IQ Switch
®
ProxSense
®
Series
IQ Switch
®
- ProxSense
®
Series
Minimalist Capacitive Sensor with Compensation for Sensitivity Reducing Objects
Unparalleled Features
Sub 6uA current consumption
Automatic tuning for optimal operation in various environments
The IQS156 ProxSense
®
IC is a fully integrated six channel capacitive contact and proximity
sensor with market leading sensitivity and automatic tuning to the sense electrodes. The IQS156
provides a minimalist implementation requiring as few as 2 external components. The device is
ready for use in a large range of applications while programming options allow customisation for
specialized applications.
IQS156 Datasheet
Main Features
6 Channel input device
I
2
C data output
ATI: Automatic tuning to optimum sensitivity
Supply Voltage 3V to 5.5V
8 Power Modes (6µA min)
Internal voltage regulator and reference capacitor
Large proximity detection range
Automatic drift compensation
Development and Programming tools available (VisualProxSense and USBProg)
Small outline MSOP–10
IQS143 MSOP10
Representations only, not
actual markings
Applications
White goods and appliances
Office equipment, toys, sanitary ware
Flame proof, hazardous environment Human Interface Devices
Proximity detection that enables backlighting activation (Azoteq Patented)
Wake-up from standby applications
Replacement for electromechanical switches
GUI trigger on proximity detection.
Available options
T
A
MSOP-10
IQS156
-40°C to 85°C
IQ Switch
®
ProxSense
®
Series
Functional Overview
1 Introduction
The IQS156 is a six channel projected
capacitive proximity and touch sensor
featuring internal voltage regulator and
reference capacitor (C
s
).
The device has five dedicated input pins for
the connection of the sense electrodes, which
comprises of three receivers, and two
transmitters. Two output pins are used for
serial data communication through the I2C
protocol.
The devices automatically tracks slow varying
environmental changes via various filters,
detect noise and has an automatic Automatic
Tuning Implementation (ATI) to tune the
device for optimal sensitivity.
Table 1.1
Pin
1
4
IQS156 Pin-outs.
I
2
C
GND
Function
Ground
Power
Input
Regulator
Pin
Receiver
Electrode
Receiver
Electrode
Receiver
Electrode
Transmitter
Electrode
Transmitter
Electrode
I
2
C Data
I
2
C Clock
VDDHI
5
VREG
2
CRX0
3
CRX1
9
CRX2
1.1 Applicability
All specifications, except where specifically
mentioned otherwise, provided by this
datasheet are applicable to the following
ranges:
Temperature -40°C to +85°C
Supply voltage (V
DDHI
) 3V to 5.5V
10
CTX0
6
CTX1
7
8
SDA
SCL
1.2 Pin-outs
1. GND
2. CRX0
3. CRX1
4. VDDHI
5. VREG
10. CTX0
9. CRX2
8. SCL
7. SDA
6. CTX1
2 Analogue Functionality
The analogue circuitry measures the
capacitance of the sense electrodes attached
to the Cx pins through a charge transfer
process that is periodically initiated by the
digital circuitry. The measuring process is
referred to a conversion and consists of the
discharging of C
s
and Cx, the charging of Cx
and then a series of charge transfers from Cx
to C
s
until a trip voltage is reached. The
number of charge transfers required to reach
the trip voltage is referred to as the Count
Values (CS).
The capacitance measurement circuitry
makes use of an internal C
s
and voltage
reference (V
REG
).
The analogue
functionality for:
circuitry
further
provides
Figure 1.1
IQS156 Pin-outs.
Copyright © Azoteq (Pty) Ltd 2012.
All Rights Reserved.
IQS156 Datasheet
Revision 1.7
Page 2 of 24
October 2012
IQ Switch
®
ProxSense
®
Series
Power on reset (POR) detection.
Brown out detection (BOD).
Monitoring and automatic execution of the
ATI algorithm.
Signal processing and digital filtering.
Detection of PROX and TOUCH events.
Managing outputs of the device.
Managing serial communications.
3 Digital Functionality
The digital processing
responsible for:
functionality
is
Management of BOD and WDT events.
Initiation of conversions at the selected
rate.
Processing of CS and execution of
algorithms.
Detailed Description
4 Reference Design
Figure 4.1
Reference Design.
Use C3 and C4 for added RF immunity.
Place C1-C4 as close as possible to IC, connected to good GND.
R6 and R7 used as pull up resistors for I
2
C protocol.
Figure 4.2
Output in active low.
proximities at distances that cannot be
equalled by most other products. When the
device is used in environments where noise or
ground effects exist that lower the sensitivity,
a reduced proximity threshold is proposed to
ensure reliable functioning of the sensor. The
high sensitivity allows the device to sense
IQS156 Datasheet
Revision 1.7
Page 3 of 24
October 2012
5 High Sensitivity
Through patented design and advanced signal
processing, the device is able to provide
extremely high sensitivity to detect Proximity.
This enables designs that can detect
Copyright © Azoteq (Pty) Ltd 2012.
All Rights Reserved.
IQ Switch
®
ProxSense
®
Series
accurately through overlays with low dielectric
constants like wood or even air gaps.
8 Charge Transfers
The IQS156 charges in 7 timeslots, with one
internal Cs capacitor. The charge sequence is
6 Adjustable Proximity
shown in Figure 8.1, where CH0 is the Prox
Threshold
channel, and charges before each of the 6
The IQS156 has a default proximity threshold of
input channels.
4. The proximity threshold is selected by the
CH0
CH1 0 CH2 0 CH3 0 CH4 0 CH5 0 CH6 0
PROX
designer (1 to 64) to obtain the desired
sensitivity and noise immunity through the I
2
C
CH1+
CTX0
CTX0
CTX0
CTX1
CTX1
CTX1
CH2+
CRX0
CRX1
CRX2
CRX0
CRX1
CRX2
serial interface. The proximity event is triggered
CH3
based on the selected proximity threshold; the
CS, LTA (Long Term Average) and LTN (Long
Figure 8.1 IQS156 Charge transfer.
Term Noise) filter. The threshold is expressed in
terms of counts; the same as CS.
9 Data Streaming
A proximity event is identified when for at least
4 consecutive samples the following equation
The IQS156 device interfaces to a master
controller via a 2 wire serial interface bus that is
holds:
I
2
C
TM
compatible.
P
TH
=< LTA-CS
The IQS156 can only function as a slave
Where LTA is the Long Term Average
device on the bus. The bus must be controlled
by a master device which generates the serial
7 Adjustable Touch
clock (SCL), controls bus access, and
generates the START and STOP conditions.
Thresholds
The IQS156 has a default touch threshold of
96 (for all six channels). The touch threshold
is selected by the designer to obtain the
desired touch sensitivity and is selectable in
the memory map, individually for each
channel.
The touch event is triggered based on T
TH
, CS
and LTA. A touch event is identified when for
at least 4 consecutive samples the following
equation holds:
T
TH
=< LTA-CS
The serial clock (SCL) and serial data lines
(SDA) are open-drain and therefore must be
pulled high to the operating voltage with a pull-
up resistor (typically 10k).
9.1 Bus Characteristics
The following bus protocol has been defined:
Data transfer may only be initiated when
the bus is not busy
During data transfer the data line must
remain stable whenever the clock line is
HIGH. Changes in the data line while the
clock is HIGH will be interpreted as START
and STOP conditions.
With lower average CS (therefore lower LTA)
values the touch threshold will be lower and
vice versa.
The following conditions have been defined for
the bus (refer to Figure 9.1):
Copyright © Azoteq (Pty) Ltd 2012.
All Rights Reserved.
IQS156 Datasheet
Revision 1.7
Page 4 of 24
October 2012
IQ Switch
®
ProxSense
®
Series
SCL
(A)
(B)
(D)
(D)
(C)
(A)
SDA
Start Condition
Address or
Acknowledge
Valid
Data Allowed
to Change
Stop Condition
Figure 9.1
9.1.2 Bus Idle (A)
Data Transfer Sequence on the Serial Bus.
The IQS156 does not generate any
acknowledge bits while it is not in its
communication window.
The SCL and SDA lines are both HIGH.
9.1.3 START Condition (B)
A start condition is implemented as a HIGH to
LOW transition of SDA, while the SCL is The IQS156 does not have a RDY pin, thus
HIGH. All serial communication must be ACK polling must be used to determine when
the device is ready for communication. The
preceded by a START condition.
device will not acknowledge during a
9.1.4 STOP Condition (C)
conversion cycle.
A stop condition is implemented as a LOW to Once a stop condition is sent by the master
HIGH transition of SDA, while the SCL is the device will perform the next conversion
HIGH. All serial communication must be cycle. ACK polling can be initiated at any time
ended by a STOP condition. NOTE: When a during the conversion cycle to determine if the
STOP condition is sent, the device will exit the device has entered its communication window.
communications window and continue with
To perform ACK polling the master sends a
conversions.
start condition followed by the control byte. If
9.1.5 Data Valid (D)
the device is still busy then no ACK will be
The state of the SDA line represents valid returned. If the device has completed its cycle
data when, after a START condition, the SDA the device will return an ACK, and the master
is stable for the duration of the HIGH period of can proceed with the next read or write
operation (refer to Figure 9.2).
the clock signal.
The data on the line must be changed during
the LOW period of the clock signal. There is
one clock pulse per bit of data.
Each data transfer is initiated with a START
condition and terminated with a STOP
condition.
9.2 Acknowledge Polling
9.1.6 Acknowledge
The slave device must acknowledge (ACK)
after the reception of each byte. The master
device must generate an extra (9th) clock
pulse which is associated with this
acknowledge
bit.
The
device
that
acknowledges, has to pull down the SDA line
during the acknowledge clock pulse. NOTE:
Copyright © Azoteq (Pty) Ltd 2012.
All Rights Reserved.
IQS156 Datasheet
Revision 1.7
Page 5 of 24
October 2012
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