

above the sensors.

The s ensitivit y is ident ical f or all sens ors in com m on sensit ivity m ode using the bi ts CapS ensit ivit y0_1[7:4] a nd

can be set individually using register CapModeMisc[2].

The m aximum num ber of ticks that can be obtain ed depends on the selecte d sensiti vity as illustr ated in T able

17.

Sensitivity Approximate

Maximum Tick Level

0 1000

1 2000

2 3000

3 4000

4 5000

5 6000

6 7000

7 8000

Table 17 ASI Maximum Tick Levels

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CapThresh0, CapThresh1, CapThresh2, CapThresh3, CapThresh4, CapThresh5, CapThresh6, CapThresh7:

For each CAP pin a threshold level can be set individually.

The threshold levels are used by the SX8648 for making touch and release decisions on e.g. touch or no-

touch.

The details are explained in the sections for buttons and slider.

CapPerComp:

The SX8648 offers a periodic offset compensation for applications which are subject to substantial

environmental changes. The periodic offset compensation is done at a defined interval and only if slider and

buttons are released.

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5.4 Button Parameters

Button Parameters

Address Name Bits Description

7:6 Defines the buttons events reporting method.

00: Multiple reporting of all touches and releases (default)

01: Single reporting of the first button touch. Next button touches and releases are

ignored until release of the first button.

10: Reserved

11: Reserved

5:4 Defines the buttons interrupt (for all buttons)

00 : Interrupts masked

01 : Triggered on Touch

10 : Triggered on Release

11 : Triggered on Touch and Release (default)

3:2 Defines the number of samples at the scan period for determining a release

00: OFF, use incoming sa mpl e (default)

01: 2 samples debounce

10: 3 samples debounce

11: 4 samples debounce

0x21 BtnCfg

1:0 Defines the number of samples at the scan period for determining a touch

00: OFF, use incoming sa mpl e (default)

01: 2 samples debounce

10: 3 samples debounce

11: 4 samples debounce

0x22 BtnAvgThresh 7:0 Defines the positive threshold for disabling the processing filter averaging.

If ticks are above the threshold, then the averaging is suspended

0x00: 0

0x01: 4

…

0x50: 320 (default)

…

0xFF: 1020

0x23 BtnCompNegThresh 7:0 Defines the negative offset co mpen sation threshold.

0x00: 0

0x01: 4

…

0x50: 320 (default)

…

0xFF: 1020

0x24 BtnCompNegCntMax 7:0 Defines the number of ticks (below the negative offset compensation threshold)

which will initiate an offset compensation.

0x00: Reserved

0x01: 1 sample (default)

…

0xFF-> samples

0x25 BtnHysteresis 7:0 Defines the button hysteresis corresponding to a percentage of the CAP thresholds

(defined in Table 18).

0x00: 0%

…

0x0A: 10% (default)

…

0x64: 100%

All buttons use the same hysteresis

0x26 BtnStuckAtTimeout 7:0 Defines the stuck at timeout.

0x00: OFF (default)

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Button Parameters

Address Name Bits Description

0x01: 1 second

…

0xFF: 255 seconds

Table 18 Button Conf iguration Paramet ers

A reliable button operation requires a coherent setting of the registers.

Figure 49 shows an example of a touch and a release. The ticks will vary slightly around the zero idle state.

When the touch occurs the ticks will rise sharply. At the release of the button the ticks will go down rapidly and

converge to the idle zero value.

ticks_diff

Figure 49 Touch and Release Example

As soon as the ticks become larger than the CAP thresholds (see registers of the previous section) plus the

hysteresis (defined in register BtnHysteresis) the debounce counter starts.

In the example of Figure 49 the touch is validated after 2 samples (BtnCfg [1:0] = 01).

The releas e is d etecte d im m ediatel y (BtnCfg [3:2] = 00) at the firs t sam ple which is bel ow the thr esh old m inus the

hysteresis.

BtnCfg

The SX 8648 can r e por t a ll t ouc hes of m ultiple finger s o r the SX 86 48 c an be set to r epor t on ly the f ir st det ec te d

touch. In the later case all succeeding touches are ignored. The very first touch should be released before a

next touch will be detected.

The user can select to have the interrupt signal on touching a button, releasing a button or both

In noisy environments it may be required to debounce the touch and release detection decision.

In case the debounce is enabled the SX8648 will count up to the number of debounce samples BtnCfg [1:0],

BtnCfg [3:2] before taking a touch or release decision. The sample period is identical to the scan period.

BtnAvgThresh

Small environmental and system noise cause the ticks to vary slowly around the zero idle mode value.

In case the ticks get slightly positive this is considered as normal operation. Very large positive tick values

indicate a valid touch. The averaging filter is disabled as soon as the average reaches the value defined by

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BtnAvgThresh. This mechanism avoids that a valid touch will be averaged and finally the tick difference

becomes zero.

In case three or more sensors reach the BtnAvgThresh value simultaneously then the SX8648 will start an

offset compensation procedure.

Small environmental and system noise cause the ticks to vary slowly around the zero idle mode value.

In case the ticks get slightly negative this is considered as normal operation. However large negative values will

trigger an offset compensation phase and a new set of DCVs will be obtained.

The decision to trigger a compensation phase based on negative ticks is determined by the value in the register

BtnCompNegThresh and by the number of ticks below the negative thresholds defined in register

BtnCompNegCntMax. An example is shown in Figure 50.

ticks_diff

Figure 50 Negative Ticks Offset Compensation Trigger

BtnCompNegThresh

Small negative ticks are considered as normal operation and will occur very often.

Larger negative ticks however need to be avoided and a convenient method is to trigger an offset

compensation phase. The new set of DCV will assure the idle ticks will be close to zero again.

A trade-off has to be found for the value of this register. A negative threshold too close to zero will trigger a

compensation phase very often. A very negative threshold will never trigger.

BtnCompNegCntMax

As soon as the ticks get smaller than the Negative Threshold the Negative Counter starts to count.

If the counter goes beyond the Negative Counter Max then the offset compensation phase is triggered.

The re comm ended va lue f or this r egister is ‘1 ’ which m eans that th e off set c ompens ation s tarts on the fir st tick

below the negative threshold.

BtnHysteresis

The hysteresis percentage is identical for all buttons.

A touch is detected if the ticks are getting larger as the value defined by:

CapThreshold + CapThreshold * hysteresis.

A release is detected if the ticks are getting smaller as the value defined by:

CapThreshold - CapThreshold * hysteresis.

BtnStuckAtTimeout

The stuckat timer can avoid sticky buttons.

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If the stuc kat timer is set to one sec ond then th e touch of a f inger will las t only for one second an d consid ered

released, even if the finger remains on the button for a longer time. After the actual finger release the button

can be touched again and will be reported as usual.

In case the stuckat timer is not required it can be set to zero.

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5.5 Slider Parameters

Slider Parameters

Address Name Bits Description

7:4 Reserved

3:2 Defines the number of samples at the scan period for determining a release

00: OFF, use incoming sa mpl e (default)

01: 2 samples debounce

10: 3 samples debounce

11: 4 samples debounce

0x27 SldCfg

1:0 Defines the number of samples at the scan period for determining a touch

00: OFF, use incoming sa mpl e (default)

01: 2 samples debounce

10: 3 samples debounce

11: 4 samples debounce

0x28 SldStuckAtTimeout 7:0 Defines the stuck at timeout.

0x00: OFF (default)

0x01: 1 second

…

0xFF: 255 seconds

0x29 SldHysteresis 7:0 Defines the Slider Touch/Release Hysteresis.

0x00: 0

0x01: 4

…

0x03: 12 (default)

…

0xFF: 1020

0x2B SldNormMsb 7:0 Slider Norm Msb

0x2C SldNormLsb 7:0 Slider Norm Lsb

Defines the 16 bits slider norm (default 0x0180)

0x2D SldAvgThresh 7:0 Defines the positive threshold for disabling the processing filter averaging.

If ticks are above the threshold, then the averaging is suspended

0x00: 0

0x01: 4

…

0x50: 320 (default)

…

0xFF: 1020

0x2E SldCompNegT hresh 7:0 Defines the negative offs et co mpen sat ion thre shold.

0x00: 0

0x01: 4

…

0x50: 320 (default)

…

0xFF: 1020

0x2F SldCompNegCntMax 7:0 Defines the number of ticks (below the negative offset compensation threshold)

which will initiate an offset compensation.

0x00: Reserved

0x01: 1 sample (default)

…

0xFF: 255 samples

0x30 SldMoveThresh 7:0 Defines the threshold for detecting a move high or move low.

The threshold is a percentage of the maximum slider position.

0x00: 0%

…

0x02: 2% (default)

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Slider Parameters

Address Name Bits Description

…

0x64: 100%

A succeeding position difference, at the scan period, above the threshold is

considered as a move high or move low.

Table 19 Slider Parameters

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The pressure represents the finger touch on the sensors of the slider and it used to determine if a slider is

touched or released.

∑

−

−=

0))()(_(

iiCapThreshidifftickseSldPressur

- N is the number of sensors,

- A sensor with ticks smaller than the CapThreshold is not taken into account for calculating the pressure

In case the pressure equals zero the slider status is released.

In case the pressure is larger as the Slider Hysteresis the slider status is touched.

The position of a finger on a slider is calculated by the centre of gravity algorithm.

∑

−

∗= 1

))()(_(

))()(_(*

32 N

iCapThreshidiffticks

iCapThreshidiffticksi

SldNorm

SldPos

- N is the number of sensors,

- A sensor with ticks smaller than the CapThreshold is not taken into account for calculating the position,

- SldNorm[15:0] is a 16 bit number determined by SldNormMsb[15:8] and SldNormLsb[7:0].

- SldPos is the slider position (16 bits) which can be read by the host over the I2C registers SldPosMsb and

SldPosLsb

Figure 51 Slider Position

Figure 51 shows an example of a slider composed of 6 sensors (CAP0, CAP1… CAP5).

The default slider norm value 12 (SldNormMsb = 0x01, SldNormLsb = 0x80), is taken for the example.

A touch on CAP0 gives the slider position: 0.

A touch on CAP1 gives the slider position: 12.

A touch on CAP5 gives the slider position: 60.

If a touch occurs on CAP0 and CAP1 the centre of gravity algorithm will interpolate.

Assuming the touch is identically distributed on CAP0 and CAP1 then the position will be: 6

Assuming the touch is identically distributed on CAP1 and CAP2 then the position will be: 18

Assuming the touch is identically distributed on CAP4 and CAP5 then the position will be: 54

The maximum slider position (for this example) that can be obtained is 60.

The minimum position of a slider equals 0.

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The maximum position (SldPosMax) is defined by:

()

32 −×= N

SldNorm

SldPosMax

with:

N is the number of sensors in the slider

Slow varying slider ticks due to environmental changes are handled as buttons in the previous section.

If the ticks pass below the slider negative threshold for more than the compensation negative max counter then an

offset compensation phase will be triggered.

If the ticks pass above the slider average positive threshold then the averaging filters will be held.

A finger that m oves ver y slo wly over the slider is not c onsider ed as a movem ent. T he status m ove low and m ove

high will not be set.

A finger that moves faster on the slider will change the movement status.

A movement is detected if the difference of the position for two succeeding samples at the scanning rate goes

beyond the movement threshold (SldMoveThresh). A large movement threshold requires very rapid finger

movements, while a small movement threshold detects more easily movements but gets sensitive to noise

variations as well.

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5.6 Mapping Parameters

Mapping Parameters

Address Name Bits Description

7:3 Reserved 0x33 MapWakeupSize

2:0 Doze -> Active wake up sequence size.

0: Any sensor event (default)

1: key0

2: key0, key1

…

6: key0, key1,…key5

7: No sensor event, only GPI or I2C cmd can exit Doze mode

Each key must be followed by a release to be validated.

Any other sensor event before the release is ignored.

Any wrong key implies the whole sequence to be entered again.

7:4 key5 0x34 MapWakeupValue0

3:0 key4

7:4 key3 0x35 MapWakeupValue1

3:0 key2

7:4 key1 0x36 MapWakeupValue2

3:0 key0

Defines the sensor event associated to each key.

0x00: Btn0 (default)

0x01: Btn1

…

0x07: Btn7

0x08…0xA : Reserved

0x0C: Slider Touch

0x0D: Move Low

0x0E: Move High

0x0F: Reserved

7:4 GPIO[7] 0x37 MapAutoLight0

3:0 GPIO[6]

7:4 GPIO[5] 0x38 MapAutoLight1

3:0 GPIO[4]

7:4 GPIO[3] 0x39 MapAutoLight2

3:0 GPIO[2]

7:4 GPIO[1] 0x3A MapAutoLight3

3:0 GPIO[0]

Defines the mapping between GPOs (with

Autolight ON) and sensor events.

0x00: Btn0 (default)

0x01: Btn1

…

0x07: Btn7

0x08…0x0B : Reserved

0x0C: Group0 as defined by MapAutoLightGrp0

0x0D: Group1 as defined by MapAutoLightGrp1

0x0E: Move Low

0x0F: Move High

Several GPOs can be mapped to the same sensor

event and will be controlled simultaneously.

7 Reserved

6 Segment

5 Move High

4 Move Low

0x3B MapAutoLightGrp0Msb

3:0 Reserved

7 Btn7

6 Btn6

5 Btn5

4 Btn4

3 Btn3

2 Btn2

0x3C MapAutoLightGrp0Lsb

1 Btn1

Defines Group0 sensor events:

0: OFF (default)

1: ON

If any of the enabled sensor events occurs the

Group0 event will occur as well.

All sensors events within the group can be

independently set except slider event Segment

which is exclusive (ie must be the only one

enabled to be used)

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Mapping Parameters

Address Name Bits Description

0 Btn0

7 Reserved

6 Slider Touch

5 Move High

4 Move Low

0x3D MapAutoLightGrp1Msb

3:0 Reserved

7 Btn7

6 Btn6

5 Btn5

4 Btn4

3 Btn3

2 Btn2

1 Btn1

0x3E MapAutoLightGrp1Lsb

0 Btn0

Defines Group1 sensor events:

0: OFF (default)

1: ON

If any of the enabled sensor events occurs the

Group0 event will occur as well.

All sensors events within the group can be

independently set.

0x3F MapSegmentHysteresis 7:0 Defines the position hysteresis for detecting a segment change.

The hysteresis is defined as a percentage of the maximum slider position.

0x00: 0%

…

0x02: 2% (default)

…

0x64: 100%

This hysteresis applies to all segments of the slider.

Table 20 Mapping Parameters

MapWakeupSize

The number of keys defining the wakeup sequence can be set from 1 to 6.

If the size is set to 0 then wakeup is done on any sensor event.

if the size is set to 6 then wakeup is done only by GPI or an I2C command.

MapWakeupValue0, MapWakeupValue1, MapWakeupValue2

For the wakeup sequence Btn2 -> Btn5 -> Btn6 ->Btn0 the required register settings are:

- MapWakeupSize set to 0x04,

- key0 = 0x2

- key1 = 0x5

=> MapWakeupValue2 set to 0x52

- key2 = 0x6

- key3 = 0x0

=> MapWakeupValue2 set to 0x06

MapAutoLight0, MapAutoLight1, MapAutoLight2, MapAutoLight3

MapAutoLi ghtG rp0 Ms b, Ma pAut oL ightG r p 0Lsb, Map A utoL igh t Gr p1Msb, MapAuto Lig htG r p1Lsb

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Thes e regis ter s d efine the mapping b et ween the G PO pi ns ( with Autolight ON) and the s e ns or inform ation wh ich

will control its ON/OFF state.

The mapping can be done to a specific sensor event but also on groups (in this case an y sensor event in the

group will contr ol the GPO ).

Table 21 defines for each selectable sensor event, which action will trigger corresponding GPO to switch ON

or OFF.

MapAutoLight GPO ON GPO OFF

BtnX Touch Release

Slider Touch Touch Release

Slider Move High Mo ve High Move Low or Release

Slider Move Low Move Low Move High or Release

Slider Segment Segment Touched Segment Released

Table 21 Autolight Mapping, Sensor Inform ation

Examples:

- If GPO[0] should change state accordingly to Btn4 then MapAutoLight3[3:0] should be set to 0x04.

- If GPO[0] should change state accordingly to Btn0 or Btn1 then Group0 can be used as following:

- MapAutoLight3[3:0] should be set to 0x0C (ie Group0).

- MapAutoLightGrp0 should be set to 0x0003 (ie Btn0 or Btn1)

W hen the Sli der S egment e ven t is mapped, t he n umber of G POs m apped to it de t er mines the number of slider

segments. The GPO with the lowest pin index is mapped on the segment with the smallest positions.

E.g. if two GPOs (e.g.GPO[0] and GPO[1]) are mapped to the Slider Segment event then the slider is split in

two segments . GPO [0] will turn O N f or a t ouc h on the s lider s egment [0, S ld PosM ax /2] a nd G PO[1 ] f or a touch

on the slider segment [SldPosMax/2, SldPosMax].

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5.7 GPIO Parameters

GPIO Parameters

Address Name Bits Description

7:6 GPIO[7] Mode

5:4 GPIO[6] Mode

3:2 GPIO[5] Mode

0x40 GpioMode7_4

1:0 GPIO[4] Mode

7:6 GPIO[3] Mode

5:4 GPIO[2] Mode

3:2 GPIO[1] Mode

0x41 GpioMode3_0

1:0 GPIO[0] Mode

Defines the GPIO mode.

00: GPO (default)

01: GPP

10: GPI

11: Reserved

GPIO[7] Output Value at Power Up

GPIO[6] Output Value at Power Up

GPIO[5] Output Value at Power Up

GPIO[4] Output Value at Power Up

GPIO[3] Output Value at Power Up

GPIO[2] Output Value at Power Up

GPIO[1] Output Value at Power Up

0x42 GpioOutPwrUp 7:0

GPIO[0] Output Value at Power Up

Defines the values of GPO and GPP pins

after power up ie default values of I2C

parameters GpoCtrl and GppIntensity

respectively.

0: OFF(GPO) / IntensityOff (GPP) (default)

1: ON (GPO) / IntensityOn (GPP)

Bits corresponding to GPO pins with

Autolight ON should be left to 0.

Before being actually initialized GPIOs are

set as inputs with pull up.

GPIO[7] AutoLight

GPIO[6] AutoLight

GPIO[5] AutoLight

GPIO[4] AutoLight

GPIO[3] AutoLight

GPIO[2] AutoLight

GPIO[1] AutoLight

0x43 GpioAutoLight 7:0

GPIO[0] AutoLight

Enables Autolight in GPO mode

0 : OFF

1 : ON (default)

GPIO[7] Output Polarity

GPIO[6] Output Polarity

GPIO[5] Output Polarity

GPIO[4] Output Polarity

GPIO[3] Output Polarity

GPIO[2] Output Polarity

GPIO[1] Output Polarity

0x44 GpioPolarity 7:0

GPIO[0] Output Polarity

Defines the polarity of the GPO and GPP

pins.

0: Inverted (default)

1: Normal

0x45 GpioIntensityOn0

0x46 GpioIntensityOn1

0x47 GpioIntensityOn2

7:0 ON Intensity Index

Defines the ON intensity index

0x00: 0

0x01: 1

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GPIO Parameters

Address Name Bits Description

0x48 GpioIntensityOn3

0x49 GpioIntensityOn4

0x4A GpioIntensityOn5

0x4B GpioIntensityOn6

0x4C GpioIntensityOn7

…

0xFF: 255 (default)

0x4D GpioIntensityOff0

0x4E GpioIntensityOff1

0x4F GpioIntensityOff2

0x50 GpioIntensityOff3

0x51 GpioIntensityOff4

0x52 GpioIntensityOff5

0x53 GpioIntensityOff6

0x54 GpioIntensityOff7

7:0 OFF Intensity Index

Defines the OFF intensity index

0x00: 0 (default)

0x01: 1

…

0xFF: 255

GPIO[7] Function

GPIO[6] Function

GPIO[5] Function

GPIO[4] Function

GPIO[3] Function

GPIO[2] Function

GPIO[1] Function

0x56 GpioFunction 7:0

GPIO[0] Function

Defines the intensity index vs PWM pulse

width function.

0: Logarithmic (default)

1: Linear

GPIO[7] Fading Increment Factor

GPIO[6] Fading Increment Factor

GPIO[5] Fading Increment Factor

GPIO[4] Fading Increment Factor

GPIO[3] Fading Increment Factor

GPIO[2] Fading Increment Factor

GPIO[1] Fading Increment Factor

0x57 GpioIncFactor 7:0

GPIO[0] Fading Increment Factor

Defines the fading increment factor.

0: 1, intensity index incremented every

increment time (default)

1: 16, intensity index incremented every 16

increment times

GPIO[7] Fading Decrement Factor

GPIO[6] Fading Decrement Factor

GPIO[5] Fading Decrement Factor

GPIO[4] Fading Decrement Factor

GPIO[3] Fading Decrement Factor

GPIO[2] Fading Decrement Factor

GPIO[1] Fading Decrement Factor

0x58 GpioDecFactor 7:0

GPIO[0] Fading Decrement Factor

Defines the fading decrement factor.

0: 1, intensity index decremented every

decrement time (default)

1: 16, intensity index decremented every 16

decrement times

0x59 GpioIncTime7_6 7:4 GPIO[7] Fading Increment Time Defines the fading increment time.

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GPIO Parameters

Address Name Bits Description

3:0 GPIO[6] Fading Increment Time

7:4 GPIO[5] Fading Increment Time 0x5A GpioIncTime5_4

3:0 GPIO[4] Fading Increment Time

7:4 GPIO[3] Fading Increment Time 0x5B GpioIncTime3_2

3:0 GPIO[2] Fading Increment Time

7:4 GPIO[1] Fading Increment Time 0x5C GpioIncTime1_0

3:0 GPIO[0] Fading Increment Time

0x0: OFF (default)

0x1: 0.5ms

0x2: 1ms

…

0xF: 7.5ms

The total fading in time will be:

GpioIncTime*GpioIncFactor*

(GpioIntensityOn – GpioIntensityOff)

7:4 GPIO[7] Fading Decrement Time 0x5D GpioDecTime7_6

3:0 GPIO[6] Fading Decrement Time

7:4 GPIO[5] Fading Decrement Time 0x5E GpioDecTime5_4

3:0 GPIO[4] Fading Decrement Time

7:4 GPIO[3] Fading Decrement Time 0x5F GpioDecTime3_2

3:0 GPIO[2] Fading Decrement Time

7:4 GPIO[1] Fading Decrement Time 0x60

GpioDecTime1_0

3:0 GPIO[0] Fading Decrement Time

Defines the fading decrement time.

0x0: OFF

0x1: 0.5ms

0x2: 1ms

…

0x4: 2.0ms (default)

…

0xF: 7.5ms

The total fading out time will be:

GpioDecTime*GpioDecFactor*

(GpioIntensityOn – GpioIntensityOff)

7:4 GPIO[7] OFF Delay 0x61 GpioOffDelay7_6

3:0 GPIO[6] OFF Delay

7:4 GPIO[5] OFF Delay 0x62 GpioOffDelay5_4

3:0 GPIO[4] OFF Delay

7:4 GPIO[3] OFF Delay 0x63 GpioOffDelay3_2

3:0 GPIO[2] OFF Delay

7:4 GPIO[1] OFF Delay 0x64 GpioOffDelay1_0

3:0 GPIO[0] OFF Delay

Defines the delay after GPO OFF trigger

before fading out starts.

0x0: OFF (default)

0x1: 200ms

0x2: 400ms

…

0xF: 3000ms

7:6 GPIO[7] Pullup/down

5:4 GPIO[6] Pullup/down

3:2 GPIO[5] Pullup/down

0x65 GpioPullUpDown7_4

1:0 GPIO[4] Pullup/down

7:6 GPIO[3] Pullup/down

5:4 GPIO[2] Pullup/down

3:2 GPIO[1] Pullup/down

0x66 GpioPullUpDown3_0

1:0 GPIO[0] Pullup/down

Enables pullup/down resistors for GPI pins.

00 : None (default)

01 : Pullup

10 : Pulldown

11 : Reserved

7:6 GPI[7] Interrupt

5:4 GPI[6] Interrupt

3:2 GPI[5] Interrupt

0x67 GpioInterrupt7_4

1:0 GPI[4] Interrupt

7:6 GPI[3] Interrupt

5:4 GPI[2] Interrupt

0x68 GpioInterrupt3_0

3:2 GPI[1] Interrupt

Defines the GPI edge which will trigger INTB

falling edge and exit Sleep/Doze modes if

relevant.

00 : None (default)

01 : Rising

10 : Falling

11 : Both

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GPIO Parameters

Address Name Bits Description

1:0 GPI[0] Interrupt

GPI[7] Debounce

GPI[6] Debounce

GPI[5] Debounce

GPI[4] Debounce

GPI[3] Debounce

GPI[2] Debounce

GPI[1] Debounce

0x69 GpioDebounce 7:0

GPI[0] Debounce

Enables the GPI debounce (done on 10

consecutive samples at 1ms).

0 : OFF (default)

1 : ON

Table 22 GPIO Parameters

Table 23 resumes the applicable SPM and I2C parameters for each GPIO mode.

GPI GPP GPO

GpioMode X X X

GpioOutPwrUp X

1 X2

GpioAutoligth X

GpioPolarity X X

GpioIntensityOn X

1 X

GpioIntensityOff X

1 X

GpioFunction X X

GpioIncFactor X

GpioDecFactor X

GpioIncTime X

GpioDecTime X

GpioOffDelay X

GpioPullUpDown X

GpioInterrupt X

SPM

GpioDebounce X

IrqSrc[4] X

GpiStat X

GpoCtrl X

GppPinId X

I2C

GppIntensity X

1 At power up, GppIntensit y of each GPP pin is initialized with GpioIntens ityOn or Gpi oInt ensityOff depending on GpioOutPwrUp

corresponding bits val ue.

2 Only if Autolight is OFF, else must be left to 0 (default value)

3 Only if Autolight is OFF, else ignored

Table 23 Appl icable SPM/ I2C Parameters vs. GPIO Mode

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6 I2C INTERFACE

The I2C implemented on the SX8648 is compliant with:

- standard (100kb/s), fast mode (400kb/s)

- slave mode

- 7 bit address (default 0x2B). The default address can be changed in the NVM at address 0x04.

The host can use the I2C to read and write data at any time. The effective changes will be applied at the next

process ing phase (s ect ion 3.3).

Three types of registers are considered:

- status ( read). Thes e register s give inf ormation abo ut the stat us of the c apacitive buttons, sli der, GPIs, oper ation

modes etc…

- control (read/write). These registers control the soft reset, operating modes, GPIOs and offset compensation.

- SPM gateway (read/write). These registers are used for the communication between host and the SPM. The

SPM gateway communication is done typically at power up and is not supposed to be changed when the

application is running. The SPM needs to be re-stored each time the SX8648 is powered down.

The SPM c an be stored pe rmanentl y in the NVM m emory of the SX8648. T he SPM gate way comm unication over

the I2C at power up is then not required.

The I2C will be able to rea d and write from a start address and then perform read or writes sequentiall y, and the

address increments automatically.

The supported I2C access formats are described in the next sections.

6.1 I2C Write

The format of the I2C write is given in Figure 52.

After the start condition [S], the slave address (SA) is sent, followed by an eighth bit (‘0’) indicating a Write. The

SX8648 the n Acknowled ges [A] that it is bei ng addressed, and t he Master s ends an 8 bit Data Byte cons isting of

the SX864 8 Re gis ter Ad dr e ss ( RA) . T he Sla ve Ac k nowled ges [ A] a nd the m as ter s ends th e a ppr opriat e 8 bit Data

Byte (W D0). Again the Sla ve Acknowledg es [A]. In case the m aster needs to wr ite mor e data, a succeeding 8 bit

Data Byte will follow (WD1), acknowledged by the slave [A]. This sequence will be repeated until the master

terminates the transfer with the Stop condition [P].

Figure 52 I2C write

The regis ter addres s is inc rem ented autom atically whe n succ essive regis ter data (W D1...WD n) is supplied b y the

master.

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6.2 I2C read

The format of the I2C read is given in Figure 53.

After the start condition [S], the slave address (SA) is sent, followed by an eighth bit (‘0’) indicating a Write. The

SX8648 t hen Ack nowledge s [A] that it is being a ddress ed, and the Master responds with an 8 bit Da ta consis ting

of the Register Address (RA). The Slave Acknowledges [A] and the master sends the Repeated Start Condition

[Sr]. Once again, the slave address (SA) is sent, followed by an eighth bit (‘1’) indicating a Read.

The SX 8648 responds with an Ackno wle dge [A] and t he read Data b yte (RD 0). If the m aster needs to re ad more

data it will acknowledge [A] and the SX8648 will send the next read b yte (RD1). T his sequence can be repeated

until the master terminates with a NACK [N] followed by a stop [P].

Figure 53 I2C read

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6.3 I2C Registers Overview

Address Name R/W Description

0x00 IrqSrc read Interrupt Source

0x01 CapStatMsb read Slider/Button Status MSB

0x02 CapStatLsb read Button Status LSB

0x03 SldPosMsb read Slider Position MSB

0x04 SldPosLsb read Slider Position LSB

0x05 Reserved

0x06 Reserved

0x07 GpiStat read GPI Status

0x08 SpmStat read SPM Status

0x09 CompOpMode read/write

Compensation and

Operating Mode

0x0A GpoCtrl read/write GPO Control

0x0B GppId read/write GPP Pin Selection

0x0C GppIntensity read/write GPP Intensity

0x0D SpmCfg read/write SPM Configuration

0x0E SpmBaseAddr read/write SPM Base Address

0x0F Reserved

0xAC SpmKeyMsb read/write SPM Key MSB

0xAD SpmkeyLsb read/write SPM Key LSB

0xB1 SoftReset read/write Software Reset

Table 24 I 2C Regist ers Overview

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6.4 Status Registers

Address Name Bits Description

7 Reserved

6 NVM burn interrupt flag

5 SPM write interrupt flag

4 GPI interrupt flag

3 Slider interrupt flag

2 Buttons interrupt flag

1 Compensation interrupt flag

0x00 IrqSrc

0 Operating Mode interrupt flag

Interrupt source flags

0: Inactive (default)

1: Active

INTB goes low if any of

these bits is set.

More than one bit can be

set.

Reading IrqSrc clears it

together with INTB.

Table 25 I nt errupt Source

The delay between the actual event and the flags indicating the interrupt source may be one scan period.

IrqSrc[6] is set once NVM burn procedure is completed.

IrqSrc[5] is set once SPM write is effective.

IrqSrc[4] is set if a GPI edge as programmed in GpioInterrupt occurred. GpiStat shows the detailed status of the

GPI pins.

IrqSrc[3] is s et if a S lider e vent occ urred (touc h, r elea se, m ove h igh, m ove low o r posit ion c hange) . C apSta tMsb,

SldPosMsb and SldPosLsb show the detailed status of the Slider.

IrqSrc[2] is set if a Button event occurred (touch or release if enabled). CapStatMsb and CapStatLsb show the

detailed status of the Buttons.

IrqSrc[1] is set once compensation procedure is completed either through automatic trigger or via host request.

IrqSrc[0] is set when actual ly entering Activ e or Doze mode either through autom atic wakeup or vi a host request.

CompOpmode shows the current operation mode.

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Address Name Bits Description

7 Reserved

6 Slider Move High

5 Slider Move Low

Slider Move status

0: No move (default)

1: Move

The status remains high as long as the slider is

touched and no opposite move has occurred.

4 Slider Touched Slider Touch status

0: Released (default)

1: Touched

0x01 CapStatMsb

3:0 Reserved

7 Button 7 Touched

6 Button 6 Touched

5 Button 5 Touched

4 Button 4 Touched

3 Button 3 Touched

2 Button 2 Touched

1 Button 1 Touched

0x02 CapStatLsb

0 Button 0 Touched

Button Touch status

0: Released (default)

1: Touched

Table 26 Slider, Button status MSB/LSB

Address Name Bits Description

0x03 SldPosMsb 7:0 Slider Position[15:8]

0x04 SldPosLsb 7:0 Slider Position[7:0]

Shows the current (touched) or last (released)

slider position[15:0] unsigned (default 0x00)

Table 27 Slider position MSB/LSB

Address Name Bits Description

0x07 GpiStat 7:0 GPI[7:0]

Status

Status of each individual GPI pin

0: Low

1: High

Bits of non-GPI pins are set to 0.

Table 28 I2C GPI status

Address Name Bits Description

0x08 SpmStat

7:4 reserved

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Address Name Bits Description

3 NvmValid

Indicates if the current NVM is valid.

0: No – QSM is used

1: Yes – NVM is used

2:0 NvmCount

Indicates the number of times NVM has been burned:

0: None – QSM is used (default)

1: Once – NVM is used if NvmValid = 1, else QSM.

2: Twice – NVM is used if NvmValid = 1, else QSM.

3: Three times – NVM is used if NvmValid = 1, else QSM.

4: More than three times – QSM is used

Table 29 I 2C SPM status

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6.5 Control Registers

Address Name Bits Description

7:3 Reserved*, write only ‘00000’

2 Compensation

Indicates/triggers compensation procedure

0: Compensation completed (default)

1: read -> compensation running ; write -> trigger

compensation

0x09 CompOpMode

1:0 Operating Mode

Indicates/programs** operating mode

00: Active mode (default)

01: Doze mode

10: Sleep mode

11: Reserved

Table 30 I 2C com pensat ion, operation modes

* The reading of these reserved bits will return varying values.

** After the operating mode change (Active/Doze) the host should wait for INTB or 300ms before

performing any I2C read access.

Address Name Bits Description

0x0A GpoCtrl 7:0 GpoCtrl[7:0]

Triggers ON/OFF state of GPOs when Autolight is

OFF

0: OFF (ie go to IntensityOff)

1: ON (ie go to IntensityOn)

Default is set by SPM parameter GpioOutPwrUp

Bits of non-GPO pins are ignored.

Table 31 I2C GPO Control

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Address Name Bits Description

7:3 Reserved, write only ‘00000’

0x0B GppPinId 2:0 GPP Pin Identifier

Defines the GPP pin to which the GppIntensity is

assigned for the following read/write operations

0x0 = GPP0 (default)

0x1 = GPP1

...

0x7 = GPP7

GPPx refers to pin GPIOx configured as GPP

Table 32 I2C GPP Pin Identifier

Address Name Bits Description

0x0C GppIntensity 7:0

Defines the intensity index of the GPP pin selected in GppPinId

0x00: 0

0x01: 1

…

0xFF: 255

Reading returns the intensity index of the GPP pin selected in GppPinId.

Default value is IntensityOn or IntensityOff depending on GpioOutPwrUp.

Table 33 I2C GPP Intensity

Address Name Bits Description

0xB1 SoftReset 7:0 Writing 0xDE followed by 0x00 will reset the chip.

Table 34 I2C Soft Reset

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6.6 SPM Gateway Registers

The SX8648 I2C interface offers two registers for exchanging the SPM data with the host.

• SpmCfg

• SpmBaseAddr

Address Name Bits Description

7:6 00: Reserved

5:4

Enables I2C SPM mode

00: OFF (default)

01: ON

10: Reserved

11: Reserved

3 Defines r/w direction of SPM

0: SPM write access (default)

1: SPM read access

0x0D SpmCfg

2:0 000: Reserved

Table 35 SPM access configuration

Address Name Bits Description

0x0E SpmBaseAddr 7:0 SPM Base Address (modulo 8).

The lowest address is 0x00 (default).

The highest address is 0x78.

Table 36 SP M Base Ad dress

The exchange of data, read and write, between the host and the SPM is always done in bursts of eight bytes.

The base address of each burst of eight bytes is a modulo 8 number, starting at 0x00 and ending at 0x78.

The registers SpmKeyMsb and SpmKeyLsb are required for NVM programming as described in section 6.7.

Address Name Bits Description

0xAC SpmKeyMsb 7:0 SPM to NVM burn Key MSB Unlock requires writing data: 0x62

Table 37 SPM Key MSB

Address Name Bits Description

0xAD SpmKeyLsb 7:0 SPM to NVM burn Key LSB Unlock requires writing data: 0x9D

Table 38 SPM Key LSB

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6.6.1 SPM Write Sequence

The SPM write can be done in any mode (Active, Doze, Sleep). Writing the SPM in Sleep is useful to avoid

potential transient behaviors.

The SPM must always be written in blocks of 8 bytes. The sequence is described below:

1. Set the I2C in SPM mode by writing “01” to SpmCfg[5:4] and SPM write access by writing ‘0’ to SpmCfg[3].

2. Write the SPM base address to SpmBaseAddr (The base address needs to be a value modulo 8).

3. Write the eight consecutive bytes to I2C address 0, 1, 2, …7

4. Terminate by writing “000” to SpmCfg[5:3].

Figure 54: SP M Write Sequ enc e

The complete SPM can be written by repeating 16 times the cycles shown in Figure 54 using base addresses

0x00, 0x08, 0x10, …, 0x70, 0x78. Between each sequence the host should wait for INTB (Active/Doze) or 30ms

in Sleep.

In Active or Doze mode, once the SPM write sequence is actually applied, the INTB pin will be asserted and

IrqSrc[5] set. In Sleep mode the SPM write can be actually applied with a delay of 30ms.

The host clears the interrupt and IrqSrc[5] by reading the IrqSrc register.

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6.6.2 SPM Read Sequence

The SPM read can be done in any mode (Active, Doze, Sleep).

The SPM must always be read in blocks of 8 bytes. The sequence is described below:

1. Set the I2C in SPM mode by writing “01” to SpmCfg[5:4] and SPM read access by writing ‘1’ to SpmCfg[3].

2. Write the SPM base address to SpmBaseAddr (The base address needs to be a value modulo 8).

3. Read the eight consecutive bytes from I2C address 0, 1, 2, …7

4. Terminate by writing “000” to SpmCfg[5:3].

Figure 55: SP M Read Sequ enc e

The c omplete SPM c an be read b y repeati ng 16 tim es the cycles s hown in Fig ure 55 using bas e addr esses 0x00,

0x08, 0x10, …, 0x70, 0x78.

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6.7 NVM burn

The content of the SPM can be copied permanently (burned) into the NVM to be used as the new default

parameters. The burning of the NVM can be done up to three times and must be done only when the SPM is

completely written with the desired data. The NVM burn must be done in Active or Doze mode.

Once the NVM burn process is terminated IrqSrc[6] will be set and INTB asserted.

After a reset the burned NVM parameters will be copied into the SPM.

The number of times the NVM has been burned can be monitored by reading NvmCount from the I2C register

SpmStat[2:0].

Figure 56 Simplified Diagram NvmCount

Figure 56 shows the simplified diagram of the NVM counter. The SX8648 is delivered with empty NVM and

NvmCount set to zero. The SPM points to the QSM.

Each NVM burn will increase the NvmCount. At the fourth NVM burn the SX8648 switches definitely to the QSM.

The burning of the SPM into the NVM is done by executing a special sequence of four I2C commands.

1. Write the data 0x62 to the I2C register I2CKeyMsb. Terminate the I2C write by a STOP.

2. Write the data 0x9D to the I2C register I2CKeyLsb. Terminate the I2C write by a STOP.

3. Write the data 0xA5 to the I2C register I2CSpmBaseAddr. Terminate the I2C write by a STOP.

4. Write the data 0x5A to the I2C register I2CSpmBaseAddr. Terminate the I2C write by a STOP.

This is illustrated in Figure 57.

SSA 00x0EA0xA5A PA

S : Star t c o nd ition

SA : Slave address

A : Slave acknowledge

P : Stop c onditi on

From master to slave

From slave to master

SSA 00x0EA0x5AA PA

SSA 00xAC

A0x62A PA

SSA 00xADA0x9DA PA

Figure 57: NVM burn proce dur e

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7 AP PLICATION INFORMATION

A typical application schematic is shown in Figure 58.

Figure 58 Typical Application

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8 PACKAGING INFORMATION

8.1 Package Outline Drawing

SX8648 is assembled in a MLPQ-UT28 package as shown in Figure 59.

INDICATOR

(LASER MARK)

PIN 1

DIMENSIONS

NOM

INCHES

bbb

aaa

DIM

MIN MAX

MILLIMETERS

MINMAX NOM

.154 .157 .161 3.90 4.00 4.10

.003

.006

.100

.008

.104

.000

.020

(.006)

0.08

0.20

.010

.108

0.15

2.55

.024

.001 0.00

0.50

2.75

0.25

2.65

0.02

0.60

(0.152)

.004 0.10

2.55 2.65 2.75

0.40 BSC.016 BSC 0.30.012 .020.016 0.40 0.50

.108.104.100

SEATING

PLANE

CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).

COPLANARITY APPL IES TO TH E EXPOSED PAD AS WELL AS THE TERMINALS.

NOTES:

aaa C

LxN

E/2

bbb CAB

D/2 bxN

Figure 59 Package Outline Drawing

8.2 Land Pattern

The land pattern of MLPQ-UT28 package, 4 mm x 4 mm is shown in Figure 60.

Figure 60 Land Pattern

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Contact Infor mation

ll rights reserved. Reproduction in whole or in part is prohibited without the prior written consent of the

believed to be accurate and reliable and may be changed without notice. No liability will be accepted by the

publisher for any consequence of its use. Publication thereof does not convey nor imply any license under

patent or other industrial or intellectual property rights. Semtech assumes no responsibility or liability

whatsoever for any failure or unexpected operation resulting from misuse, neglect improper installation, repair

or improper handling or unusual physical or electrical stress including, but not limited to, exposure to

parameters beyond the specified maximum ratings or operation outside the specified range.

SEMTECH PRODUCTS ARE NOT DESIGNED, INTENDED, AUTHORIZED OR WARRANTED TO BE

SUITABLE FOR USE IN LIFE-SUPPORT APPLICATIONS, DEVICES OR SYSTEMS OR OTHER CRITICAL

PPLICATIONS. INCLUSION OF SEMTECH PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO

BE UND ERT AKE N SO LE L Y AT THE CU STOMER’ S OWN RISK. Sho uld a c us t omer pur c hase or us e Semtech

products f or an y such unaut horized a pplicat ion, the c ustom er shall ind em nif y and hold Sem tech and its officer s,

employees, subsidiaries, affiliates, and distributors harmless against all claims, costs damages and attorney

fees which could arise.

Semtech Corporation

Advanced Communications and Sensing Products Division

200 Flynn Road, Camarillo, CA 93012

Phone: (805) 498-2111 Fax: (805) 498-3804

Mouser Electronics

Authorized Distributor

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