SX9500IULTRT - SEMTECH INTERNATIONAL

WIRELESS & SENSING

SX9500

Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

ENERAL

ESCRIPTION

The SX9500 is a low-cost, very low power 4-channel

capacitive controller that can operate either as a proximity or

button sensor. The SX9500 includes sophisticated on-chip

auto-calibration circuitry to regularly perform sensitivity

adjustments, maintaining peak performance over a wide

variation of temperature, humidity and noise environments,

providing simplified product development and enhanced

performance.

The SX9500 operates directly from an input supply voltage of

2.7 to 5.5V, and includes a separate I2C serial bus supply

input to enable communication with 1.8 – 5.5V hosts. The

I2C serial communication bus reports proximity or touch

detection and is used to facilitate parameter settings

adjustment. Upon a proximity detection, the NIRQ output

asserts, enabling the user to either determine the relative

proximity distance, or simply obtain an indication of

detection.

A dedicated transmit enable (TXEN) pin is available to

synchronize capacitive measurements for applications that

require synchronous detection, enabling very low supply

current and high noise immunity by only measuring proximity

when requested.

RODUCT

EATURES

 2.7 – 5.5V Input Supply Voltage

 Capacitive Sensor Inputs

 Down to 0.08 fF Capacitance Resolution

 Stable Proximity & Touch Sensing With Temperature

 Capacitance Offset Compensation to 30pF

 Active Sensor Guarding

 Automatic Calibration

 Ultra Low Power Consumption:

 Active Mode: 170 uA

 Doze Mode: 18 uA

 Sleep Mode: 2.5 uA

 400KHz I2C Serial Interface

 Four programmable I2C Sub-Addresses

 Input Levels Compatible with 1.8V Host Processors

 Open Drain NIRQ Interrupt pin

 Three (3) Reset Sources: POR, NRST pin, Soft Reset

 -40°C to +85°C Operation

 Compact Size: 3 x 3mm Thin QFN package

 Pb & Halogen Free, RoHS/WEEE compliant

PPLICATIONS

• Notebooks

• Tablets

• Mobile Appliances

RDERING

NFORMATION

Part Number Package

Marking

SX9500IULTRT

QFN-20 ZND8

SX9500EVKA Eval. Kit

3000 Units/reel

YPICAL

PPLICATION CIRCUIT

WIRELESS & SENSING

SX9500

Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

Table of Contents

ENERAL

ESCRIPTION

........................................................................................................................ 1

RODUCT

EATURES

..................................................................................................................... 1

PPLICATIONS

....................................................................................................................................... 1

RDERING

NFORMATION

...................................................................................................................... 1

YPICAL

PPLICATION CIRCUIT

............................................................................................................ 1

1 G

ENERAL

ESCRIPTION

............................................................................................................... 4

1.1

Pin Diagram 4

1.2

Marking Information 4

1.3

Pin Description 5

1.4

Acronyms 5

2 E

LECTRICAL

HARACTERISTICS

................................................................................................. 6

2.1

Absolute Maximum Ratings 6

2.2

Operating Conditions 6

2.3

Thermal Characteristics 6

2.4

Electrical Specifications 7

3 P

ROXIMITY

ENSING

NTERFACE

................................................................................................. 9

3.1

Introduction 9

3.2

Scan Period 9

3.3

Analog Front-End (AFE) 10

3.3.1

Capacitive Sensing Basics 10

3.3.2

AFE Block Diagram 12

3.3.3

Capacitance-to-Voltage Conversion (C-to-V) 12

3.3.4

Shield Control 12

3.3.5

Offset Compensation 12

3.3.6

Analog-to-Digital Conversion (ADC) 13

3.4

Digital Processing 13

3.4.1

Overview 13

3.4.2

PROXRAW Update 15

3.4.3

PROXUSEFUL Update 15

3.4.4

PROXAVG Update 16

3.4.5

PROXDIFF Update 18

3.4.6

PROXSTAT Update 18

3.5

Host Operation 19

3.6

Operational Modes 20

3.6.1

Active 20

3.6.2

Doze 20

3.6.3

Sleep 20

3.6.4

TXEN Pin 20

4 I2C

INTERFACE

........................................................................................................................... 21

4.1

Introduction 21

4.2

I2C Write 21

4.3

I2C Read 21

5 R

ESET

......................................................................................................................................... 23

5.1

Power-up 23

5.2

NRST Pin 23

5.3

Software Reset 24

6 I

NTERRUPT

................................................................................................................................. 25

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SX9500

Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

6.1

Power-up 25

6.2

Assertion and Clearing 25

7 P

INS DESCRIPTION

..................................................................................................................... 26

7.1

and SV

7.2

TXEN 26

7.3

Capacitive Sensing Interface (CS0, CS1, CS2, CS3, CSG) 26

7.4

Host Interface 26

7.4.1

NIRQ 26

7.4.2

SCL, NRST and TXEN 27

7.4.3

SDA 27

8 R

EGISTERS

................................................................................................................................. 28

8.1

Overview 28

8.2

Detailed Description 29

9 A

PPLICATION

NFORMATION

...................................................................................................... 33

9.1

Typical Application Circuit 33

9.2

External Components Recommended Values 33

10 P

ACKAGING

NFORMATION

........................................................................................................ 34

10.1

Outline Drawing 34

10.2

Land Pattern 35

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SX9500

Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

1 G

ENERAL

ESCRIPTION

1.1 Pin Diagram

Figure 1: Pin Diagram

1.2 Marking Information

ZND8

yyww

xxxx

yyww= Date Code

xxxx = Lot Number

Figure 2: Marking Information

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SX9500

Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

1.3 Pin Description

Number

Name Type Description

1 CSG Analog Capacitive Sensor Guard/Shield

2 CS3 Analog Capacitive Sensor 3

3 CS2 Analog Capacitive Sensor 2

4 CS1 Analog Capacitive Sensor 1

5 CS0 Analog Capacitive Sensor 0

6 GND Ground Ground

7 NC Not Used Do Not Connect

8 NC Not Used

Connect

9 NC Not Used

Connect

10 NC Not Used

Connect

11 V

Power Core power supply

12 SV

Power

Host interface power supply

Must be ≤V

at all times (including during power-up and power-down)

13 NIRQ Digital Output Interrupt request, active LOW, requires pull-up resistor to SV

14 SCL Digital Input I2C Clock, requires pull-up resistor to SV

15 SDA Digital I/O I2C Data, requires pull-up resistor to SV

16 TXEN Digital Input Transmit Enable, active HIGH (Tie to SV

if not used).

17 NRST

Digital

Input

External reset, active LOW (Tie to SV

if not used).

18 A1 Digital Input I2C Sub-Address, connect to GND or V

19 A0 Digital Input I2C Sub-Address, connect to GND or V

20 GND Ground Ground

DAP GND Ground Exposed Pad. Connect to Ground

Table 1: Pin Description

1.4 Acronyms

DAP Die Attach Paddle

RF Radio Frequency

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SX9500

Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

2 E

LECTRICAL

HARACTERISTICS

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

“Operating Conditions”, is not implied. Exposure to Absolute Maximum Rating conditions for extended periods

may affect device reliability and proper functionality.

Parameter Symbol Min Max Unit

Supply Voltage V

-0.5 6.0

V SV

-0.5 6.0

Input Voltage (non-supply pins) V

-0.5 V

+0.3

Input Current (non-supply pins) I

-10 10 mA

Operating Junction Temperature T

JCT

-40 125

°C Reflow Temperature T

- 260

Storage Temperature T

STOR

-50 150

ESD HBM (Human Body model, to JESD22-A114) ESD

HBM

8 - kV

Table 2: Absolute Maximum Ratings

2.2 Operating Conditions

Parameter Symbol Min Max Unit

Supply Voltage V

2.7 5.5 V

1.65 V

Ambient Temperature T

-40 85 °C

Table 3: Operating Conditions

Note: During power-up or power-down, SVDD must be less than or equal to VDD

2.3 Thermal Characteristics

Parameter

Symbol

Typical

Unit

Thermal Resistance – Junction to Air

(Static Airflow)

°C/W

Table 4: Thermal Characteristics

Note:

is calculated from a package in still air, mounted to 3" x 4.5", 4-layer FR4 PCB with thermal vias under

exposed pad per JESD51 standards.

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Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

2.4 Electrical Specifications

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

Typical values are given for T

= +25°C, VDD=SVDD=3.3V unless otherwise specified.

Parameter Symbol Conditions Min Typ Max Unit

Current Consumption

Sleep

(no sensor enabled) I

SLEEP

Power down, all analog circuits shut

down. (I2C listening)

- 2.5 -

Doze

(all sensors enabled) I

DOZE

SCAN

PERIO

D =

DOZEPERIOD = 2xSCANPERIOD

FREQ = 167kHz

RESOLUTION = Medium

VDD = 5V

- 18 -

Active

(all sensors enabled) I

ACTIVE

SCANPERIOD

= 30m

FREQ = 167kHz

RESOLUTION = Medium

VDD = 5V

- 170 -

Outputs: SDA, NIRQ

Output Cur

rent at Output Low

Voltage I

VOL = 0.4V 6 - - mA

Maximum Output LOW Voltage V

(Max) SV

> 2V - - 0.4 V

≤ 2V - - 0.2 x SV

Inputs: SCL, SDA, TXEN

Input logic high V

0.8 x SV

- SV

+ 0.3 V

Input logic low V

-0.3 - 0.25 x SVDD

Input leakage current I

CMOS input -1 - 1 uA

Hysteresis

HYS

> 2V -

0.05x

≤ 2V -

0.1x

TXEN Delay TXEN

ACTDLY

Delay

between TXEN rising

edge and SX9500 starting

measurements - 100 - µs

Input

A0, A1

Input logic high V

0.7 x V

- V

+ 0.3 V

Input logic low V

-0.3 - 0.3 x VDD

Input: NRST

Input logic high V

> 2V 0.7 x SV

- SV

+ 0.3

≤ 2V 0.75 x SV

Input logic low V

> 2V - - 0.6

≤ 2V - - 0.3 x SV

NRST minimum pulse width

RESETPW

µs

Start-up

Power-up time T

POR

- 1 - ms

Table 5: Electrical Specifications

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Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

Parameter Symbol Conditions Min Typ Max Unit

I2C Timing Specifications (Cf.

Figure 3

and

Figure 4

below)

SCL clock frequency

SCL

400

L low period

LOW

1.3

SCL high period

HIGH

0.6

Data setup time

SU;DAT

Data hold time

HD;DAT

Repeated start setup time

SU;STA

0.6

Start condition hold time

HD;STA

0.6

Stop condition setup time

SU;STO

0.6

Bus free time between stop and start

BUF

1.3

Input glitch suppression

Note 1

Note 1: Minimum glitch amplitude is 0.7V

at High level and Maximum 0.3V

at Low level.

Table 6: I2C Timing Specifications

Figure 3

: I2C Start and Stop Timing

Figure 4: I2C Data Timing

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SX9500

Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

3 P

ROXIMITY

ENSING

NTERFACE

3.1 Introduction

The purpose of the proximity sensing interface is to detect when a conductive object (usually a body part i.e.

finger, palm, face, etc) is in the proximity of the system. Note that proximity sensing can be done thru the air or

thru a solid (typically plastic) overlay (also called “touch” sensing).

The chip’s proximity sensing interface is based on capacitive sensing technology. An overview is given in figure

below.

Shield

Sensor Analog

Front-End

(AFE)

Digital

Processing

SX9500

PROXSTAT

0 1 0

Finger, palm,

face, lap, etc

CSx

CSG

Figure 5: Proximity Sensing Interface Overview

 The sensor can be a simple copper area on a PCB or FPC for example. Its capacitance (to ground) will

vary when a conductive object is moving in its proximity.

 The optional shield can be also be a simple copper area on a PCB or FPC below/under/around the

sensor. It is used to protect the sensor against potential surrounding noise sources and improve its

global performance. It also brings directivity to the sensing, for example sensing objects approaching

from top only.

 The analog front-end (AFE) performs the raw sensor’s capacitance measurement and converts it into a

digital value. It also controls the shield. See §3.3 for more details.

 The digital processing block computes the raw capacitance measurement from the AFE and extracts a

binary information PROXSTAT corresponding to the proximity status, i.e. object is “Far” or “Close”. It also

triggers AFE operations (compensation, etc). See §3.4 for more details.

3.2 Scan Period

To save power and since the proximity event is slow by nature, the chip will be waken-up regularly at every

programmed scan period (SCANPERIOD) to first sense sequentially each of the enabled CSx pins and then

process new proximity samples/info. The chip will be in idle mode most of the time. This is illustrated in figure

below

Figure 6: Proximity Sensing Sequencing

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Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

The sensing and processing phase’s durations vary with the number of sensors enabled, the sampling

frequency, and the resolution programmed. During the Idle phase, the SX9500‘s analog circuits are turned off.

Upon expiry of the idle timer, a new scan period cycle begins.

The scan period determines the minimum reaction time (actual/final reaction time also depends on debounce and

filtering settings) and can be programmed from 30ms to 400ms.

3.3 Analog Front-End (AFE)

3.3.1 Capacitive Sensing Basics

Capacitive sensing is the art of measuring a small variation of capacitance in a noisy environment. As mentioned

above, the chip’s proximity sensing interface is based on capacitive sensing technology. In order to illustrate

some of the user choices and compromises required when using this technology it is useful to understand its

basic principles.

To illustrate the principle of capacitive sensing we will use the simplest implementation where the sensor is a

copper plate on a PCB.

The figure below shows a cross-section and top view of a typical capacitive sensing implementation. The sensor

connected to the chip is a simple copper area on top layer of the PCB. It is usually surrounded (shielded) by

ground for noise immunity (shield function) but also indirectly couples via the grounds areas of the rest of the

system (PCB ground traces/planes, housing, etc). For obvious reasons (design, isolation, robustness …) the

sensor is stacked behind an overlay which is usually integrated in the housing of the complete system.

PCB dielectric

Ground

Cut view

Top view

PCB copper

Sensor

Overlay

Figure 7: Typical Capacitive Sensing Implementation

When the conductive object to be detected (finger/palm/face, etc) is not present, the sensor only sees an

inherent capacitance value C

Env

created by its electrical field’s interaction with the environment, in particular

with ground areas.

When the conductive object (finger/palm/face, etc) approaches, the electrical field around the sensor will be

modified and the total capacitance seen by the sensor increased by the user capacitance C

User

. This

phenomenon is illustrated in the figure below.

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Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

Figure 8: Proximity Effect on Electrical Field and Sensor Capacitance

The challenge of capacitive sensing is to detect this relatively small variation of C

Sensor

User

usually contributes

for a few percent only) and differentiate it from environmental noise (C

Env

also slowly varies together with the

environment characteristics like temperature, etc). For this purpose, the chip integrates an auto offset

compensation mechanism which dynamically monitors and removes the C

Env

component to extract and process

User

only. See §3.3.5 for more details.

In first order, C

User

can be estimated by the formula below:

is the common area between the two electrodes hence the common area between the user’s finger/palm/face

and the sensor.

is the distance between the two electrodes hence the proximity distance between the user and the system.

is the free space permittivity and is equal to 8.85 10e-12 F/m (constant)

is the dielectric relative permittivity.

Typical permittivity of some common materials is given in the table below.

Material Typical

Glass

FR4

Acrylic Glass 3

Wood 2

Air

Table 7: Typical Permittivity of Some Common Materials

From the discussions above we can conclude that the most robust and efficient design will be the one that

minimizes C

Env

value and variations while improving C

User

Aεε

User

⋅

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Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

3.3.2 AFE Block Diagram

Figure 9: Analog Front-End Block Diagram

3.3.3 Capacitance-to-Voltage Conversion (C-to-V)

The sensitivity of the interface is defined by RANGE and GAIN parameters.

PROXFREQ defines the operating frequency of the interface and should be set as high as possible for power

consumption reasons.

3.3.4 Shield Control

SHIELDEN allows enabling or disabling the shield function.

3.3.5 Offset Compensation

Offset compensation consists in performing a one-time measurement of C

Env

and subtracting it to the total

capacitance C

Sensor

in order to feed the ADC with the closest contribution of C

User

only.

Figure 10: Offset Compensation Block Diagram

The ADC input C

User

is the total capacitance C

Sensor

to which C

Env

is subtracted.

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Ultra Low Power, Four Channels

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There are five possible compensation sources which are illustrated in the figure below. When set to 1 by any of

these sources, COMPSTAT will only be reset once the compensation is completed.

Figure 11: Compensation Request Sources

 Reset: a compensation for all sensors is automatically requested when a reset is performed (power-up,

NRST pin, RegReset)

 COMPDONEIRQ (I2C): a compensation for all sensors can be manually requested anytime by the host

through I2C interface by writing a 1 into COMPDONEIRQ.

 AVGTHRESH: a compensation for all sensors or only the affected one (depending on COMPMETHOD)

can be automatically requested if it is detected that C

Env

has drifted beyond a predefined range

programmed by the host.

 COMPPRD: a compensation can be automatically requested at a predefined rate programmed by the

host.

 STUCK: a compensation can be automatically requested if it is detected that the proximity “Close” state

lasts longer than a predefined duration programmed by the host.

Please note that the compensation request flag can be set anytime but the compensation itself is always done at

the beginning of a scan period to keep all parameters coherent.

Also, when compensation occurs, all PROXSTAT flags turn OFF (ie no proximity detected) independently from

the user’s potential actual presence.

3.3.6 Analog-to-Digital Conversion (ADC)

An ADC is used to convert the analog capacitance information into a digital word PROXRAW.

3.4 Digital Processing

3.4.1 Overview

The main purpose of the digital processing block is to convert the raw capacitance information coming from the

AFE (PROXRAW) into a robust and reliable digital flag (PROXSTAT) indicating if something is close to the

proximity sensor.

The offset compensation performed in the AFE is a one-time measurement. However, the environment

capacitance C

Env

may vary with time (temperature, nearby objects, etc). Hence, in order to get the best

estimation of C

User

(PROXDIFF) it is needed to dynamically track and subtract C

Env

variations. This is performed

by filtering PROXUSEFUL to extract its slow variations (PROXAVG).

PROXDIFF is then compared to user programmable threshold (PROXTHRESH) to extract PROXSTAT flag.

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Ultra Low Power, Four Channels

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Figure 12: Digital Processing Block Diagram

Digital processing sequencing is illustrated in figure below. At every scan period wake-up, the block updates

sequentially PROXRAW, PROXUSEFUL, PROXAVG, PROXDIFF and PROXSTAT before going back to Idle

mode.

Figure 13: Digital Processing Sequencing

Digital processing block also updates COMPSTAT (set when compensation is currently pending execution or

completion)

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Ultra Low Power, Four Channels

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3.4.2 PROXRAW Update

PROXRAW update consists mainly in starting the AFE and waiting for the new PROXRAW values (one for each

CSx/sensor pin) to be ready. If compensation was pending it is performed first.

Figure 14: ProxRaw Update

Note that PROXRAW is not available in the “Sensor Data Readback” section of the registers. If needed it can be

observed by setting RAWFILT=00 and reading PROXUSEFUL.

3.4.3 PROXUSEFUL Update

PROXUSEFUL update consists in filtering PROXRAW upfront to remove its potential high frequencies

components(system noise, interferer, etc) and extract only user activity (few Hz max) and slow environment

changes.

Figure 15: PROXUSEFUL Update

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Ultra Low Power, Four Channels

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3.4.4 PROXAVG Update

PROXAVG update consists in averaging PROXUSEFUL to ignore its “fast” variations (i.e. user finger/palm/hand)

and extract only the very slow variations of environment capacitance C

Env

One can program a debounced threshold (AVGTHRESH/AVGDEB) to define a range within which PROXAVG

can vary without triggering compensation (i.e. small acceptable environment drift).

Large positive values of PROXUSEFUL are considered as normal (user finger/hand/head) but large negative

values are considered abnormal and should be compensated quickly. For this purpose, the averaging filter

coefficient can be set independently for positive and negative variations via AVGPOSFILT and AVGNEGFILT.

Typically we have AVGPOSFILT > AVGNEGFILT to filter out (abnormal) negative events faster.

To prevent PROXAVG to be “corrupted” by user activity (should only reflect environmental changes) it is frozen

when proximity is detected.

Figure 16: ProxAvg vs Proximity Event

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Ultra Low Power, Four Channels

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Figure 17: ProxAvg Update

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3.4.5 PROXDIFF Update

PROXDIFF update consists in the complementary operation i.e. subtracting PROXAVG to PROXUSEFUL to

ignore slow capacitances variations (C

Env

) and extract only the user related variations i.e. C

User

Figure 18: ProxDiff Update

Note that only the 12 upper bits of [PROXUSEFUL – PROXAVG] are kept for PROXDIFF.

3.4.6 PROXSTAT Update

PROXSTAT update consists in taking PROXDIFF information (C

User

), comparing it with a user programmable

threshold PROXTHRESH and finally updating PROXSTAT accordingly. When PROXSTAT=1, PROXAVG is

frozen to prevent the user proximity signal averaging and hence absorbed into C

Env

Figure 19: PROXSTAT Update

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3.5 Host Operation

An interrupt can be triggered when the user is detected to be close (in range), detected to be far (out of range),

or both (CLOSEIRQEN, FARIRQEN).

Figure 20: Proximity Sensing Host Operation (RegIrqMsk[6:3] = 1100)

An interrupt can also be triggered at the end of each proximity sensing operation, indicating to the host when the

proximity sensing block is running (CONVDONEIRQEN). This may be used by the host to synchronize noisy

system operations or to read sensor data (PROXUSEFUL, PROXAVG, PROXDIFF) synchronously for

monitoring purposes.

Figure 21: Proximity Sensing Host Operation (RegIrqMsk[6:3] = 0001)

In both cases above, an interrupt can also be triggered at the end of compensation (COMPDONEIRQEN).

Idle

NIRQ

I2C Read

Proxi

mity Sensing (Analog + Digital)

PROXSTAT

SCANPERIOD

tick

User in

User out of range

Idle

NIRQ

I2C Read

RegIrqSrc

Proximity Sensing (Analog + Digital)

PROXSTAT

SCANPERIOD

tick

User in

User out of range

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3.6 Operational Modes

3.6.1 Active

Active mode has the shortest scan periods, typically 30ms. In this mode, all enabled sensors are scanned and

information data is processed within this interval. The Active scan period is user configurable (SCANPERIOD)

and can be extended up to 400ms.

3.6.2 Doze

In some applications, the reaction/sensing time needs to be fast when the user is present (proximity detected),

but can be slow when not detection has been done for some time.

The Doze mode, when enabled (DOZEEN), allows the chip to automatically switch between a fast scan period

(SCANPERIOD) during proximity detection and a slow scan period (DOZEPERIOD) when no proximity is being

detected (up to 6.4s). This allows reaching low average power consumption values at the expense obviously of

longer reaction times.

As soon as proximity is detected on any sensor, the chip will automatically switch to Active mode while when it

has not detected an object for DOZEPERIOD, it will automatically switch to Doze mode.

3.6.3 Sleep

Sleep mode can be entered by disabling all sensors (SENSOREN=0000). It places the SX9500 in its lowest

power mode, with sensor scanning completely disabled and idle period set to continuous. In this mode, only the

I2C serial bus is active. Enabling any sensor will make the chip leave Sleep mode (for Doze if enabled, else

Active mode)

3.6.4 TXEN Pin

The TXEN input enables proximity sensing when HIGH, likewise when the TXEN input is LOW, the SX9500 is in

Sleep mode. Specifically, on the rising edge of TXEN the SX9500 will begin measuring the sensors normally at

the programmed rate (SCANPERIOD, DOZEPERIOD) as long as TXEN remains HIGH. When TXEN goes LOW

the current measurement sequence will complete and then measurement will cease until the next rising edge of

TXEN.

This feature can be used to synchronize proximity sensing with noisy and/or RF activity for example.

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4 I2C

INTERFACE

4.1 Introduction

The I2C implemented on the SX9500 and used by the host to interact with it is compliant with:

- Standard (100kb/s) and fast mode (400kb/s)

- Slave mode

- 7-bit address (default is 0x28 assuming A1=A0=0)

The SX9500 has two I/O pins (A0 and A1) that provides four possible, user selectable I2C addresses:

Table 8: I2C Sub-Address Selection

The host can use the I2C to read and write data at any time, and these changes are effective immediately.

Therefore the user should ideally disable the sensor before changing settings, or discard the results while

changing.

4.2 I2C Write

The format of the I2C write is given in Figure 12. After the start condition [S], the slave address (SA) is sent,

followed by an eighth bit (‘0’) indicating a Write. The SX9500 then Acknowledges [A] that it is being addressed,

and the Master sends an 8 bit Data Byte consisting of the SX9500 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 22: I2C Write

The register address is incremented automatically when successive register data (WD1...WDn) is supplied by the

master.

4.3 I2C Read

The format of the I2C read is given in Figure 13. After the start condition [S], the slave address (SA) is sent,

followed by an eighth bit (‘0’) indicating a Write. The SX9500 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 SX9500 responds with an Acknowledge [A] and the read

A1 A0 Address

0 0 0x28

0 1 0x29

1 0 0x2A

1 1 0x2B

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Data byte (RD0). If the master needs to read more data it will acknowledge [A] and the SX9500 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 23: I2C Read

The register address is incremented automatically when successive register data (RD1...RDn) is retrieved by the

master.

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5 R

ESET

5.1 Power-up

During a power-up condition, the NIRQ output is HIGH until V

has met the minimum input voltage requirements

and a T

POR

time has expired upon which, NIRQ asserts to a LOW condition indicating the SX9500 is initialized.

The host must perform an I2C read of RegIrqSrc to clear this NIRQ status. The SX9500 is then ready for normal

I2C communication and is operational.

Figure 24: Power-up vs. NIRQ

5.2 NRST Pin

When the host asserts NRST LOW (for min. T

RESETPW

) and then HIGH, the SX9500 will reset its internal registers

and will become active after T

POR

. When not used, this pin must be pulled high to SV

Figure 25: Hardware Reset

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5.3 Software Reset

The host can also perform a reset anytime by writing 0xDE into RegReset. The NIRQ output will be asserted

LOW and the Host is required to perform an I2C read to clear this NIRQ status.

NIRQ

SX9500

Ready

High

HOST issues a soft Reset

HOST clears

the Interrupt

Low

Figure 26: Software Reset

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6 I

NTERRUPT

Except RESETIRQ, all interrupt sources are disabled by default upon power-up and resets, and thus must be

enabled by the host. Any or all of the following interrupts can be enabled by writing a “1” into the appropriate

locations within the RegIrqMsk register:

• Close (proximity detected)

• Far (proximity un-detected)

• Compensation completed

• Conversion completed

The interrupt status can be read from RegIrqSrc for each of these interrupt sources.

6.1 Power-up

During initial power-up, the NIRQ output is HIGH. Once the SX9500 internal power-up sequence has completed,

NIRQ is asserted LOW, signaling that the SX9500 is ready. The host must perform a read to RegIrqSrc to

acknowledge and the SX9500 will clear the interrupt and release the NIRQ line.

6.2 Assertion and Clearing

The NIRQ can be asserted in either the Active or Doze mode during a scan period. The NIRQ will be

automatically cleared after the host performs a read of RegIrqSrc (which content will be cleared as well).

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Ultra Low Power, Four Channels

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7 P

INS DESCRIPTION

7.1 V

and SV

These are the device supply voltages. V

is the supply voltage for the internal core. SV

is the supply

voltage for the host interface. NOTE: SV

MUST be equal or lower than V

at all times.

7.2 TXEN

This signal can be used in many applications if a conversion trigger/enable is needed. This input pin

synchronizes the Capacitance Sensing inputs in systems that need to (for example) transmit RF signals. When

this signal is active, SX9500 performs capacitive measurements. If this input becomes inactive during the middle

of a measurement, the SX9500 will complete all remaining measurements and will enter sleep mode until TXEN

goes active again.

7.3 Capacitive Sensing Interface (CS0, CS1, CS2, CS3, CSG)

The Capacitance Sensing input pins CS0, CS1, CS2 and CS3 are connected directly to the Capacitance Sensing

Interface circuitry which converts the sensed capacitance into digital values. The Capacitive Sensor Guard

(CSG) output provides a guard reference to minimize the parasitic sensor pin capacitances to ground.

Capacitance sensor pins which are not used must not be connected. Additionally, CSx pins must be connected

directly to the capacitive sensors using a minimum length circuit trace to minimize external “noise” pick-up.

The capacitance sensor and capacitive sensor guard pins are protected from ESD events to VDD and GROUND.

7.4 Host Interface

The Host Interface consists of: NIRQ, NRST, SCL, SDA, and TXEN. These signals are discussed below.

7.4.1 NIRQ

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

protected from ESD events to VDD and GROUND.

Figure 27: NIRQ Output Simplified Diagram

SVDD

INT

NIRQ

SX9500

INT

NIRQ to Host

VDD

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7.4.2 SCL, NRST and TXEN

The SCL, NRST and TXEN pins are high impedance input pins that require an external pull-up resistor (1..10

kOhm). NRST and TXEN can be connected without the requirement for a pull-up resistor if driven from a push-

pull host output. These pins are protected from ESD events to VDD and GROUND.

Figure 28: SCL/TXEN/NRST

7.4.3 SDA

SDA is an I/O pin that requires an external pull-up resistor (1…10 kOhm). The SDA I/O pin is protected to VDD

and GROUND.

Figure 29: SDA Simplified Diagram

SVDD

SDA

SDA_OUT

To/From Host

SDA_IN

VDD

SVDD

CL/TXEN/NRST

From

Host

SCL_IN/TXEN

_IN/NRST_IN

VDD

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8 R

EGISTERS

8.1 Overview

The SX9500 allows the user full parameter customization for sensor sensitivity, hysteresis, detection thresholds,

etc. Custom parameters are controlled thru the volatile registers below and must be uploaded by the host thru

I2C after power-up or after a reset.

Address

Name

Default

Description

0x00

RegIrqSrc

0x80

Interrupt & Status 0x01 RegStat 0x0F

0x03 RegIrqMsk 0x00

0x06 RegProxCtrl0 0x0F

Proximity Sensing Control

0x07

RegProx

Ctrl1

0x40

0x08

RegProx

Ctrl2

0x08

0x09 RegProxCtrl3 0x40

0x0A RegProxCtrl4 0x00

0x0B RegProxCtrl5 0x00

0x0C RegProxCtrl6 0x00

0x0D

RegProx

Ctrl7

0x00

0x0E

RegProx

Ctrl8

0x00

RegSensorSel

0x00

Sensor Data Readback

0x21 RegUseMsb 0x00

0x22 RegUseLsb 0x00

0x23 RegAvgMsb 0x00

0x2

Reg

AvgL

0x00

0x2

RegDiff

0x00

0x2

RegDiff

0x00

0x27 RegOffsetMsb 0x00

0x28 RegOffsetLsb 0x00

0x7F RegReset 0x00 Software Reset

Table 9: Registers Overview

NOTES:

1) Addresses not listed above are reserved and should not be written.

2) Reserved bits should be left to their default value unless otherwise specified.

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Ultra Low Power, Four Channels

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8.2 Detailed Description

Addr.

Name

R/W

Bits

Variable

Default

Function

Interrupt

Status

0x00

RegIrqSrc

RESETIRQ

Reset interrupt source status. (i.e.

reset occurred)

6 CLOSEIRQ 0 Close interrupt source status. (i.e.

PROXSTATx rising edge)

FARIRQ

Far interrupt source status. (i.e.

PROXSTATx falling edge)

R/W

4 COMPDONEIRQ 0 Compensation interrupt source

status. (i.e. compensation occurred)

When set to 1, triggers

compensation

R 3 CONVDONEIRQ 0 Conversion interrupt source status.

(i.e. new set of sensor data

available)

2:1 Reserved 00

0 TXENSTAT 0 Indicates current TXEN pin status.

0x01 RegStat R 7 PROXSTAT3 0 Indicates if proximity is being

detected for CS3

(i.e. sensor’s PROXDIFF value is

above detection threshold)

PROX

STAT

Indicates if proximity is being

detected for CS2

(i.e. sensor’s PROXDIFF value is

above detection threshold)

PROXSTAT

Indicates if proximity is being

detected for CS1

(i.e. sensor’s PROXDIFF value is

above detection threshold)

4 PROXSTAT0 0 Indicates if proximity is being

detected for CS0

(i.e. sensor’s PROXDIFF value is

above detection threshold)

3:0 COMPSTAT 1111 Indicates which capacitive sensor(s)

has a compensation pending.

[3:0] = [CS3, CS2, CS1, CS0]

0x03 RegIrqMsk R 7 Reserved 0

R/W

6 CLOSEIRQEN 0 Enables the close interrupt.

5 FARIRQEN 0 Enables the far interrupt.

4 COMPDONEIRQEN 0 Enables the compensation interrupt.

3 CONVDONEIRQEN 0 Enables the conversion interrupt.

R 2:0 Reserved 000

Proximity

Sensing C

ontrol

0x06

Reg

Prox

Ctrl0

R/W

Reserved

6:4

SCAN

PERIOD

000

Defines

the

Active

scan

period :

000: 30 ms (Typ.)

001: 60 ms

010: 90 ms

011: 120 ms

100: 150 ms

101: 200 ms

110: 300 ms

111: 400 ms

Low values will allow fast reaction

time while high values will provide

low power consumption.

3:0

SENSOREN

1111

Enable

s sensor pins.

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Ultra Low Power, Four Channels

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[3:0] = [CS3, CS2, CS1, CS0]

0x07 RegProxCtrl1 R/W

7:6 SHIELDEN 01 Enables shield function on CSG pin:

00: Off, high impedance.

01: On (Typ.)

1x: Reserved

R/W

5:2

Reserved

0000

R/W

1:0

RANGE

Defines the input capacitance range:

00: Large (typ. +/-7.3pF FS)

01: Medium Large (typ. +/-3.7pF FS)

10: Medium Small (typ. +/-3pF FS)

11: Small (typ. +/-2.5pF FS)

This parameter can be seen as an

analog gain (small range = high

gain)

Full scale (FS) values assume no

digital gain.

0x08

RegProx

Ctrl2

R/W

Reserved

6:5 GAIN 00 Defines the digital gain factor:

00: Off (x1)

01: x2

10: x4

11: x8 (Typ.)

This is a pure digital gain (value

shift) applied at the ADC output.

4:3

FREQ

Defines

the

sampling

frequency

00: 83 kHz

01: 125 kHz

10: 167 kHz (Typ.)

11: Reserved

2:0

RESOLUTION

000

Defines

the

capacitance

measurement resolution/precision:

000: Coarsest

….

100: Medium

….

111: Finest (Typ.)

0x09 RegProxCtrl3 R/W

7 Reserved 0

6 DOZEEN 1 Enables Doze mode.

5:4 DOZEPERIOD 00 When DOZEN=1, defines the Doze

scan period:

00: 2x SCAN

PERIOD

01: 4x SCANPERIOD

10: 8x SCANPERIOD

11: 16x SCANPERIOD

3:2 Reserved 00

1:0 RAWFILT 00 Defines PROXRAW filter strength :

00: Off - No filtering

01: Low (Typ.)

10: Medium

11: High - Max filtering

0x0A RegProxCtrl4 R/W

7:0 AVGTHRESH

0x00 Defines the positive and negative

average thresholds which will trigger

compensation:

Thresholds = +/- 128x AVGTHRESH

Typically set between +/-16384 and

+/-24576 (i.e. ½ to ¾ of the system

dynamic range).

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Ultra Low Power, Four Channels

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Should not be set below 0x40.

0x0B RegProxCtrl5 R/W

7:6 AVGDEB

00 Defines the average debouncer

applied to AVGTHRESH:

00: Off

01: 2 samples

10: 4 samples

11: 8 samples

5:3 AVGNEGFILT 000 Defines the average negative filter

strength:

000: Off - No filtering

001: Lowest (Typ.)

….

111: Highest - Max filtering

2:0 AVGPOSFILT 000 Defines the average positive filter

strength:

000: Off - No filtering

001: Lowest

….

111: Highest - Max filtering (Typ.)

0x0C RegProxCtrl6 R/W

7:5 Reserved 000

4:0 PROXTHRESH 00000 Defines the proximity detection

threshold (for all sensors).

00000: 0

00001: 20

00010: 40

00011: 60

00100: 80

00101: 100

00110: 120

00111: 140

01000: 160

01001: 180

01010: 200

01011: 220

01100: 240

01101: 260

01110: 280

01111: 300

10000: 350

10001: 400

10010: 450

10011: 500

10100: 600

10101: 700

10110: 800

10111: 900

11000: 1000

11001: 1100

11010: 1200

11011: 1300

11100: 1400

11101: 1500

11110: 1600

11111: 1700

Low values allow good

sensitivity/distance while higher

values allow better noise immunity.

0x0D

Reg

Prox

Ctrl7

R/W

AVGCOMPDIS

Disables the automatic

compensation triggered by

AVGTHRESH.

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6 COMPMETHOD 0 Defines the compensation method:

0: Compensate each CSx pin

independently (Typ.)

1: Compensate all CSx pins

together.

5:4

HYST

fines the proximity de

tection

hysteresis applied to

PROXTHRESH:

00: 32

01: 64

10: 128

11: 256

3:2 CLOSEDEB 00 Defines the Close debouncer applied

to PROXTHRESH:

00: Off

01: 2 samples

10: 4 samples

11: 8 samples

1:0 FARDEB 00 Defines the Far debouncer applied to

PROXTHRESH:

00: Off

01: 2 samples

10: 4 samples

11: 8 samples

0x0E RegProxCtrl8 R/W

7:4 STUCK 0000 Defines the proximity “stuck” timeout:

0000 : Off (Typ.)

00XX: STUCK x 64 samples

01XX: STUCK x 128 samples

1XXX: STUCK x 256 samples

3:0 COMPPRD 0000 Defines the periodic compensation

interval:

0000: Off (Typ.)

Else: COMPPRD x 128 samples

Sensor

Data R

eadback

0x20 RegSensorSel

R 7:2 Reserved 000000

RW 1:0 SENSORSEL 00 Defines which sensor’s data will be

available in registers RegUseMsb to

RegOffsetLsb (addr. 0x21 to 0x28):

00: CS0

01: CS1

10: CS2

11: CS3

0x21 RegUseMsb R 7:0 PROXUSEFUL 0x00 Useful current value.

Signed, 2's complement format.

0x22 RegUseLsb R 7:0 0x00

0x23 RegAvgMsb R 7:0 PROXAVG 0x00 Average current value.

Signed, 2's complement format.

0x24 RegAvgLsb R 7:0 0x00

0x25 RegDiffMsb R 7:0 PROXDIFF 0x00 Diff current value.

Signed, 2's complement format.

0x26 RegDiffLsb R 7:0 0x00

0x27 RegOffsetMsb

R/W

7:0 PROXOFFSET 0x00 Compensation offset current value.

Unsigned.

To force a value, MSB and LSB

registers must be written in

sequence and change is effective

after LSB.

0x28 RegOffsetLsb R/W

7:0 0x00

Software

Reset

0x7F RegReset W 7:0 SOFTRESET 0x00 Writing 0xDE resets the chip.

Table 10: Registers Detailed Description

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SX9500

Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

9 A

PPLICATION

NFORMATION

9.1 Typical Application Circuit

Figure 30: Typical Application Circuit

9.2 External Components Recommended Values

Symbol Description Note Min Typ. Max Unit

CVDD Core supply decoupling capacitor - 100 - nF

VDD

Host interface

supply decoupling capacitor

100

RPULL

Host interface pull

ups

50%

kΩ

Table 11: External Components Recommended Values

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SX9500

Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

10 P

ACKAGING

NFORMATION

10.1 Outline Drawing

Figure 31: Outline Drawing

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SX9500

Ultra Low Power, Four Channels

Capacitive Proximity/Button Solution

10.2 Land Pattern

Figure 32: Land Pattern

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Ultra Low Power, Four Channels

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Contact Information

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

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

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Notice: All referenced brands, product names, service names and trademarks are the property of their

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Semtech Corporation

Wireless and Sensing Products Division

200 Flynn Road, Camarillo, CA 93012

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