SEMTECH SX8645

SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
GENERAL DESCRIPTION
KEY PRODUCT FEATURES
The SX8645 is an ultra low power, fully integrated
12-channel solution for capacitive touch-buttons and
wheel applications. Unlike many capacitive touch
solutions, the SX8645 features dedicated capacitive
sense inputs (that requires no external components)
in addition to 8 general purpose I/O ports (GPIO).
Each GPIO is typically configured as LED driver with
independent PWM source for enhanced lighting
control such as intensity and fading.
 Complete Twelve Sensors Capacitive Touch Controller for
Buttons and Wheel
ƒ Pre-configured for 6 Buttons and a Wheel
ƒ 8 LED Drivers with Individual Intensity, Fading Control
and Autolight Mode
ƒ 256 steps PWM Linear and Logarithmic control
 High Resolution Capacitive Sensing
ƒ Up to 100pF of Offset Capacitance Compensation at
Full Sensitivity
The SX8645 includes a capacitive 10 bit ADC analog
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.
ƒ Capable of Sensing through Overlay Materials up to
5mm thick
 Extremely Low Power Optimized for Portable Application
ƒ 8uA (typ) in Sleep Mode
ƒ 80uA (typ) in Doze Mode (Scanning Period 195ms)
ƒ 220uA (typ) in Active Mode (Scanning Period 30ms)
 Programmable Scanning Period from 15ms to 1500ms
The SX8645 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.
 Auto Offset Compensation
ƒ Eliminates False Triggers due to Environmental
Factors (Temperature, Humidity)
ƒ Initiated on Power-up and Configurable Intervals
 Multi-Time In-Field Programmable Firmware Parameters
for Ultimate Flexibility
ƒ On-chip user programmable memory for fast, self
contained start-up
The SX8645 supports the 400 kHz I²C serial bus
data protocol and includes a field programmable
slave address. The tiny 5mm x 5mm footprint makes
it an ideal solution for portable, battery powered
applications where power and density are at a
premium.
 "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
TYPICAL APPLICATION CIRCUIT
APPLICATIONS
 Notebook/Netbook/Portable/Handheld computers
 Cell phones, PDAs
 Consumer Products, Instrumentation, Automotive
 Mechanical Button Replacement
ORDERING INFORMATION
Part Number
Temperature
Range
Package
SX8645I05AWLTRT1 -40°C to +85°C Lead Free MLPQ-W32
1
3000 Units/reel
* This device is RoHS/WEEE compliant and Halogen Free
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
Table of Contents
GENERAL DESCRIPTION ........................................................................................................................ 1
TYPICAL APPLICATION CIRCUIT ............................................................................................................ 1
KEY PRODUCT FEATURES..................................................................................................................... 1
APPLICATIONS....................................................................................................................................... 1
ORDERING INFORMATION...................................................................................................................... 1
1
GENERAL DESCRIPTION............................................................................................................... 4
1.1
1.2
1.3
1.4
1.5
2
Pin Diagram
Marking information
Pin Description
Simplified Block Diagram
Acronyms
4
4
5
6
6
ELECTRICAL CHARACTERISTICS ................................................................................................. 7
2.1
2.2
2.3
2.4
3
Absolute Maximum Ratings
Recommended Operating Conditions
Thermal Characteristics
Electrical Specifications
7
7
7
8
FUNCTIONAL DESCRIPTION ........................................................................................................ 10
3.1
3.2
Quickstart Application
Introduction
3.2.1
General
3.2.2
GPIOs
3.2.3
Parameters
3.2.4
Configuration
3.3
Scan Period
3.4
Operation modes
3.5
Sensors on the PCB
3.6
Button and Wheel Information
3.6.1
Button Information
3.6.2
Wheel Information
3.7
Analog Sensing Interface
3.8
Offset Compensation
3.9
Processing
3.10
Configuration
3.11
Power Management
3.12
Clock Circuitry
3.13
I2C interface
3.14
Reset
3.14.1 Power up
3.14.2 RESETB
3.14.3 Software Reset
3.15
Interrupt
3.15.1 Power up
3.15.2 Assertion
3.15.3 Clearing
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
3.15.4 Example
3.16
General Purpose Input and Outputs
3.16.1 Introduction and Definitions
3.16.2 GPI
3.16.3 GPP
3.16.4 GPO
3.16.5 Intensity index vs PWM pulse width
3.17
Smart Wake Up
4
DATASHEET
25
25
25
26
26
27
30
31
PIN DESCRIPTIONS ..................................................................................................................... 32
4.1
4.2
4.3
4.4
4.5
5
Introduction
ASI pins
Host interface pins
Power management pins
General purpose IO pins
32
32
33
36
37
DETAILED CONFIGURATION DESCRIPTIONS .............................................................................. 38
5.1
5.2
5.3
5.4
5.5
5.6
5.7
6
Introduction
General Parameters
Capacitive Sensors Parameters
Button Parameters
Wheel Parameters
Mapping Parameters
GPIO Parameters
38
41
42
47
51
55
58
I2C INTERFACE ........................................................................................................................... 62
6.1
6.2
6.3
6.4
6.5
6.6
I2C Write
I2C read
I2C Registers Overview
Status Registers
Control Registers
SPM Gateway Registers
6.6.1
SPM Write Sequence
6.6.2
SPM Read Sequence
6.7
NVM burn
62
63
64
65
68
70
71
72
73
7
APPLICATION INFORMATION ...................................................................................................... 74
8
PACKAGING INFORMATION ........................................................................................................ 75
8.1
8.2
Package Outline Drawing
Land Pattern
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
1 GENERAL DESCRIPTION
cap1
cap0
vana
resetb
gnd
vdig
gpio7
gpio6
Pin Diagram
32
31
30
29
28
27
26
25
24
gnd
23
gpio5
22
gpio4
21
gpio3
5
20
gpio2
cap7
6
19
gnd
cap8
7
18
gpio1
cap9
8
17
gpio0
4
cap6
Top View
bottom ground pad
9
10
11
12
13
14
15
16
sda
cap5
scl
3
intb
cap4
SX8645
vdd
2
cp
cap3
cn
1
cap11
cap2
cap10
1.1
Figure 1 Pinout Diagram
1.2
Marking information
SX8645
yyww
xxxxxx
R05
yyww = Date Code
xxxxxx = Semtech lot number
R05 = Semtech Code
Figure 2 Marking Information
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
1.3
DATASHEET
Pin Description
Number
Name
Type
Description
1
CAP2
Analog
Capacitive Sensor 2
2
CAP3
Analog
Capacitive Sensor 3
3
CAP4
Analog
Capacitive Sensor 4
4
CAP5
Analog
Capacitive Sensor 5
5
CAP6
Analog
Capacitive Sensor 6
6
CAP7
Analog
Capacitive Sensor 7
7
CAP8
Analog
Capacitive Sensor 8
8
CAP9
Analog
Capacitive Sensor 9
9
CAP10
Analog
Capacitive Sensor 10
10
CAP11
Analog
Capacitive Sensor 11
11
CN
Analog
Integration Capacitor, negative terminal (1nF between CN and CP)
12
CP
Analog
Integration Capacitor, positive terminal (1nF between CN and CP)
13
VDD
Power
Main input power supply
14
INTB
Digital Output
Interrupt, active LOW, requires pull up resistor (on host or external)
15
SCL
Digital Input
I2C Clock, requires pull up resistor (on host or external)
16
SDA
Digital Input/Output
I2C Data, requires pull up resistor (on host or external)
17
GPIO0
Digital Input/Output
General Purpose Input/Output 0
18
GPIO1
Digital Input/Output
General Purpose Input/Output 1
19
GND
Ground
Ground
20
GPIO2
Digital Input/Output
General Purpose Input/Output 2
21
GPIO3
Digital Input/Output
General Purpose Input/Output 3
22
GPIO4
Digital Input/Output
General Purpose Input/Output 4
23
GPIO5
Digital Input/Output
General Purpose Input/Output 5
24
GND
Ground
Ground
25
GPIO6
Digital Input/Output
General Purpose Input/Output 6
26
GPIO7
Digital Input/Output
General Purpose Input/Output 7
27
VDIG
Analog
Digital Core Decoupling, connect to a 100nF decoupling capacitor
28
GND
Ground
Ground
29
RESETB
Digital Input
Active Low Reset. Connect to VDD if not used.
30
VANA
Analog
Analog Core Decoupling, connect to a 100nF decoupling capacitor
31
CAP0
Analog
Capacitive Sensor 0
32
CAP1
Analog
Capacitive Sensor 1
Ground
Exposed pad connect to ground
bottom plate GND
Table 1 Pin description
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
1.4
DATASHEET
Simplified Block Diagram
gpio6
gpio7
vdig
gnd
resetb
vana
cap0
cap1
The simplified block diagram of the SX8645 is illustrated in Figure 3.
SX8645
cap2
cap3
analog
sensor
interface
clock
generation
RC
PWM
LED
controller
gnd
gpio5
gpio4
cap4
power management
cap5
cap6
cap7
cap8
gpio3
micro
processor
GPIO
controller
RAM
NVM
ROM
I2C
gpio2
gnd
gpio1
gpio0
cap9
sda
scl
intb
vdd
cp
cn
cap11
cap10
bottom plate
Figure 3 Simplified block diagram of the SX8645
1.5
ASI
DCV
GPI
GPO
GPP
MTP
NVM
PWM
QSM
SPM
Acronyms
Analog Sensor Interface
Digital Compensation Value
General Purpose Input
General Purpose Output
General Purpose PWM
Multiple Time Programmable
Non Volatile Memory
Pulse Width Modulation
Quick Start Memory
Shadow Parameter Memory
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
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
ESDHBM
3
kV
ILU
± 100
mA
ESD HBM (Human Body model)
Latchup
(i)
(ii)
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
100
mV
Supply Voltage Drop
(iii, iv, v)
VDDdrop
Supply Voltage for NVM programming
VDD
3.0V
3.6
V
Ambient Temperature Range
TA
-40
85
°C
Table 3 Recommended Operating 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 SX8645 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 SX8645 and assures that parameters are re-written into the SPM (should these differ to the parameters held in NVM).
2.3
Thermal Characteristics
Parameter
Thermal Resistance - Junction to Ambient
Symbol
(vi)
θJA
Min.
Max.
Unit
25
°C/W
Table 4 Thermal Characteristics
(vi) Static airflow
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
2.4
DATASHEET
Electrical Specifications
All values are valid within the operating conditions unless otherwise specified.
Parameter
Symbol
Conditions
Active mode, average
IOP,active
Doze mode, average
Sleep
Min.
Typ.
Max.
Unit
30ms scan period,
12 sensors enabled,
minimum sensitivity
220
300
uA
IOP,Doze
195ms scan period,
12 sensors enabled,
minimum sensitivity
80
110
uA
IOP,sleep
I2C and GPI listening,
sensors disabled
8
17
uA
Current consumption
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
Output logic high
VOH
IOH <4mA
Output logic low
VOL
IOL,GPIO<12mA
IOL,SDA,INTB<4mA
0.4
V
tpor
time between rising edge
VDD and rising INTB
150
ms
GPIO set as Output, INTB, SDA
VDD-0.4
V
Start-up
Power up time
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 Electrical Specifications
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
Parameter
I2C Timing Specifications
Symbol
Conditions
DATASHEET
Min.
Typ.
Max.
Unit
400
KHz
(i)
SCL clock frequency
fSCL
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
tBUF
500
us
Input glitch suppression
tSP
50
ns
Table 6 I2C Timing 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 timing
Figure 5 I2C Data timing
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
3 FUNCTIONAL DESCRIPTION
3.1
Quickstart Application
The SX8645 is preconfigured (Quickstart Application) for an application with 6 buttons, a wheel (consisting of 6
sensors) and 8 LED drivers using logarithmic PWM fading.
Implementing a schematic based on Figure 6 will be immediately operational after powering without programming
the SX8645 (even without host).
d7
gpio6
gpio7
vdig
gnd
vana
cap1
resetb
cap0
d0
d1
cap2
SX8645
d2
cap3
d3
cap4
analog
sensor
interface
clock
generation
RC
PWM
LED
controller
d4
d6
gnd
gpio5
d5
gpio4
d4
cap5
d5
power management
gpio3
micro
processor
GPIO
controller
RAM
NVM
ROM
I2C
cap6
d6
d7
cap7
cap8
cap9
d2
gnd
gpio1
d1
gpio0
d0
sda
scl
intb
cp
vdd
bottom plate
cn
cap10
cap11
d3
gpio2
HOST
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.
All other sensors (CAP1 to CAP5) have their own LED associated on a GPIO pin showing a touch or a release.
The sensors on CAP6 to CAP11 are used in a wheel configuration. A moving finger on the wheel will enable the
LED on GPIO6 or GPIO7 indicating the finger rotation direction.
The sensor detection and the LED fading described above are operational without any host interaction.
This is made possible using the SX8645 Autolight feature described in the following sections.
3.2
3.2.1
Introduction
General
The SX8645 is intended to be used in applications which require capacitive sensors covered by isolating overlay
material. A finger approaching the capacitive sensors will change the charge that can be loaded on the sensors.
The SX8645 measures the change of charge and converts that into digital values (ticks). The larger the charge on
the sensors, the larger the number of ticks will be. The charge to ticks conversion is done by the SX8645 Analog
Sensor Interface (ASI).
The ticks are further processed by the SX8645 and converted in a high level, easy to use information for the
user’s host.
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
The information between SX8645 and the user’s host is passed through the I2C interface with an additional
interrupt signal indicating that the SX8645 has new information. For buttons this information is simply touched or
released.
3.2.2
GPIOs
A second path of feedback to the user is using General Purpose Input Output (GPIO) pins. The SX8645 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 SX8645 has eight individual PWM generators, one for each GPIO pin.
The LED fading can be initiated automatically by the SX8645 by setting the SX8645 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 Autolight feature is disabled then the host will decide to start a LED fading-in period, simply by setting
the GP0 pin to ‘high’ using one I2C command. The SX8645 will then slowly fade-in the LED using the PWM
autonomously.
In case the host needs to have full control of the LED intensity then the host can set the GPIO in GPP mode. The
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 SX8645 has many low level built-in, fixed algorithms and procedures. To allow a lot of freedom for the user
and adapt the SX8645 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 wheel, which GPIO is used for outputs or LEDs and which GPIO is
mapped to which button.
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
SX8645 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 SX8645. The programming needs to be done once (over the I2C). The SX8645 will then
boot up from the NVM and additional parameters from the host are not required anymore.
In case the host desires to overwrite the boot-up NVM parameters (partly or even complete) this can be done by
additional I2C communications.
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
3.3
DATASHEET
Scan Period
The basic operation Scan period of the SX8645 sensing interface can be split into three periods over time.
In the first period (Sensing) the SX8645 is sensing all enabled CAP inputs, from CAP0 towards CAP11.
In the second period (Processing) the SX8645 processes the sensor data, verifies and updates the GPIO and I2C
status registers.
In the third period (Timer) the SX8645 is set in a low power mode and waits until a new cycle starts.
Figure 7 shows the different SX8645 periods over time.
Figure 7 Scan Period
The scan period determines the minimum reaction time of the SX8645. The scan period can be configured by the
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 SX8645
generates the interrupt on the INTB pin. The shorter the scan period the faster the reaction time will be.
Very low power consumption can be obtained by setting very long scan periods with the expense of having longer
reaction times.
Important: All external events like GPIO, I2C and INTB are updated in the processing period, so once every scan
period. If e.g. a GPI would change state directly after the processing period then this will be reported with a delay
of one scan period later in time.
3.4
Operation modes
The SX8645 has 3 operation modes. The main difference is found in the reaction time (corresponding to the scan
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 SX8645 OFF, except for the I2C and GPI peripheral, minimizing operating current while
maintaining the power supplies. In Sleep mode the SX8645 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 most applications the reaction time needs to be fast when fingers are present, but can be slow when no person
uses the application. In case the SX8645 is not used for a specific time it can go from Active mode into Doze
mode and power will be saved. This time-out is determined by the Passive Timer which can be configured by the
user or turned OFF if not required.
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
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 SX8645 offers therefore a smart wake-up sequence feature in which the user needs to touch and release a
correct sequence of buttons before Active mode will be entered. This is explained in more detail in the Wake-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 SX8645.
The diagram in Figure 8 shows the available operation modes and the possible transitions.
Figure 8 Operation modes
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3.5
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Sensors on the PCB
The capacitive sensors are relatively simple copper areas on the PCB connected to the twelve SX8645 capacitive
sensor input pins (CAP0…CAP11).The sensors are covered by isolating overlay material (typically 1mm...3mm).
The area of a sensor is typically one square centimeter which corresponds about to the area of a finger touching
the overlay material.
The capacitive sensors can be setup as ON/OFF buttons (see example Figure 9) or arranged in a wheel
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 wheel using six sensors (surrounded by ground plane)
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3.6
3.6.1
DATASHEET
Button and Wheel Information
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 hysteresis. The hysteresis around
the threshold avoids rapid touch and release signaling during transients.
3.6.2 Wheel Information
In case sensors are arranged in a wheel configuration the ON, OFF information remains available as if it would be
a single sensor button.
Figure 12 Wheel ON, OFF
Wherever the wheel is touched the information will be set to ON. If no finger is present the wheel information will
be OFF.
Due to the 2 dimensional character of the wheel 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 wheel.
Interpolation between sensors increases the resolution beyond the number of sensors in the wheel.
The interpolation can be done already on the PCB sensor structures (analog, like the wheel in Figure 10) and as
well by SX8645 digital processing of the ticks using center of gravity calculations.
The position of the finger on the PCB structures varies between the minimum zero and a user defined maximum
(Figure 13).
m
ax
m
in
....x...
position
Figure 13 Wheel Position
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The position belonging to the minimum and associated to a sensor is defined arbitrarily. The SX8645 defines the
minimum position to the sensor with the lowest CAP pin index. E.g. if CAP0 is a button (or disabled) and CAP1 to
CAP7 are the sensors of the wheel then the position ‘zero’ starts at CAP1 and the maximum is found at CAP7.
In addition to the wheel position, the SX8645 allows to detect finger rotation. The rotation occurs if the finger
position changes a certain step size between two succeeding scan periods. A very slow moving finger will not be
considered as a rotation as the changing position will be minor. The SX8645 allows detecting a rotate clockwise
(direction min to max) (see Figure 14) and a rotate counter clockwise (direction max to min) (see Figure 15).
rotate clockwise
Figure 14 Wheel rotate clockwise
Figure 15 Wheel rotate counter clockwise
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3.7
DATASHEET
Analog Sensing Interface
The Analog Sensing Interface (ASI) converts the charge on the sensors into ticks which will be further digitally
processed. The basic principle of the ASI will be explained in this section.
The ASI consists of a multiplexer selecting the sensor, analog switches, a reference voltage, an ADC sigma delta
converter, an offset compensation DAC and an external integration capacitor (see Figure 16).
ASI
cap0
cap1
analog
multiplexor
processing
voltage
reference
switches
cap2
ticks (raw)
ticks-diff
ADC
cap9
low pass
ticks-ave
cap10
Offset
compensation
DAC
cap11
compensation DCV
Cint
Figure 16 Analog Sensor Interface
To get the ticks representing the charge on a specific sensor the ASI will execute several steps.
The charge on a sensor cap (e.g. CAP0) will be accumulated multiple times on the external integration capacitor,
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-up.
The difference between the DAC output and the charge on Cint is the desired signal. In the ideal case the
difference of charge will be converted to zero ticks if no finger is present and the number of ticks becomes 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 SX8645 allows setting the sensitivity for each sensor individually in applications which have a variety of
sensors sizes or different overlays or for fine-tuning performances. The optimal sensitivity is depending heavily on
the final application. If the sensitivity is too low the ticks will not pass the thresholds and it is not possible to detect
fingers. In case the sensitivity is set too large a finger hovering above the sensors will already be detected before
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
DATASHEET
Offset Compensation
The capacitance at the CAP pins is determined by an intrinsic capacitance of the integrated circuit, the PCB
traces, ground coupling and the sensor planes. This capacitance is relatively large and might become easily some
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 capacitance. This would require a very precise, high resolution ADC and complicated, power consuming,
digital processing.
The SX8645 features a 16 bit DAC which compensates for the large, slow varying capacitance already in front 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 SX8645 the Digital Compensation Values (DCV) are estimated by the digital processing
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 SX8645 is shut down the compensation values will be lost. At a next power-up the procedure starts all over
again. This assures that the SX8645 will operate under any condition. Powering up at e.g. different temperatures
will not change the performance of the SX8645 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 SX8645 will initiate a compensation procedure
and find a new set of DCVs.
Compensation procedures can as well be initiated by the SX8645 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.
Finally the host can initiate a compensation procedure by using the I2C interface (in Active or Doze mode). This is
e.g. required after the host changed the sensitivity of sensors.
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3.9
DATASHEET
Processing
The first processing step of the raw ticks, coming out of the ASI, is low pass filtering to obtain an estimation of the
average capacitance: tick-ave (see Figure 17).
This slowly varying average is important in the detection of slowly changing environmental changes.
ASI
processing
SPM
processing
ticks (raw)
tick-diff
PWM LED
controller
tick-ave
GPIO
controller
low pass
I2C
compensation DCV
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 tick-diff, tick-ave and the configuration parameters in the SPM are then processed and determines the sensor
information, I2C registers status and PWM control.
3.10 Configuration
Figure 18 shows the building blocks used for configuring the SX8645.
Figure 18 Configuration
The default configuration parameters of the SX8645 are stored in the Quick Start Memory (QSM). This
configuration data is setup to a very common application for the SX8645 with 6 buttons and a wheel. Without any
programming or host interaction the SX8645 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 SX8645 can be setup and/or
programmed over the I2C interface.
The configuration parameters of the SX8645 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 SX8645 checks if the NVM contains valid data. In that case the configuration parameter source
becomes the NVM. If the NVM is empty or non-valid then the configuration source becomes the QSM. In the next
step the SX8645 copies the configuration parameter source (QSM or NVM) into the Shadow Parameter Memory
(SPM). The SX8645 is operational and uses the configuration parameters of the SPM.
During power down or reset event the SPM loses all content. It will automatically be reloaded (from QSM or NVM)
following power up or at the end of the reset event.
The host will interface with the SX8645 through the I2C bus.
The I2C of the SX8645 consists of 16 registers. Some of these I2C registers are used to read the status and
information of the button and the wheel. Other I2C registers allow the host to take control of the SX8645. The 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 development phases of the application where the configuration parameters are not yet fully defined and
as well during the operation of the application if some parameters need to be changed dynamically.
Figure 19 Host SPM mode
The content of the SPM remains valid as long as the SX8645 is powered and no reset is performed. After a power
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 SX8645 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 parameter set is determined this can be written to the NVM over the I2C using the 2 steps approach 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 SX8645 uses on-chip voltage regulators which are controlled by the on-chip microprocessor. 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 SX8645 internal circuitry and must not be loaded
externally.
3.12 Clock Circuitry
The SX8645 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 SX8645.
The I2C slave implemented on the SX8645 is compliant with the standard (100kb/s) and fast mode (400kb/s)
The default SX8645 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 SX8645 is then ready for operation.
Figure 21 Power Up vs. INTB
During the power on period the SX8645 stabilizes the internal regulators, RC clocks and the firmware initializes all
registers.
During the power up the SX8645 is not accessible and I2C communications are forbidden.
As soon as the INTB rises the SX8645 will be ready for I2C communication.
3.14.2 RESETB
When RESETB is driven low the SX8645 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 Hardware 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 SX8645 is then ready for operation.
Figure 24 Power Up vs. INTB
During the power on period the SX8645 stabilizes the internal regulators, RC clocks and the firmware initializes all
registers.
During the power up the SX8645 is not accessible and I2C communications are forbidden.
As soon as the INTB rises the SX8645 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 event occurred (touch or release if enabled). I2C registers CapStatMsb and CapStatLsb show the
detailed status of the Buttons,
• if a Wheel event occurred (touch, release, rotate clockwise, rotate counter clockwise or position change). I2C
registers CapStatMsb, WhlPosMsb and WhlPosLsb show the detailed status of the Wheel,
• if a GPI edge occurred (rising or falling if enabled). I2C register GpiStat shows the detailed status 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 SX8645 will assert the interrupt (1). The host will read the IrqSrc information over
the I2C and this clears the interrupt (2).
If the finger releases the button the interrupt will be asserted (3). The host reading the IrqSrc information 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 SX8645 offers eight General Purpose Input and Outputs (GPIO) pins which can be configured 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 polarity of the GPP and GPO pins is defined as in figure below, driving an LED as example. It has to be set
accordingly in SPM parameter GpioPolarity.
Figure 26 Polarity definition, (a) normal, (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.
SPM
I2C
GpioMode
GpioPullUpDown
GpioInterrupt
GpioDebounce
IrqSrc[4]
GpiStat
GPI
X
X
X
X
X
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 control 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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SPM
I2C
GpioMode
GpioOutPwrUp
GpioPolarity
GpioIntensityOn
GpioIntensityOff
GpioFunction
GppPinId
GppIntensity
DATASHEET
GPP
X
1
X
X
1
X
1
X
X
X
1
X
1
At power up, GppIntensity of each GPP pin is initialized with GpioIntensityOn or GpioIntensityOff depending on GpioOutPwrUp
corresponding bits value.
Table 8 SPM/I2C 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. Typical 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 Control in GPO mode, Autolight OFF
Figure 30 LED Control in GPO mode, Autolight ON (mapped to Button)
Additionally these transitions can be configured to be done with or without fading following 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 (LED fade in), inverted polarity, (a) linear, (b) logarithmic
The fading out (e.g. after a button is released) is identical to the fading in but an additional off delay can be added
before the fading starts (Figure 33 and Figure 34).
Figure 33 GPO OFF transition (LED fade out), normal polarity, (a) linear, (b) logarithmic
Figure 34 GPO OFF transition (LED fade out), inverted polarity, (a) linear, (b) logarithmic
Please note that standard high/low logic signals are just a specific case of GPO mode and can also be generated
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.
SPM
I2C
1
2
GpioMode
GpioOutPwrUp
GpioAutoligth
GpioPolarity
GpioIntensityOn
GpioIntensityOff
GpioFunction
GpioIncFactor
GpioDecFactor
GpioIncTime
GpioDecTime
GpioOffDelay
GpoCtrl
GPO
X
1
X
X
X
X
X
X
X
X
X
X
X
2
X
Only if Autolight is OFF, else must be left to 0 (default value)
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
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Lin/Log
0/0
2/0
3/0
4/0
5/0
6/2
7/2
8/2
9/2
10/2
11/2
12/2
13/2
14/2
15/3
16/3
17/3
18/3
19/3
20/3
21/3
22/3
23/3
24/4
25/4
26/4
27/4
28/4
29/4
30/4
31/4
32/5
Index
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
Lin/Log
33/5
34/5
35/5
36/5
37/5
38/6
39/6
40/6
41/6
42/6
43/7
44/7
45/7
46/7
47/7
48/8
49/8
50/8
51/8
52/9
53/9
54/9
55/9
56/10
57/10
58/10
59/10
60/11
61/11
62/11
63/12
64/12
Index
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
Lin/Log
65/12
66/13
67/13
68/13
69/14
70/14
71/14
72/15
73/15
74/15
75/16
76/16
77/16
78/17
79/17
80/18
81/18
82/19
83/19
84/20
85/20
86/21
87/21
88/22
89/22
90/23
91/23
92/24
93/24
94/25
95/25
96/26
Index
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
Lin/Log
97/26
98/27
99/27
100/28
101/29
102/29
103/30
104/30
105/31
106/32
107/32
108/33
109/33
110/34
111/35
112/35
113/36
114/37
115/38
116/38
117/39
118/40
119/40
120/41
121/42
122/43
123/44
124/44
125/45
126/46
127/47
128/48
Index
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
Lin/Log
129/48
130/49
131/50
132/51
133/52
134/53
135/54
136/55
137/55
138/56
139/57
140/58
141/59
142/60
143/61
144/62
145/63
146/64
147/65
148/66
149/67
150/68
151/69
152/71
153/72
154/73
155/74
156/75
157/76
158/77
159/78
160/80
Index
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
Lin/Log
161/81
162/82
163/83
164/84
165/86
166/87
167/88
168/89
169/91
170/92
171/93
172/95
173/96
174/97
175/99
176/100
177/101
178/103
179/104
180/106
181/107
182/109
183/110
184/111
185/113
186/114
187/116
188/117
189/119
190/121
191/122
192/124
Index
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
Lin/Log
193/125
194/127
195/129
196/130
197/132
198/133
199/135
200/137
201/139
202/140
203/142
204/144
205/146
206/147
207/149
208/151
209/153
210/155
211/156
212/158
213/160
214/162
215/164
216/166
217/168
218/170
219/172
220/174
221/176
222/178
223/180
224/182
Index
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
Lin/Log
225/184
226/186
227/188
228/190
229/192
230/194
231/197
232/199
233/201
234/203
235/205
236/208
237/210
238/212
239/215
240/217
241/219
242/221
243/224
244/226
245/229
246/231
247/233
248/236
249/238
250/241
251/243
252/246
253/248
254/251
255/253
256/256
Lin/Log
64/131
63/129
62/127
61/126
60/124
59/123
58/121
57/119
56/117
55/116
54/114
53/112
52/110
51/109
50/107
49/105
48/103
47/101
46/100
45/98
44/96
43/94
42/92
41/90
40/88
39/86
38/84
37/82
36/80
35/78
34/76
33/74
Index
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
Lin/Log
32/72
31/70
30/68
29/66
28/64
27/62
26/59
25/57
24/55
23/53
22/50
21/48
20/46
19/44
18/41
17/39
16/37
15/35
14/32
13/30
12/27
11/25
10/23
9/20
8/18
7/15
6/13
5/10
4/8
3/5
2/3
0/0
Table 10 Intensity index vs. PWM pulse width (normal polarity)
Index
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Lin/Log
256/256
255/256
254/256
253/256
252/256
251/254
250/254
249/254
248/254
247/254
246/254
245/254
244/254
243/254
242/253
241/253
240/253
239/253
238/253
237/253
236/253
235/253
234/253
233/252
232/252
231/252
230/252
229/252
228/252
227/252
226/252
225/251
Index
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
Lin/Log
224/251
223/251
222/251
221/251
220/251
219/250
218/250
217/250
216/250
215/250
214/249
213/249
212/249
211/249
210/249
209/248
208/248
207/248
206/248
205/247
204/247
203/247
202/247
201/246
200/246
199/246
198/246
197/245
196/245
195/245
194/244
193/244
Index
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
Lin/Log
192/244
191/243
190/243
189/243
188/242
187/242
186/242
185/241
184/241
183/241
182/240
181/240
180/240
179/239
178/239
177/238
176/238
175/237
174/237
173/236
172/236
171/235
170/235
169/234
168/234
167/233
166/233
165/232
164/232
163/231
162/231
161/230
Index
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
Lin/Log
160/230
159/229
158/229
157/228
156/227
155/227
154/226
153/226
152/225
151/224
150/224
149/223
148/223
147/222
146/221
145/221
144/220
143/219
142/218
141/218
140/217
139/216
138/216
137/215
136/214
135/213
134/212
133/212
132/211
131/210
130/209
129/208
Index
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
Lin/Log
128/208
127/207
126/206
125/205
124/204
123/203
122/202
121/201
120/201
119/200
118/199
117/198
116/197
115/196
114/195
113/194
112/193
111/192
110/191
109/190
108/189
107/188
106/187
105/185
104/184
103/183
102/182
101/181
100/180
99/179
98/178
97/176
Index
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
Lin/Log
96/175
95/174
94/173
93/172
92/170
91/169
90/168
89/167
88/165
87/164
86/163
85/161
84/160
83/159
82/157
81/156
80/155
79/153
78/152
77/150
76/149
75/147
74/146
73/145
72/143
71/142
70/140
69/139
68/137
67/135
66/134
65/132
Index
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
Table 11 Intensity 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 SX8645 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 full correct wake-up sequence is entered, the SX8645 will remain in Doze mode. Any wrong 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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Ultra Low Power, Capacitive Button and Wheel
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4 PIN DESCRIPTIONS
4.1
Introduction
This chapter describes briefly the pins of the SX8645, 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, ..., CAP11
The capacitance sensor pins (CAP0, CAP1, ..., CAP11) 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, ..., CAP11 pins.
SX8645
VANA
sensor
CAPx
CAP_INx
ASI
Note : x = 0, 1,2,…11
Figure 35 Simplified diagram of CAP0, CAP1, ..., CAP11
CN, CP
The CN and the CP pins are connected to the ASI circuitry. A 1nF sampling capacitor between CP and CN needs
to be placed as close as possible to the SX8645.
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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SX8645
VANA
CP
ASI
VANA
CN
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
SX8645
R_INT
INTB
to host
INT
Figure 37 Simplified diagram of INTB
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SCL
The SCL pin is a high impedance input pin. The SCL pin is protected to VDD, using dedicated devices, in order 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
SX8645
R_SCL
SCL
SCL_IN
from host
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
SX8645
R_SDA
SDA
SDA_IN
from/to host
SDA_OUT
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
SX8645
R_RESETB
RESETB
RESETB_IN
from host
Figure 40 Simplified diagram of RESETB controlled by host
Figure 41 shows the RESETB without host control.
VDD
SX8645
RESETB
RESETB_IN
Figure 41 Simplified diagram of RESETB without host control
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Ultra Low Power, Capacitive Button and Wheel
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4.4
DATASHEET
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 SX8645.
VDD has protection to GROUND.
Figure 42 shows a simplified diagram of the VDD pin.
SX8645
VDD
VDD
Figure 42 Simplified diagram of VDD
GND
The SX8645 has four ground pins all named GND. These pins and the package center pad need to be connected
to ground potential.
The GND has protection to VDD.
Figure 43 shows a simplified diagram of the GND pin.
SX8645
VDD
GND
GND
Figure 43 Simplified diagram of GND
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Ultra Low Power, Capacitive Button and Wheel
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VANA, VDIG
The SX8645 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.
SX8645
VDD
VDIG
VDIG
Cvdig
GND
VDD
VANA
VANA
Cvana
GND
Figure 44 Simplified diagram of VANA and VDIG
4.5
General purpose IO pins
The SX8645 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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Ultra Low Power, Capacitive Button and Wheel
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5 DETAILED CONFIGURATION DESCRIPTIONS
5.1
Introduction
The SX8645 configuration parameters are taken from the QSM or the NVM and loaded into the SPM as explained
in the chapter ‘functional description’.
This chapter describes the details of the configuration parameters of the SX8645.
.
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,
• Wheel: related to the conversion from sensor data towards wheel information,
• Mapping: related to mapping of button and wheel 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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Ultra Low Power, Capacitive Button and Wheel
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DATASHEET
Name
default QSM
value
Address
Name
0x00
Reserved
0xxx
0x20
Reserved
0x01
Reserved
0xxx
0x21
BtnCfg
0x02
Reserved
0x18
0x22
BtnAvgThresh
0x50
0x03
Reserved
0xxx
0x23
BtnCompNegThresh
0x50
I2CAddress
0x2B
0x24
BtnCompNegCntMax
0x01
ActiveScanPeriod
0x02
0x25
BtnHysteresis
0x0A
DozeScanPeriod
0x0D
0x26
BtnStuckAtTimeout
0x00
PassiveTimer
0x00
0x27
WhlCfg
0x00
0x00
0x28
WhlStuckAtTimeout
0x00
0x05
0x06
General
0x04
0x07
0x08
Reserved
Button
Address
default QSM
value
0x00
0x30
0x01
0x29
WhlHysteresis
0x03
CapMode11_8
0xFF
0x2A
Reserved
0xFF
0x0B
CapMode7_4
0xF5
0x2B
WhlNormMsb
0x01
0x0C
CapMode3_0
0x55
0x2C
WhlNormLsb
0x40
0x0D
CapSensitivity0_1
0x00
0x2D
WhlAvgThresh
0x50
0x0E
CapSensitivity2_3
0x00
0x2E
WhlCompNegThresh
0x50
0x0F
CapSensitivity4_5
0x00
0x2F
WhlCompNegCntMax
0x01
0x10
CapSensitivity6_7
0x00
0x30
WhlRotateThresh
0x02
0x11
CapSensitivity8_9
0x00
0x31
WhlOffset
0x00
CapSensitivity10_11
0x00
0x32
Reserved
0x00
CapThresh0
0xA0
0x33
MapWakeupSize
0x00
CapThresh1
0xA0
0x34
MapWakeupValue0
0x00
CapThresh2
0xA0
0x35
MapWakeupValue1
0x00
0x12
0x13
0x14
0x15
Wheel
CapModeMisc
0x0A
Capacitive Sensors
0x09
0xA0
0x36
MapWakeupValue2
0x00
CapThresh4
0xA0
0x37
MapAutoLight0
0xFE
0x18
CapThresh5
0xA0
0x38
MapAutoLight1
0x54
0x19
CapThresh6
0xA0
0x39
MapAutoLight2
0x32
0x1A
CapThresh7
0xA0
0x3A
MapAutoLight3
0x10
0x1B
CapThresh8
0xA0
0x3B
MapAutoLightGrp0Msb
0x00
0x1C
CapThresh9
0xA0
0x3C
MapAutoLightGrp0Lsb
0x00
0x1D
CapThresh10
0xA0
0x3D
MapAutoLightGrp1Msb
0x00
0x1E
CapThresh11
0xA0
0x3E
MapAutoLightGrp1Lsb
0x00
0x1F
CapPerComp
0x00
0x3F
MapSegmentHysteresis
0x02
Mapping
CapThresh3
0x17
0x16
Table 12 SPM address map: 0x00…0x3F
Note
• ‘0xxx’:
write protected data
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Ultra Low Power, Capacitive Button and Wheel
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Address
Name
default QSM
value
Address
DATASHEET
Name
default QSM
value
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
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
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
0x50
Gpio
GpioMode7_4
Gpio
0x40
0x5E
GpioDecTime5_4
0x44
0x7E
Reserved
0xFF
0x5F
GpioDecTime3_2
0x44
0x7F
SpmCrc*
0xE1
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
DATASHEET
General Parameters
General Parameters
Address
Name
Bits
Description
0x04
I2CAddress
7
Reserved
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 Wheel Information (Figure 8)
0x00: OFF (default)
0x01: 1 second
…
0xFF: 255 seconds
Table 14 General Parameters
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5.3
DATASHEET
Capacitive Sensors Parameters
Capacitive Sensors Parameters
Address
Name
Bits
Description
0x09
CapModeMisc
7:3
Reserved
2
IndividualSensitivity
1:0
Reserved
Reserved: ‘01’
7:6
CAP11 Mode
5:4
CAP10 Mode
3:2
CAP9 Mode
1:0
CAP8 Mode
Defines the mode of
the CAP pin.
00: Disabled
01: Button
10: Reserved
11: Wheel
7:6
CAP7 Mode
5:4
CAP6 Mode
3:2
CAP5 Mode
Button
1:0
CAP4 Mode
Button
7:6
CAP3 Mode
Button
5:4
CAP2 Mode
Button
3:2
CAP1 Mode
Button
1:0
CAP0 Mode
Button
7:4
7:4
CAP0 Sensitivity - Common Sensitivity Defines the sensitivity.
0x0: Minimum (default)
CAP1 Sensitivity
0x7: Maximum
0x8…0xF: Reserved
CAP2 Sensitivity
3:0
CAP3 Sensitivity
7:4
CAP4 Sensitivity
3:0
CAP5 Sensitivity
7:4
CAP6 Sensitivity
3:0
CAP7 Sensitivity
7:4
CAP8 Sensitivity
3:0
CAP9 Sensitivity
7:4
CAP10 Sensitivity
3:0
CAP11 Sensitivity
0x0A
0x0B
0x0C
0x0D
CapMode11_8
CapMode7_4
CapMode3_0
CapSensitivity0_1
3:0
0x0E
0x0F
0x10
0x11
0x12
CapSensitivity2_3
CapSensitivity4_5
CapSensitivity6_7
CapSensitivity8_9
CapSensitivity10_11
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
Revision 7_5, February 10
Defines common sensitivity for all sensors or individual
sensor sensitivity.
0: Common settings (CapSensitivity0_1[7:4])
1: Individual CAP sensitivity settings (CapSensitivityx_x)
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Wheel
Wheel
Wheel
Wheel
Wheel
Default
Wheel
Defines the Touch Threshold ticks.
0x00: 0,
0x01: 4,
…
0xA0: 640 (default),
…
0xFF: 1020
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Capacitive Sensors Parameters
Address
Name
Bits
Description
0x1A
CapThresh7
7:0
CAP7 Touch Threshold
0x1B
CapThresh8
7:0
CAP8 Touch Threshold
0x1C
CapThresh9
7:0
CAP9 Touch Threshold
0x1D
CapThresh10
7:0
CAP10 Touch Threshold
0x1E
CapThresh11
7:0
CAP11 Touch Threshold
0x1F
CapPerComp
7:4
Reserved
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 the ASI is using a common sensitivity for all capacitive sensors as in the usual case overlay material
and sensors sizes are about equal. The register bits CapSensitivity0_1[7:4] determine the sensitivity for all
sensors in common sensitivity mode.
In special applications it might be required to have a different, individual, sensitivity for each CAP pin. This can
be obtained by setting bit CapModeMisc[2]. The individual sensitivity mode results in longer sensing periods
than required in common sensitivity mode.
CapMode11_8, CapMode7_4, CapMode3_0:
The CAP pins can be set as a button, part of a wheel or disabled depending on the application.
minimum
default
maximum
buttons
zero
six
eight
wheel
one
(of four sensors)
one
(of six sensors)
one
(of twelve 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 wheel sensor attribution sequence are allowed, but CAP buttons inside a wheel
are not allowed (see example Figure 47 with CAP3 in a correct and a not allowed configuration).
Figure 47 Button and Wheel good/bad configuration examples (I)
The physical order of the wheel sensors on the PCB should correspond to the incremental CAP pin numbers.
Crossing wheel 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 Wheel good/bad configuration examples (II)
The minimum position of the wheel is associated to the CAP pin, attributed to the wheel, with the lowest index
(in Figure 48 this is CAP2).
The maximum position of the wheel is associated to the CAP pin, attributed to the wheel, with the highest
index (in Figure 48 this is CAP6).
CapSensitivity0_1, CapSensitivity2_3, CapSensitivity4_5,
CapSensitivity6_7, CapSensitivity8_9, CapSensitivity10_11:
The sensitivity of the sensors can be set between 8 values. The higher the sensitivity is set the larger the value
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 sensitivity is identical for all sensors in common sensitivity mode using the bits CapSensitivity0_1[7:4] and
can be set individually using register CapModeMisc[2].
The maximum number of ticks that can be obtained depends on the selected sensitivity as illustrated in Table
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,
CapThresh8, CapThresh9, CapThresh10, CapThresh11:
For each CAP pin a threshold level can be set individually.
The threshold levels are used by the SX8645 for making touch and release decisions on e.g. touch or notouch.
The details are explained in the sections for buttons and wheel.
CapPerComp:
The SX8645 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 wheel and
buttons are released.
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5.4
DATASHEET
Button Parameters
Button Parameters
Address
Name
Bits
Description
0x21
BtnCfg
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 sample (default)
01: 2 samples debounce
10: 3 samples debounce
11: 4 samples debounce
1:0
Defines the number of samples at the scan period for determining a touch
00: OFF, use incoming sample (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 compensation 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 Configuration Parameters
ticks_diff
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.
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 release is detected immediately (BtnCfg [3:2] = 00) at the first sample which is below the threshold minus the
hysteresis.
BtnCfg
The SX8645 can report all touches of multiple fingers or the SX8645 can be set to report only the first detected
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 SX8645 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 SX8645 will start an
offset compensation procedure.
ticks_diff
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.
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 recommended value for this register is ‘1’ which means that the offset compensation starts on the first 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 stuckat timer is set to one second then the touch of a finger will last only for one second and considered
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
DATASHEET
Wheel Parameters
Wheel Parameters
Address
Name
Bits
Description
0x27
WhlCfg
7:4
Reserved
3:2
Defines the number of samples at the scan period for determining a release
00: OFF, use incoming sample (default)
01: 2 samples debounce
10: 3 samples debounce
11: 4 samples debounce
1:0
Defines the number of samples at the scan period for determining a touch
00: OFF, use incoming sample (default)
01: 2 samples debounce
10: 3 samples debounce
11: 4 samples debounce
0x28
WhlStuckAtTimeout
7:0
Defines the stuck at timeout.
0x00: OFF (default)
0x01: 1 second
…
0xFF: 255 seconds
0x29
WhlHysteresis
7:0
Defines the Wheel Touch/Release Hysteresis.
0x00: 0
0x01: 4
…
0x03: 12 (default)
…
0xFF: 1020
0x2B
WhlNormMsb
7:0
Wheel Norm Msb
0x2C
WhlNormLsb
7:0
Wheel Norm Lsb
0x2D
WhlAvgThresh
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
WhlCompNegThresh
7:0
Defines the negative offset compensation threshold.
0x00: 0
0x01: 4
…
0x50: 320 (default)
…
0xFF: 1020
0x2F
WhlCompNegCntMax
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
WhlRotateThresh
7:0
Defines the threshold for detecting a rotate clockwise or counter clockwise.
The threshold is a percentage of the maximum wheel position.
0x00: 0%
…
0x02: 2% (default)
Revision 7_5, February 10
Defines the 16 bits wheel norm (default 0x0140)
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Wheel Parameters
Address
Name
Bits
Description
…
0x64: 100%
A succeeding position difference, at the scan period, above the threshold is
considered as a rotate clockwise or counter clockwise.
Table 19 Wheel Parameters
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The pressure represents the finger touch on the sensors of the wheel and it used to determine if a wheel is
touched or released.
N −1
∑ (ticks _ diff (i) − CapThresh(i))
WhlPressure =
i =0
- 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 wheel status is released.
In case the pressure is larger as the Wheel Hysteresis the wheel status is touched.
The position of a finger on a wheel is calculated by the centre of gravity algorithm.
N −1
WhlPos
WhlNorm
=
32
∗
∑ i * (ticks _ diff (i) − CapThresh (i))
i =0
N −1
∑ (ticks _ diff (i) − CapThresh (i))
i=0
- N is the number of sensors,
- A sensor with ticks smaller than the CapThreshold is not taken into account for calculating the position,
- WhlNorm[15:0] is a 16 bit number determined by WhlNormMsb[15:8] and WhlNormLsb[7:0].
- WhlPos is the wheel position (16 bits) which can be read by the host over the I2C registers WhlPosMsb and
WhlPosLsb
Figure 51 Wheel Position
Figure 51 shows an example of a wheel composed of 6 sensors (CAP0, CAP1… CAP5).
The default wheel norm value 320 (WhlNormMsb = 0x01, WhlNormLsb = 0x40), is taken for the example.
A touch on CAP0 gives the wheel position: 0.
A touch on CAP1 gives the wheel position: 10.
A touch on CAP5 gives the wheel position: 50.
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: 5
Assuming the touch is identically distributed on CAP1 and CAP2 then the position will be: 15
Assuming the touch is identically distributed on CAP4 and CAP5 then the position will be: 55
The minimum position of a wheel equals 0.
The maximum position is obtained if the finger is very slightly on CAP5 and heavily on CAP0.
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The maximum position (WhlPosMax) is defined by:
WhlPosMax =
WhlNorm
×N
32
with:
N is the number of sensors in the wheel
Slow varying wheel ticks due to environmental changes are handled as buttons in the previous section.
If the ticks pass below the wheel negative threshold for more than the compensation negative max counter then
an offset compensation phase will be triggered.
If the ticks pass above the wheel average positive threshold then the averaging filters will be held.
A finger that moves very slowly over the wheel is not considered as a rotation. The status rotate clockwise and
rotate counter clockwise will not be set.
A finger that moves faster on the wheel will change the rotation status.
A rotation is detected if the difference of the position for two succeeding samples at the scanning rate goes
beyond the rotation threshold (WhlRotateThresh). A large rotation threshold requires very rapid finger rotations,
while a small rotation threshold detects more easily rotations but gets sensitive to noise variations as well.
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5.6
DATASHEET
Mapping Parameters
Mapping Parameters
Address
Name
Bits
Description
0x33
MapWakeupSize
7:3
Reserved
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.
0x34
0x35
0x36
0x37
0x38
0x39
0x3A
0x3B
0x3C
MapWakeupValue0
MapWakeupValue1
MapWakeupValue2
MapAutoLight0
MapAutoLight1
MapAutoLight2
MapAutoLight3
MapAutoLightGrp0Msb
MapAutoLightGrp0Lsb
Revision 7_5, February 10
7:4
key5
3:0
key4
7:4
key3
3:0
key2
7:4
key1
3:0
key0
7:4
GPIO[7]
3:0
GPIO[6]
7:4
GPIO[5]
3:0
GPIO[4]
7:4
GPIO[3]
3:0
GPIO[2]
7:4
GPIO[1]
3:0
GPIO[0]
7
Reserved
6
Segment
5
Rotate Clockwise
4
Rotate Counter Clockwise
3
Btn11
2
Btn10
1
Btn9
0
Btn8
7
Btn7
6
Btn6
5
Btn5
4
Btn4
3
Btn3
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Defines the sensor event associated to each key.
0x00: Btn0 (default)
0x01: Btn1
…
0x0B: Btn11
0x0C: Wheel Touch
0x0D: Rotate Counter Clockwise
0x0E: Rotate Clockwise
0x0F: Reserved
Defines the mapping between GPOs (with
Autolight ON) and sensor events.
0x00: Btn0 (default)
0x01: Btn1
…
0x0B: Btn11
0x0C: Group0 as defined by MapAutoLightGrp0
0x0D: Group1 as defined by MapAutoLightGrp1
0x0E: Rotate Counter Clockwise
0x0F: Rotate Clockwise
Several GPOs can be mapped to the same sensor
event and will be controlled simultaneously.
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 wheel event Segment
which is exclusive (ie must be the only one
enabled to be used)
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Mapping Parameters
Address
0x3D
0x3E
0x3F
Name
MapAutoLightGrp1Msb
MapAutoLightGrp1Lsb
MapSegmentHysteresis
Bits
Description
2
Btn2
1
Btn1
0
Btn0
7
Reserved
6
Wheel Touch
5
Rotate Clockwise
4
Rotate Counter Clockwise
3
Btn11
2
Btn10
1
Btn9
0
Btn8
7
Btn7
6
Btn6
5
Btn5
4
Btn4
3
Btn3
2
Btn2
1
Btn1
0
Btn0
7:0
Defines the position hysteresis for detecting a segment change.
The hysteresis is defined as a percentage of the maximum wheel position.
0x00: 0%
…
0x02: 2% (default)
…
0x64: 100%
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.
This hysteresis applies to all segments of the wheel.
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
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- key3 = 0x0
=> MapWakeupValue2 set to 0x06
MapAutoLight0, MapAutoLight1, MapAutoLight2, MapAutoLight3
MapAutoLightGrp0Msb, MapAutoLightGrp0Lsb, MapAutoLightGrp1Msb, MapAutoLightGrp1Lsb
These registers define the mapping between the GPO pins (with Autolight ON) and the sensor information which
will control its ON/OFF state.
The mapping can be done to a specific sensor event but also on groups (in this case any sensor event in the
group will control 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
Wheel Touch
Touch
Release
Rotation Clock Wise
Rotation Clock Counter Wise or Release
Rotation Counter Clock Wise
Rotation Clock Wise or Release
Segment Touched
Segment Released
Wheel Rotation Clock Wise
Wheel Rotation Counter Clock Wise
Wheel Segment
Table 21 Autolight Mapping, Sensor Information
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)
When the Wheel Segment event is mapped, the number of GPOs mapped to it determines the number of
wheel 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 Wheel Segment event then the wheel is split in
two segments. GPO[0] will turn ON for a touch on the wheel segment [0, WhlPosMax/2] and GPO[1] for a
touch on the wheel segment [WhlPosMax/2, WhlPosMax].
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5.7
DATASHEET
GPIO Parameters
GPIO Parameters
Address
Name
Bits Description
0x40
GpioMode7_4
7:6 GPIO[7] Mode
5:4 GPIO[6] Mode
3:2 GPIO[5] Mode
Defines the GPIO mode.
00: GPO (default)
01: GPP
10: GPI
11: Reserved
1:0 GPIO[4] Mode
0x41
GpioMode3_0
7:6 GPIO[3] Mode
5:4 GPIO[2] Mode
3:2 GPIO[1] Mode
1:0 GPIO[0] Mode
0x42
GpioOutPwrUp
7:0 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
GPIO[0] Output Value at Power Up
0x43
GpioAutoLight
7:0 GPIO[7] AutoLight
GPIO[6] AutoLight
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.
Enables Autolight in GPO mode
0 : OFF
1 : ON (default)
GPIO[5] AutoLight
GPIO[4] AutoLight
GPIO[3] AutoLight
GPIO[2] AutoLight
GPIO[1] AutoLight
GPIO[0] AutoLight
0x44
GpioPolarity
7:0 GPIO[7] Output Polarity
GPIO[6] Output Polarity
GPIO[5] Output Polarity
Defines the polarity of the GPO and GPP
pins.
0: Inverted (default)
1: Normal
GPIO[4] Output Polarity
GPIO[3] Output Polarity
GPIO[2] Output Polarity
GPIO[1] Output Polarity
GPIO[0] Output Polarity
0x45
GpioIntensityOn0
0x46
GpioIntensityOn1
0x47
GpioIntensityOn2
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Defines the ON intensity index
0x00: 0
0x01: 1
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GPIO Parameters
Address
Name
0x48
GpioIntensityOn3
0x49
GpioIntensityOn4
0x4A
GpioIntensityOn5
0x4B
GpioIntensityOn6
0x4C
GpioIntensityOn7
0x4D
GpioIntensityOff0
0x4E
GpioIntensityOff1
0x4F
GpioIntensityOff2
0x50
GpioIntensityOff3
0x51
GpioIntensityOff4
0x52
GpioIntensityOff5
0x53
GpioIntensityOff6
0x54
GpioIntensityOff7
0x56
GpioFunction
Bits Description
…
0xFF: 255 (default)
7:0 OFF Intensity Index
Defines the OFF intensity index
0x00: 0 (default)
0x01: 1
…
0xFF: 255
7:0 GPIO[7] Function
Defines the intensity index vs PWM pulse
width function.
0: Logarithmic (default)
1: Linear
GPIO[6] Function
GPIO[5] Function
GPIO[4] Function
GPIO[3] Function
GPIO[2] Function
GPIO[1] Function
GPIO[0] Function
0x57
GpioIncFactor
7:0 GPIO[7] Fading Increment Factor
GPIO[6] Fading Increment Factor
GPIO[5] 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[4] Fading Increment Factor
GPIO[3] Fading Increment Factor
GPIO[2] Fading Increment Factor
GPIO[1] Fading Increment Factor
GPIO[0] Fading Increment Factor
0x58
GpioDecFactor
7:0 GPIO[7] Fading Decrement Factor
GPIO[6] Fading Decrement Factor
GPIO[5] 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
GPIO[4] Fading Decrement Factor
GPIO[3] Fading Decrement Factor
GPIO[2] Fading Decrement Factor
GPIO[1] Fading Decrement Factor
GPIO[0] Fading Decrement Factor
0x59
GpioIncTime7_6
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Defines the fading increment time.
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GPIO Parameters
Address
Name
Bits Description
3:0 GPIO[6] Fading Increment Time
0x5A
GpioIncTime5_4
7:4 GPIO[5] Fading Increment Time
3:0 GPIO[4] Fading Increment Time
0x5B
GpioIncTime3_2
7:4 GPIO[3] Fading Increment Time
3:0 GPIO[2] Fading Increment Time
0x5C
GpioIncTime1_0
0x0: OFF (default)
0x1: 0.5ms
0x2: 1ms
…
0xF: 7.5ms
7:4 GPIO[1] Fading Increment Time
The total fading in time will be:
GpioIncTime*GpioIncFactor*
(GpioIntensityOn – GpioIntensityOff)
3:0 GPIO[0] Fading Increment Time
0x5D
GpioDecTime7_6
7:4 GPIO[7] Fading Decrement Time
3:0 GPIO[6] Fading Decrement Time
0x5E
GpioDecTime5_4
7:4 GPIO[5] Fading Decrement Time
3:0 GPIO[4] Fading Decrement Time
0x5F
GpioDecTime3_2
7:4 GPIO[3] Fading Decrement Time
3:0 GPIO[2] Fading Decrement Time
0x60
GpioDecTime1_0
7:4 GPIO[1] Fading Decrement Time
3:0 GPIO[0] Fading Decrement Time
0x61
GpioOffDelay7_6
7:4 GPIO[7] OFF Delay
3:0 GPIO[6] OFF Delay
0x62
GpioOffDelay5_4
7:4 GPIO[5] OFF Delay
3:0 GPIO[4] OFF Delay
0x63
GpioOffDelay3_2
7:4 GPIO[3] OFF Delay
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)
Defines the delay after GPO OFF trigger
before fading out starts.
0x0: OFF (default)
0x1: 200ms
0x2: 400ms
…
0xF: 3000ms
3:0 GPIO[2] OFF Delay
0x64
GpioOffDelay1_0
7:4 GPIO[1] OFF Delay
3:0 GPIO[0] OFF Delay
0x65
GpioPullUpDown7_4
7:6 GPIO[7] Pullup/down
5:4 GPIO[6] Pullup/down
3:2 GPIO[5] Pullup/down
Enables pullup/down resistors for GPI pins.
00 : None (default)
01 : Pullup
10 : Pulldown
11 : Reserved
1:0 GPIO[4] Pullup/down
0x66
GpioPullUpDown3_0
7:6 GPIO[3] Pullup/down
5:4 GPIO[2] Pullup/down
3:2 GPIO[1] Pullup/down
1:0 GPIO[0] Pullup/down
0x67
GpioInterrupt7_4
7:6 GPI[7] Interrupt
5:4 GPI[6] Interrupt
3:2 GPI[5] Interrupt
1:0 GPI[4] Interrupt
0x68
GpioInterrupt3_0
7:6 GPI[3] 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
5:4 GPI[2] Interrupt
3:2 GPI[1] Interrupt
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GPIO Parameters
Address
Name
Bits Description
1:0 GPI[0] Interrupt
0x69
GpioDebounce
7:0 GPI[7] Debounce
Enables the GPI debounce (done on 10
consecutive samples at 1ms).
0 : OFF (default)
1 : ON
GPI[6] Debounce
GPI[5] Debounce
GPI[4] Debounce
GPI[3] Debounce
GPI[2] Debounce
GPI[1] Debounce
GPI[0] Debounce
Table 22 GPIO Parameters
Table 23 resumes the applicable SPM and I2C parameters for each GPIO mode.
SPM
I2C
GpioMode
GpioOutPwrUp
GpioAutoligth
GpioPolarity
GpioIntensityOn
GpioIntensityOff
GpioFunction
GpioIncFactor
GpioDecFactor
GpioIncTime
GpioDecTime
GpioOffDelay
GpioPullUpDown
GpioInterrupt
GpioDebounce
IrqSrc[4]
GpiStat
GpoCtrl
GppPinId
GppIntensity
GPI
X
GPP
X
1
X
X
1
X
1
X
X
GPO
X
2
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
3
X
1
X
1
At power up, GppIntensity of each GPP pin is initialized with GpioIntensityOn or GpioIntensityOff depending on GpioOutPwrUp
corresponding bits value.
2
Only if Autolight is OFF, else must be left to 0 (default value)
3
Only if Autolight is OFF, else ignored
Table 23 Applicable SPM/I2C Parameters vs. GPIO Mode
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6 I2C INTERFACE
The I2C implemented on the SX8645 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
processing phase (section 3.3).
Three types of registers are considered:
- status (read). These registers give information about the status of the capacitive buttons, wheel, GPIs, operation
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 SX8645 is powered down.
The SPM can be stored permanently in the NVM memory of the SX8645. The SPM gateway communication over
the I2C at power up is then not required.
The I2C will be able to read and write from a start address and then perform read or writes sequentially, 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
SX8645 then Acknowledges [A] that it is being addressed, and the Master sends an 8 bit Data Byte consisting of
the SX8645 Register Address (RA). The Slave Acknowledges [A] and the master sends the appropriate 8 bit Data
Byte (WD0). Again the Slave Acknowledges [A]. In case the master needs to write more 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 register address is incremented automatically when successive register data (WD1...WDn) is supplied by the
master.
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6.2
DATASHEET
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
SX8645 then Acknowledges [A] that it is being addressed, and the Master responds with an 8 bit Data consisting
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 SX8645 responds with an Acknowledge [A] and the read Data byte (RD0). If the master needs to read more
data it will acknowledge [A] and the SX8645 will send the next read byte (RD1). This 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
DATASHEET
I2C Registers Overview
Address
Name
R/W
Description
0x00
IrqSrc
read
Interrupt Source
0x01
CapStatMsb
read
Wheel/Button Status MSB
0x02
CapStatLsb
read
Button Status LSB
0x03
WhlPosMsb
read
Wheel Position MSB
0x04
WhlPosLsb
read
Wheel 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 I2C Registers Overview
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6.4
DATASHEET
Status Registers
Address
0x00
Name
Bits
Description
7
Reserved
6
NVM burn interrupt flag
5
SPM write interrupt flag
4
GPI interrupt flag
3
Wheel interrupt flag
2
Buttons interrupt flag
1
Compensation interrupt flag
0
Operating Mode interrupt flag
IrqSrc
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 Interrupt 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 set if a Wheel event occurred (touch, release, rotation clockwise, rotation counter clockwise or position
change) . CapStatMsb, WhlPosMsb and WhlPosLsb show the detailed status of the Wheel.
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 actually entering Active or Doze mode either through automatic wakeup or via host request.
CompOpmode shows the current operation mode.
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Address
0x01
0x02
Name
Bits
Description
7
Reserved
6
Wheel Rotation
Clockwise
5
Wheel Rotation
Counter Clockwise
4
Wheel Touched
3
Button 11 Touched
2
Button 10 Touched
1
Button 9 Touched
0
Button 8 Touched
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
0
Button 0 Touched
DATASHEET
Wheel Rotation status
0: No rotation (default)
1: Rotation
The status remains high as long as the wheel is
touched and no opposite rotation has occurred.
CapStatMsb
CapStatLsb
Wheel Touch status
0: Released (default)
1: Touched
Button Touch status
0: Released (default)
1: Touched
Table 26 Wheel, Button status MSB/LSB
Address
Name
Bits
Description
0x03
WhlPosMsb
7:0
Wheel Position[15:8]
0x04
WhlPosLsb
7:0
Wheel Position[7:0]
Shows the current (touched) or last (released)
wheel position[15:0] unsigned (default 0x00)
Table 27 Wheel position MSB/LSB
Address
0x07
Name
GpiStat
Bits
7:0
Description
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
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Address
0x08
Name
DATASHEET
Bits
Description
7:4
reserved
3
NvmValid
2:0
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.
NvmCount
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
Indicates if the current NVM is valid.
0: No – QSM is used
1: Yes – NVM is used
SpmStat
Table 29 I2C SPM status
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6.5
DATASHEET
Control Registers
Address Name
Bits
Description
7:3
Reserved*, write only ‘00000’
2
0x09
Compensation
Indicates/triggers compensation procedure
0: Compensation completed (default)
1: read -> compensation running ; write -> trigger
compensation
Operating Mode
Indicates/programs** operating mode
00: Active mode (default)
01: Doze mode
10: Sleep mode
11: Reserved
CompOpMode
1:0
Table 30 I2C compensation, 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
0x0A
GpoCtrl
Bits
7:0
Description
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
0x0B
Name
Bits
Description
7:3
Reserved, write only ‘00000’
GppPinId
2:0
GPP Pin Identifier
DATASHEET
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
0x0C
Name
GppIntensity
Bits
7:0
Description
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
0xB1
Name
Bits
Description
SoftReset
7:0
Writing 0xDE followed by 0x00 will reset the chip.
Table 34 I2C Soft Reset
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6.6
DATASHEET
SPM Gateway Registers
The SX8645 I2C interface offers two registers for exchanging the SPM data with the host.
• SpmCfg
• SpmBaseAddr
Address
0x0D
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
2:0
000: Reserved
SpmCfg
Table 35 SPM access configuration
Address Name
0x0E
SpmBaseAddr
Bits
Description
7:0
SPM Base Address (modulo 8).
The lowest address is 0x00 (default).
The highest address is 0x78.
Table 36 SPM Base Address
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
0xAC
SpmKeyMsb
Bits
Description
7:0
SPM to NVM burn Key MSB
Unlock requires writing data: 0x62
Table 37 SPM Key MSB
Address
0xAD
Name
Bits
Description
SpmKeyLsb
7:0
SPM to NVM burn Key LSB
Unlock requires writing data: 0x9D
Table 38 SPM Key LSB
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
6.6.1
DATASHEET
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: SPM Write Sequence
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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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
6.6.2
DATASHEET
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: SPM Read Sequence
The complete SPM can be read by repeating 16 times the cycles shown in Figure 55 using base addresses 0x00,
0x08, 0x10, …, 0x70, 0x78.
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
6.7
DATASHEET
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 SX8645 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 SX8645 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.
2. Write the data 0x9D to the I2C register I2CKeyLsb.
3. Write the data 0xA5 to the I2C register I2CSpmBaseAddr.
4. Write the data 0x5A to the I2C register I2CSpmBaseAddr.
Terminate the I2C write by a STOP.
Terminate the I2C write by a STOP.
Terminate the I2C write by a STOP.
Terminate the I2C write by a STOP.
This is illustrated in Figure 57.
1)
S
SA
0
A
0xAC
A
0x62
A
P
2)
S
SA
0
A
0xAD
A
0x9D
A
P
3)
S
SA
0
A
0x0E
A
0xA5
A
P
4)
S
SA
0
A
0x0E
A
0x5A
A
P
S
SA
A
P
: Start condition
: Slave address
: Slave acknowledge
: Stop condition
From master to slave
From slave to master
Figure 57: NVM burn procedure
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
7 APPLICATION INFORMATION
A typical application schematic is shown in Figure 58.
Figure 58 Typical Application
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
8 PACKAGING INFORMATION
8.1
Package Outline Drawing
SX8645 is assembled in a MLPQ-W32 package as shown in Figure 59.
Figure 59 Package Outline Drawing
8.2
Land Pattern
The land pattern of MLPQ-W32 package, 5 mm x 5 mm is shown in Figure 60.
Figure 60 Land Pattern
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SX8645
Ultra Low Power, Capacitive Button and Wheel
Touch Controller (12 sensors) with Enhanced LED Drivers
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
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