ATMEL AT42QT2100-AU

Atmel AT42QT2100
QTouch Touch Sensor IC
DATASHEET
Features
• Number of QTouch® Keys:
– 0 to 7, one slider or one wheel
• Technology:
•
•
•
•
•
•
•
•
•
•
•
•
•
– Patented spread-spectrum charge-transfer
Key Outline Sizes:
– 5 mm x 5 mm or larger (panel thickness dependent); widely different sizes
and shapes possible
Key Spacing:
– 6 mm or wider, center to center (panel thickness, human factors
dependent)
Key Design:
– Single solid or ring shaped electrodes; wide variety of possible layouts
Wheel Size:
– Typically 30 – 50 mm diameter, resistively interpolated wheel up to 80 mm
diameter, typical width 12 mm
Slider Size:
– Typically 50 – 100 mm length, typical width 12 mm
Slider/Wheel Electrode Design:
– Choice of spatially interpolated (resistorless) or resistively interpolated
design
– Slider can be an arc or other irregular shape
Layers Required:
– One layer substrate; electrodes and components can be on same side
Substrates:
– FR-4, low cost CEM-1 or FR-2 PCB materials; polyamide FPCB; PET films,
glass
Electrode Materials:
– Copper, silver, carbon, ITO, virtually anything electrically conductive
Panel materials:
– Plastic, glass, composites, painted surfaces (nonconductive paints)
Adjacent Metal:
– Compatible with grounded metal immediately next to keys
Panel Thickness:
– For keys, up to 15 mm glass, 10 mm plastic (key size dependent)
– For slider/wheel, up to 4 mm glass, 3 mm plastic
Key Sensitivity:
– Adjustable via change in sampling capacitor (Cs) value
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• Interface:
•
•
•
•
•
– SPI @ 750 kHz, CHANGE and DRDY status indicator pins
Moisture Tolerance:
– Increased moisture tolerance based on hardware design and firmware tuning
Power:
– 2.0 V to 5.5 V
Signal Processing:
– Self-calibration, autodrift compensation, noise filtering, patented Adjacent Key Suppression® (AKS®)
Package:
– 32-pin 5 x 5 mm MLF RoHS compliant
– 32-pin 7 x 7 mm TQFP RoHS compliant
Applications:
– Portable devices, domestic appliances and A/V equipment, PC peripherals, office equipment
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SNSA2
SNSKA2
SNSA3
SNSKA3
29 28 27 26 25
24
32 31 30
SNSKA1
SNSKB2
1
SNSB3
2
23
SNSA1
SNSKB3
3
22
SPREAD
VDD
4
21
VSS
VSS
5
20
CHANGE
SNSKB4
6
19
DRDY
SNSB4
7
18
VDD
SNSB5
8
17
9 10 11 12 13 14 15 16
SCK
MISO
MOSI
SS
SNSB7
SNSB6
SNSKB7
SNSKB6
QT2100
SNSKB5
1.2
RESET
Pinout Configuration
SNSB1
1.1
SNSKB
Pinout and Schematic
SNSB2
1.
Pin Descriptions
Table 1-1.
Pin Listing
Pin
Name
Type
Function
If Unused, Connect To...
1
SNSKB2
I/O
Sense pin. Connect to any CsB + Key
Open
2
SNSB3 (1)
I/O
Sense pin. Connect to CsB3
Open
3
SNSKB3
I/O
Sense pin. Connect to any CsB + Key
Open
4
VDD
P
Power
-
5
VSS
P
Ground
-
6
SNSKB4
I/O
Sense pin. Connect to any CsB + Key
Open
7
SNSB4
(1)
I/O
Sense pin. Connect to CsB4
Open
8
SNSB5 (1)
I/O
Sense pin. Connect to CsB5
Open
9
SNSKB5
I/O
Sense pin. Connect to any CsB + Key
Open
10
SNSKB6
I/O
Sense pin. Connect to any CsB + Key
Open
11
SNSKB7
I/O
Sense pin. Connect to any CsB + Key
Open
12
SNSB6 (1)
I/O
Sense pin. Connect to CsB6
Open
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Table 1-1.
1.
Pin Listing (Continued)
Pin
Name
Type
Function
If Unused, Connect To...
13
SNSB7 (1)
I/O
Sense pin. Connect to CsB7
Open
14
SS
I
SPI Slave Select (active low)
-
15
MOSI
I
SPI Master Out /Slave In
-
16
MISO
OF
SPI Master In/Serial Out
-
17
SCK
I
SPI Clock
-
18
VDD
P
Power
-
19
DRDY
OF
SPI Data Ready handshake line
Open
20
CHANGE
OF
State change notification
Open
21
VSS
P
22
SPREAD
23
24
Ground
-
OD
Spread-spectrum drive
Connect to Vdd (high) to enable
Connect to Vss (low) to disable
-
SNSA1 (1)
I/O
Sense pin. Connect to CsA1
Open
SNSKA1
I/O
Sense pin. Connect to any CsA + slider/wheel
Open
I/O
Sense pin. Connect to CsA2
Open
(1)
25
SNSA2
26
SNSKA2
I/O
Sense pin. Connect to any CsA + slider/wheel
Open
27
SNSA3 (1)
I/O
Sense pin. Connect to CsA3
Open
28
SNSKA3
I/O
Sense pin. Connect to any CsA + slider/wheel
Open
29
RESET
I
30
SNSB1 (1)
I/O
Sense pin. Connect to CsB1
Open
31
SNSKB1
I/O
Sense pin. Connect to any CsB + Key
Open
32
SNSB2 (1)
I/O
Sense pin. Connect to CsB2
Open
Reset (active low)
Vdd via resistor
SNS terminals can be paired with any SNSK terminals of the same group. For example, SNSA1 can be paired with
any SNSKA terminal.
I/O
CMOS input/output
I
CMOS input only
OD
CMOS open drain output (pull-up to Vdd)
OF
CMOS output that can float during Reset, Sleep or LP modes
P
Ground or power
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Schematic
Figure 1-1. Connection Diagram (32-MLF Package)
4
18
VDD
29
22
RESET
CsB1
SNSB1
SNSKB1
SPREAD
SNSB2
SNSKB2
SNSB3
SNSKB3
SNSB4
SNSKB4
SS
14
MOSI
15
MISO
16
SCK
17
DRDY
19
CHANGE
20
R4
SS
SNSB5
MOSI
SNSKB5
MISO
SNSB6
SCK
SNSKB6
DRDY
SNSB7
CHANGE
SNSKB7
30
QT Key
31
Key B2
CsB2
32
QT Key
Key B3
CsB3
2
SNSA2
GND
SNSKA2
SNSA3
5
VSS
VSS
SNSKA3
RsB3
QT Key
Key B4
3
CsB4
7
RsB4
QT Key
Key B5
6
CsB5
8
RsB5
QT Key
Key B6
9
CsB6
12
RsB6
QT Key
Key B7
10
CsB7
13
RsB7
QT Key
11
CsA1
SNSKA1
RsB2
1
R5
SNSA1
RsB1
23
RsA1
Wheel/Slider
24
CsA2
25
Ch1
RsA2
Ch2
26
CsA3
27
Ch3
RsA3
28
Voltage Regulator
VCC
C1
C2
Vin
GND
GND
R3
VDD
R2
VDD
Key B1
R1
21
1.3
Vout
VDD
C3
C4
GND
Important Design Guidelines:

The sensitivities of the various sense channels are determined by the values of the respective Cs capacitors
(that is, CsB1, CsB7, and so on); these values will require adjustment based on building a prototype product
and testing the sensitivity experimentally.

Signals DRDY and CHANGE may need pull-down resistors.
Re Figure 1-1, check the following sections for the variable component values:

Section 3.1 on page 9: Cs capacitors (CsB)

Section 3.2 on page 9: Sample resistors (RSNS)

Section 3.3 on page 9: Voltage levels
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2.
Overview
2.1
Introduction
The AT42QT2100 (QT2100) is an easy-to-use sensor IC based on the Atmel-patented charge-transfer (QT™)
principles for robust operation and ease of design. This device has many advanced features which provide for
reliable, trouble-free operation over the life of the product. In particular the QT2100 features advanced selfcalibration, drift compensation, and fast thermal tracking. The QT2100 can tolerate some fluctuations in the power
supply, and in many applications will not require a dedicated voltage regulator.
The QT2100 is capable of detecting near-proximity or touch on up to seven electrodes and a slider/wheel. It allows
electrodes to project sense fields through any dielectric such as glass or plastic. These electrodes are laid out as a
scroller (slider or wheel), plus seven additional independent keys.
Each key channel can be tuned for a unique sensitivity level by simply changing a corresponding external Cs
capacitor, whereas the slider/wheel sensitivity can be changed dynamically through SPI commands. Any number of
key channels can be optimized for operation as hand proximity sensors by increasing the sensitivity for the
corresponding channel.
Note:
There are special conditions if using AKS (see Section 4.3.6 on page 15).
The slider/wheel uses a simple, inexpensive sensing element between three connection points. The QT2100 can
report a single rapid touch anywhere along the sense elements, or it can track a finger moving along the
slider/wheel's surface in real time.
By using the charge-transfer principle, this device delivers a level of performance clearly superior to older
technologies yet is highly cost-effective. Spread-spectrum burst technology provides superior noise rejection.
2.2
Burst Operation
The device operates in burst mode. Each key is acquired using a burst of charge-transfer sensing pulses whose
count varies depending on the value of the sense capacitors (CsA1 to CSA3 and CsB1 to CSB7) and the load
capacitance Cx (finger touch capacitance and circuit stray capacitance).
The channels’ signals are acquired using three successive bursts of pulses:
Burst 1: B1, B2, B3
Burst 2: B4, B5, B6, B7
Burst 3: A1, A2, A3
where B1 to B7 are the individual key sensors and A1 to A3 are the slider/wheel sensors.
Bursts operate in sequence and occur one after the other with minimum delay. During each burst the DRDY pin is
held low. The groups are separated by an interval of 500 µs when DRDY is held high to signal an appropriate time for
SPI communications. Communications may be carried out at any time, however, regardless of the state of the DRDY
pin.
2.3
User Interface Layout and Options
The QT2100 can sense through all common plastics or glass or other dielectric materials up to 10 mm thick. It can be
used to implement a linear slider or rotary scroll wheel plus seven additional discrete keys. The slider or wheel
indicates absolute positions.
2.4
Slider and Wheel Construction
The QT2100 can be connected to a linear slider element (see Section 3.5 on page 10) or a wheel. Selection of linear
operation or wheel is set through an SPI command.
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2.5
Proximity Effect
Any number of keys can be programmed to have hand or body proximity. By using a relatively large electrode inside
the product enclosure and a larger value of CsB, the product can auto power up or activate its display with hand
approach. This simple feature can add enormous sales appeal to almost any product.However, if using AKS see
Section 4.3.6 on page 15.
2.6
Moisture Tolerance
The presence of water (condensation, sweat, spilt water, and so on) on a sensor can alter the signal values
measured and thereby affect the performance of any capacitive device. The moisture tolerance of QTouch devices
can be improved by designing the hardware and fine-tuning the firmware following the recommendations in the
application note Atmel AVR3002: Moisture Tolerant QTouch Design (www.atmel.com/Images/doc42017.pdf).
2.7
SPI Interface
The QT2100 is an SPI slave mode device, utilizing a four-wire full-duplex SPI interface.
In addition to the standard four SPI signals (SS, SCK, MOSI and MISO), there is a DRDY (data ready) output which
may optionally be used to time communications such that they do not occur during channel measurement bursts.
During each burst DRDY is held low by the QT2100. After each group burst, DRDY is driven high for 500 µs or until
3 bytes have been exchanged.
The QT2100 also provides a CHANGE signal to indicate when there has been a change in detection state. This
removes the need for the host to poll the QT2100 continuously.
On each SPI transfer the host sends three bytes to the QT2100 and the QT2100 simultaneously sends three bytes to
the host. The bytes sent from the host provide the QT2100 with all its configuration information; the bytes sent from
the QT2100 convey the states of the touch keys and slider or wheel.
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2.8
Operating Modes
The device features a number of operating modes to set the current drain and speed of response.
The available operating modes are:

Free Run Mode
This mode uses a continuous stream of acquire bursts. Free Run mode has, in consequence, the highest
power drain of all the QT2100 operating modes but the fastest response time.

LP Mode
In LP (low power) modes, the QT2100 spends a portion of the time sleeping to conserve power; it wakes
itself periodically to perform acquire bursts, then normally goes back to sleep again. The QT2100 provides
a choice of intervals between acquire bursts to allow an appropriate trade-off between speed and power to
be made for each product.

Sleep Mode
In Sleep mode, the QT2100 shuts down to conserve power; it remains in this mode, carrying out no
acquisition bursts until the host wakes it using the SS pin.

Sync Mode
In this mode the device synchronizes to the host in a way that allows for the suppression of heavy low
frequency noise; for example, from mains frequencies and their harmonics.
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3.
Wiring and Parts
3.1
Cs Sample Capacitors
The Cs (CsA1 to CSA3 and CsB1 to CSB7) sample capacitors accumulate the charge from the key electrodes and
determine sensitivity. Higher values of Cs make the corresponding sensing channel more sensitive. The values of Cs
can differ for each channel, permitting differences in sensitivity from key to key or to balance unequal sensitivities.
Unequal sensitivities can occur due to key size and placement differences and stray wiring capacitances. More stray
capacitance on a sense trace will desensitize the corresponding key; increasing the Cs for that key will compensate
for the loss of sensitivity.
The Cs capacitors can be virtually any plastic film or low to medium-K ceramic capacitor. Acceptable capacitor types
for most uses include PPS film, polypropylene film, and NP0 and X7R ceramics. Lower grade ceramics than X7R are
not advised; the X5R grade should be avoided because it is less stable than X7R. Larger values of Cs require better
quality to ensure reliable sensing
The normal Cs range is 1 nF to 100 nF for the keys and 4.7 nF to 220 nF for each channel of the slider or wheel for
good performance and position detection. The actual value used depends on the sensitivity required. A 3 nF to 5 nF
capacitor is typical for a touch key with an electrode diameter of 10 to 12 mm and a cover of 1 to 2 mm plastic, and
approximately 10 nF to 15 nF for slider or wheel electrodes.
3.2
Rs Series Resistors
Series Rs resistors (RsA1 to RSA3 and RsB1 to RSB7) are in-line with the electrode connections and are used to
limit electrostatic discharge (ESD) currents and to suppress radio frequency interference (RFI). For most
applications the Rs resistors will be in the range 4.7 k to 33 k each. In a few applications with low loading on the
sense keys the value may be up to 100 k.
Although these resistors may be omitted, the device may become susceptible to external noise or RFI. For details of
how to select these resistors refer to Application Note QTAN0079 Buttons, Sliders and Wheels Sensor Design
Guide.
3.3
Power Supply
The power supply can range from 2.0 V to 5.5 V. If this fluctuates slowly with temperature, the device will track and
compensate for these changes automatically with only minor changes in sensitivity. If the supply voltage drifts or
shifts quickly, the drift compensation mechanism will not be able to keep up, causing sensitivity anomalies or false
detections. In this situation a dedicated voltage regulator should be included in the circuit.
The QT2100 power supply should be locally regulated using a three-terminal device, to between 2.0 V and 5.5 V. If
the supply is shared with another electronic system, care should be taken to ensure that the supply is free of digital
spikes, sags, and surges, all of which can cause adverse effects.
For proper operation a 0.1 µF, or greater, bypass capacitor must be used between Vdd and Vss; the bypass
capacitor should be routed with very short tracks to the QT2100 VSS and VDD pins.
3.4
MLF Package Restrictions
The central pad on the underside of the MLF chip should be connected to ground. Do not run any tracks underneath
the body of the chip, only ground. Figure 3-1 shows an example of good and bad tracking.
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Figure 3-1. Examples of Good and Bad Tracking
Example of GOOD tracking
3.5
Example of BAD tracking
Slider and Wheel Construction
The QT2100 can be connected to a linear slider element or a wheel (see Figure 3-2). Selection of linear slider
operation or a wheel is set through an SPI command.
As with touch button electrodes, sliders and wheels can be constructed as etched areas on a PCB or flex circuit, or
from clear conductors such as Indium Tin Oxide (ITO) or screenprinted PEDOT to allow backlighting effects, or for
use over an LCD display.
Figure 3-2. All-Metal Slider and Wheel Construction
(Downloadable CAD files can be found on the Atmel website)
SNSA3
SNSA2
SNSA1
SNSA3
Tips of triangles should Position 0
be spaced  4 mm apart. SNSA3
 4 mm
 4 mm
0
1 to 126
127
Position (at 7 bits: 0 to 127)
Position 85
SNSA2
3.6
Position 43
SNSA1
Oscillator
No external oscillator is needed.
3.7
PCB Layout and Construction
Refer to Application Note QTAN0079, Buttons, Sliders and Wheels Sensor Design Guide and the Touch Sensors
Design Guide (both downloadable from the Atmel website), for more information on construction and design
methods.
The sensing channels used for the individual keys can be implemented as per the Touch Sensors Design Guide.
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3.8
PCB Cleanliness
Modern no-clean-flux is generally compatible with capacitive sensing circuits.
CAUTION: If a PCB is reworked to correct soldering faults relating to the QT2100, or to
any associated traces or components, be sure that you fully understand the nature of the
flux used during the rework process. Leakage currents from hygroscopic ionic residues
can stop capacitive sensors from functioning. If you have any doubts, a thorough
cleaning after rework may be the only safe option.
3.9
Spread-spectrum Circuit
The QT2100 offers the ability to spectrally spread its frequency of operation to heavily reduce susceptibility to
external noise sources and to limit RF emissions.
With this option enabled, bursts operate over a spread of frequencies, so that external fields will have minimal effect
on key operation and emissions are very weak. Spread-spectrum operation works together with the Detect Integrator
(DI) mechanism to dramatically reduce the probability of false detection due to noise.
Spread spectrum may be enabled by connecting the SPREAD pin to Vdd via a pull-up resistor, or disabled by
connecting to Vss via a pull-down resistor.
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4.
Detailed Operation
4.1
Reset
4.1.1
Introduction
When starting from power-up or RESET reset there are a few additional factors to be aware of. In most applications
the host will not need to take special action.
During hardware reset all outputs are disabled. To define the levels of the CHANGE and DRDY during reset these
signals should pulled down by resistors to 0 V. Otherwise, they may drift high causing the host to detect a false
logic 1.
When the initial reset phase ends, CHANGE and DRDY outputs are enabled. DRDY will drive low and CHANGE will
drive high.
4.1.2
Delay to SPI Functionality
The QT2100 SPI interface is not operational while the device is being reset. However, SPI is made operational early
in the start-up procedure.
After any reset (either via the RESET pin or via power-up), SPI typically becomes operational within 50 ms of RESET
going high or power-up. CHANGE is pulled high, and held high until the device status is read by the host microcontroller, to indicate completion of the initialization sequence after power-on or reset.
4.1.3
Reset Delay to Touch Detection
After power-up or reset, the QT2100 calibrates all electrodes.
During this time, touch detection cannot be reported. Calibration completes after 15 burst cycles, which takes
approximately 350 ms, depending on the electrode layout and Cs selection.
In total, 400 ms are required from reset or power-up for the device to be fully functional.
4.1.4
Disabled Keys:
Keys with missing Cs capacitors, or that otherwise have an out-of-range signal during calibration, are considered to
be unused or faulty and are disabled. Disabled keys are re-examined for operation after each reset or recalibration
event.
4.1.5
Mode Setting After Reset
After a reset the device will enter Free Run mode, with AKS disabled.
4.2
Communications
4.2.1
Introduction
The QT2100 communicates as a slave device over a full-duplex 4-wire (MISO, MOSI, SCK, SS) SPI interface. In
addition there is a DRDY pin which indicates when the QT2100 is carrying out acquisition bursts and a CHANGE pin
which is asserted when a change occurs in the status of the touch sensors (see Table 4-1).
Table 4-1.
Additional Pins
Pin
High
Low
DRDY
Burst is complete
Burst is active
CHANGE
New touch data
Latest data has already been
read by host
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See Section 6.5 on page 32 for details of the SPI Configuration and Timing Parameters.
The host must always transfer three bytes in succession within the allotted time (10 ms maximum). If all bytes are
not received in this interval it is treated by the QT2100 as an error. In this case the exchange is reset and the next
read will contain the first data byte of a new exchange.
Messages from the host to the QT2100 carry configuration information; return data from the QT2100 carries key
state information. For details of the message contents see Section 5. on page 19.
Figure 6-1 and Figure 6-2 on page 33 show the basic timing for SPI operation. The host does the clocking and
controls the timing of the transfers from the QT2100. Transfers are always clocked as a set of three bytes, Byte 1, 2,
and 3.
DRDY stays high for 500 µs. It falls again after Byte 3 has shifted to indicate completion. DRDY goes high after each
burst.
After the host asserts SS low, it should wait >22 µs in low power mode before starting SCK; in Free run mode, a
delay of 2 µs is sufficient. The QT2100 reads the MOSI pin with each rising edge of SCK, and shifts data out on the
MISO pin on falling edges. The host should do the same to ensure proper operation.
Between the end of the Byte 1 shift and the start of the Byte 2 shift (and between Byte 2 and Byte 3), the host may
raise SS again, but this is not required. SS should be held high when not communicating; if SS is low this is taken as
an indication of impending communications.
In this case, extra current is drawn, as the QT2100 does not enter its lowest power sleep mode.
All timings not mentioned above should be as in Figure 6-2 on page 33.
4.2.2
Change Pin
The QT2100 has a CHANGE output pin which allows for key state change notification. Use of the CHANGE signal
relieves the host of the burden of regularly polling the QT2100 to get key states. CHANGE goes high when an event
occurs that causes a change to the contents of the Normal Data bytes; that is, when a new key is pressed, or
released, or a movement is detected on the slider/wheel.
Similarly, when a custom threshold or LPM is sent to the QT2100, the CHANGE line is asserted to indicate that the
new setting has been applied and is shown in the Normal Exchange data.
CHANGE also goes high after a reset to indicate to the host that it should do an SPI transfer in order to provide initial
configuration information to the QT2100 (as it does on every SPI transfer).
CHANGE is driven low only once the data has been read through an SPI transfer.
In the case of a transient touch on one of the sensors, in which the touch has been removed before the host has read
the status of the sensors, the Change line remains asserted.
Note:
4.2.3
In this case the data that will be read may be identical to the data that was previously read.
DRDY Pin
The Data Ready (DRDY) pin is a quick indication of the QT2100 activity. During channel acquisition bursts the pin is
held low by the device, and driven high for ~500 µs in between bursts. During processing and sleep the pin is driven
high continuously, unless a 3-byte communications exchange has taken place since the last acquisition burst.
After a 3-byte exchange has completed the pin is pulled low and remains low until the next burst completion, after
which the normal cycle resumes. This allows the host to detect if the 3-byte exchange packets have become
de-synchronized.
The QT2100 has a DRDY grace period. If communications start during the 20 µs after DRDY has been deasserted
(pulled low) by the QT2100, then DRDY is reasserted and held high until the exchange is complete. Key
measurement bursts do not take place during this time.
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Figure 4-1. DRDY Cycle without Communications
Burst 1
Burst 2
Burst 3
Processing
& Sleep
Burst 1
Burst 2
Burst 3
Burst 3
Processing
& Sleep
Burst 1
Burst 2
Burst 3
DRDY
Burst 1
Burst 2
Burst 3
Figure 4-2. DRDY Cycle with Communications
Burst 1
Burst 2
DRDY
Burst 1
Burst 2
Burst 3
SCK
4.3
Signal Processing
4.3.1
Power-up Self-calibration
On power-up, or after reset, all 10 channels are typically calibrated and operational within 350 ms.
4.3.2
Drift Compensation
This operates to correct the reference level of each key automatically over time; it suppresses false detections
caused by changes in temperature, humidity, dirt and other environmental effects.
The QT2100 drifts towards touch at a rate limited to 1 count every 3 seconds, and away from touch at a rate limited
to 1 count every 0.5 s. Reference drift is paused during touch detection, and for 2 s after touch detection ends. These
timings may be slower in Sync mode, or where asynchronous acquisition is triggered with LPB, as timing calculations
are derived from the acquisition interval.
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4.3.3
Detection Integrator Filter
Detect Integrator (DI) filter confirmation reduces the effects of noise on key states. The DI mechanism requires a
specified number of measurements that qualify as detections (and these must occur in a row) or the detection will not
be reported.
In a similar manner, the end of a touch (loss of signal) also has to be confirmed over several measurements.
The QT2100 provides a choice of either two or six DI measurements.
4.3.4
Adjacent Key Suppression (AKS)
This patented feature works to prevent multiple keys from incorrectly responding to a single touch. This can happen
with closely spaced keys, or a scroll wheel that has buttons very near.
Adjacent Key Suppression (AKS) operates by comparing signal strengths from keys within a group of keys to
suppress touch detections from those that have a weaker signal change than the dominant one.
When enabled globally on the QT2100, AKS allows only one key or the scroll section to indicate a touch at a time.
The QT2100 has a range of preset AKS groupings, where only one key in an AKS group can indicate a touch at any
time while keys in different groups can indicate touch in any combination.
AKS can also be disabled.
4.3.5
Autorecalibration (MOD)
The device can time out and recalibrate all sensors after a continuous touch detection that lasts for the chosen
Maximum On Duration (MOD). This ensures that a key can never become stuck on due to foreign objects or other
external influences. After recalibration the key will resume normal functionality.
The nominal delay is selectable to be 10 s, 20 s, 60 s, or infinite (disabled) though the actual delay is different in
Sleep mode, as timing is entirely driven by host communications.
The device also automatically recalibrates a key when its associated signal reflects a sufficient decrease in
capacitance from the reference level (signal error). In this case, unlike MOD recalibration, only the key that shows a
signal error is recalibrated.
This recalibration is triggered when the decrease in capacitance is seen on the key signal for more than 1.5 s.
4.3.6
Proximity Sensor
Any key can be optimized for operation as a hand proximity sensor. The sensitivity can be increased by a higher
value of Cs.
However, If using AKS only channel seven can be used as a proximity sensor and the AKS bits should be set to 101,
to ensure that the proximity key does not lock out other keys or the slider/wheel (see Table 5-2 on page 20).
Design of proximity electrodes requires care, so as to ensure that the electrode area is maximized whilst ensuring
adequate and easy coupling to a hand as it approaches the equipment.
4.3.7
Faulty and Unused Keys
Any sense channel that does not have its sense capacitor (Cs) fitted is assumed to be either faulty or unused. A
sensor fault is detected by an out-of-range signal count during calibration, where the minimum allowed signal is 32
counts and the maximum is 8192. This channel takes no further part in operation unless a host-commanded
recalibration operation shows it to have an in-range burst count again.
This is important for sense channels that have an open or short circuit fault across Cs. Such channels would
otherwise cause very long acquire bursts, and in consequence would slow the operation of the device. Note that
acquisition pulses will still be generated on these channels, but no measurements of their state will be carried out.
The burst will finish when all the enabled channels on the burst group have completed acquisition.
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4.4
Operating Modes
4.4.1
Introduction
Four basic operating modes are possible: Free Run, Low Power (LP), Sleep and Sync. Sleep is a special case of
LP mode, where the sleep time is infinite. Sync is a special case of LP mode where the timing of host
communications is used as the timing basis for the QT2100 acquisition cycle. In the absence of host
communications, the device operates in its most power-efficient low power mode, LP Mode 4. See below for further
details.
4.4.2
Free Run Mode
In this mode the device operates continuously with short intervals between burst groups; there are three bursts, one
burst for each electrode group. DRDY goes high for approximately 500 µs between bursts and stays high during
signal processing.
In this mode, the acquisition bursts are unsynchronized, making this mode unsuitable if synchronization to mains
frequency is needed.
4.4.3
Low Power Mode
LP mode is designed to allow low power operation while still retaining full operation but at a slower speed. This mode
is useful for devices that must use the touch keys to wake up a product, yet minimize power consumption.
Several LP timings allow the user to trade power versus response time: the slower the response time, the lower the
power consumed.
In LP mode, the device spends a portion of the time sleeping between bursts; it wakes periodically to measure all
channels with a set of three acquisition bursts, then goes back to sleep.
If a touch is detected, the device operates as in Free Run mode and attempts to perform the Detect Integrator (DI)
noise filter function to completion; if the DI filter fails to confirm a detection the device goes back to sleep and
resumes LP mode. During the DI function the LPS bit will be cleared.
If a key is found to be in detection the CHANGE pin will go high and the part will remain in Free Run mode. To go
back into LP mode the host has to request LP mode again with an SPI communications exchange after the touch
detection has been cleared by removal of touch or recalibration.
CHANGE Pin in LP Mode: During the sleep portion of LP mode, CHANGE is held low.
If however a change of key state is confirmed, CHANGE goes high and the part runs from then on in Free Run mode
until the host reads the key state and puts the device back into LP mode or some other mode.
MISO in LP Mode: During the sleep portion of LP mode, MISO floats.
DRDY during LP Mode: DRDY remains high while the QT2100 is sleeping, to indicate to the host that SPI
communications are possible. During an actual acquire burst, DRDY is held low.
Command During LP Mode: The device can be woken from sleep by the SS pin being pulled low. Note that the SS
pin must be pulled high in order for the device to enter its lowest power sleep mode. If SS is held low, the device
enters a higher power sleep mode to enable SPI communications. The host may perform a normal SPI transfer as
shown in Figure 4-3 on page 17.
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Figure 4-3. LP Mode SPI Operation
SPI Operation with LPB = 0
No SPI Communication
SPI Communication
Acquire Bursts
>22us
/SS from host
SCLK from Host
Host Data Output
(QT2100 Input - MOSI)
don't care
don't care
don't care
don't care
don't care
don't care
command bytes
response bytes
QT Data Output
(QT2100 Out - MISO)
3-state
3-state
SPI Operation with LPB = 1
Acquire Bursts
>22us
/SS from host
SCLK from Host
Host Data Output
(QT2100 Input - MOSI)
command bytes
response bytes
QT Data Output
(QT2100 Out - MISO)
Note:
3-state
3-state
don't care
don't care
With LPB = 1, a pulse on SS with or without communications triggers an acquisition burst
to follow communications. Pulse width > 22 µs.
After the SPI transfer is completed, the QT2100 will generate a set of three acquire bursts if LPB = 1, during which
DRDY will be low.
The mode and options settings sent from the host to the QT2100 during the SPI transfer take effect after the set of
acquire bursts.

If either LP mode or Sleep mode is selected, the QT2100 will go back to sleep with DRDY high provided no
key is detected as possibly touched.

If Sync mode is selected, the QT2100 will go back to sleep with DRDY high provided no key is detected as
possibly touched.
The CHANGE pin will go high at this time if a key is confirmed as touched.
SS Wake pulse: In LP Mode, a wake pulse may be used on the SS pin to either trigger an LPB acquire burst or to
wake the device in advance of communications. The pulse should be at least 22 µs in duration.
When used prior to communications, there should be a delay of 100 µs to 1 ms between the end of the SS Pulse and
the following SS assertion.
4.4.4
Sleep Mode
Sleep mode offers the lowest possible current drain, in the low microamp region.
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Sleep mode is a special case of LP mode, where the sleep duration between bursts is infinite. All comments
concerning LP mode, including about SPI communications, apply equally to Sleep mode, except that the LPB bit is
ignored and bursts are always generated after an SPI transfer or SS wake pulse as if LPB = 1.
Note:


In Sleep mode the QT2100 only performs acquisition bursts following being woken by SS. This has
two effects:
Touch detection only occurs following SS-wake pulses, and hence CHANGE can only go high at that time.
The QT2100 cannot drift its internal references unless the host sends periodic SS-wake pulses. If the host
does not do this, then it should command the QT2100 to recalibrate when it sets the QT2100 into a different
operating mode.
This mode can be used by the host to create its own LP Mode timings via the SS wakeup pulse method.
4.4.5
Sync Mode
This mode is useful for low frequency noise suppression, for example from mains frequencies in line-operated
appliances. Acquisition bursts are synchronized to the SS-wake pulses from the host.
Sync mode is very similar to LP Mode 4, with two differences:

It does not operate as in Free Run mode when a touch is first detected

The LPB bit is ignored and a burst is always generated after each SS wakeup or SPI transfer as if LPB = 1
Not operating as in Free Run mode when a touch is first detected (before DI confirmation has taken place) means
that acquisition bursts are restricted to the immediate time after a sync signal (SS), heightening the effect of low
frequency noise suppression.
In many applications of Sync mode the DI filter will need to be set to two counts, to avoid the QT2100 response time
being unacceptably lengthened as a consequence of this.
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5.
SPI Commands
5.1
Introduction
Each communication exchange between the QT2100 and the host device consists of 3 bytes transmitted each way.
The host controls the clock signals and the timing of the exchange.
The data sent by the host indicates the command mode and the device settings where appropriate. There are four
command modes, selectable through bits 5 – 7 of the first byte (byte 0, Req bits):

Normal Exchange mode (Req = 000)

Custom Threshold command mode (Req = 100)

Send Signal command mode (Req = 001)

Device Version command mode (Req = 010)
The device settings sent by the host in its three command bytes becomes effective immediately after all three bytes
are received by the QT2100. The response to these three bytes is three data bytes containing key detection
information.
5.2
Normal Exchange Mode
5.2.1
Introduction
The Normal Exchange mode (Req = 000) is the normal mode for communication between the host and the device.
Data is sent every time an SPI communication occurs in Normal Exchange mode. If one of the other commands is
sent by the host, the corresponding response will be sent during the subsequent 3-byte exchange.
This Normal Exchange response forms the default (start-up) QT2100 data.
5.2.2
Host Data
In Normal Exchange mode (Req = 000) the host sends the 3-byte data in Table 5-1.
Table 5-1.
Host
Byte
Normal Exchange Mode – Host Command Bytes
Bit
7
0
1
2
Note:
6
5
Req = 000
0
MOD
Resolution
4
3
2
1
0
PROX
SLD
AKS
DI
LPB
LP Mode
CalW
CalK
Cal Key Num
Bits labelled 0 should not be altered
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Byte 0
AKS – Three bits used to determine the AKS mode, as shown in Table 5-2 (see Section 4.3.4 on page 15
for further information).
Table 5-2.
AKS Mode
AKS Bits
AKS Option
000
AKS disabled (default)
001
AKS global: All 7 keys + slider/wheel are in the same group
AKS group 1: all keys
010
AKS group 2: slider/wheel
AKS group 1: keys 1 – 4
011
AKS group 2: keys 5 – 7
AKS group 3: slider/wheel
AKS group 1: keys 1 – 4
100
AKS group 2: keys 5 – 7 + slider/wheel
AKS group 1: keys 1 – 6 + slider/wheel
101
AKS group 2: key 7
SLD – Scrolling device type selection.
SLD = 0: Wheel mode (default)
SLD = 1: Linear slider mode
PROX – This setting is included to ensure compatibility with host drivers designed for the QT1106. Any key
may be optimized as a proximity sensor but key 7 should be used in any application where AKS is required,
as it can be excluded from AKS by selecting AKS mode 101.
Req – Set to 000 to indicate Normal Exchange mode.
Byte 1
LP Mode – After each measurement and processing cycle the device goes to sleep for a period, the
duration of which is set by the LP mode as per Table 5-3.
Table 5-3.
Sleep/Low Power Modes
LP Mode Bits
Operating Mode
000
Free run – 0 ms sleep period in each cycle (default):
Acquisition and processing carried out continuously with no sleep. This
mode has the highest power consumption, but the quickest response.
001
60 ms sleep period in each cycle
010
120 ms sleep period in each cycle
011
240 ms sleep period in each cycle
100
480 ms sleep period in each cycle
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Table 5-3.
Sleep/Low Power Modes (Continued)
LP Mode Bits
Operating Mode
101
Sync mode:
The QT2100 performs an acquisition burst when triggered by a rising edge
on SS and ‘heartbeat’ bursts at the same interval as LP Mode 4
110
Sleep:
The QT2100 performs an acquisition and processing cycle only when
triggered by a rising edge on SS, whether a low pulse or a communication
exchange.
111
Reserved
LPB – Sets the LP mode following burst option. See Figure 4-2 on page 14.
LPB = 0: If the host communicates with the device, or there is an SS pulse during any LP mode (modes
001 to 100), there will be no following burst. The only bursts that will take place are those that occur as
naturally defined by the LP mode noted above.
LPB = 1: If the host communicates with the device, or there is an SS pulse during any LP mode (modes
001 to 100), there will be an additional burst following SS raising high (default).
In modes 101 (Sync) and 110 (Sleep), there will always be a burst following SS raising high, regardless of
the LPB Setting. See Table 5-3 for a description of the Mode settings.
DI - Set the Detect Integrator noise filter function.
DI = 0: Two detections required to confirm a touch (faster but less noise immune).
DI = 1: Six detections required to confirm a touch (slower but more noise immune; appropriate for most
applications) (default).
MOD (Recal Time) – Sets the Maximum On-duration for all keys and slider/wheel. Controls the time from
the start of a detection to automatic recalibration of all channels. See Table 5-4 for allowed MOD times.
Table 5-4.
Maximum On-duration in Free Run Mode
MOD Bits
Maximum On-duration
00
10 s (default)
01
20 s
10
60 s
11
Infinite MOD – timeout disabled
Note: in Sleep mode, all device timing is dependent on the regularity of SPI communications. See Section
4.4.4 on page 17 for more information.
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Byte 2
Cal Key Num – key to be recalibrated when CalK = 1 (see Table 5-5).
Table 5-5.
Key Recalibration
Cal Key Num Bits
Key
000
Recalibrate all keys (excluding slider/wheel)
001
Recalibrate Key 1
010
Recalibrate Key 2
011
Recalibrate Key 3
100
Recalibrate Key 4
101
Recalibrate Key 5
110
Recalibrate Key 6
111
Recalibrate Key 7
CalK – Recalibrates the key(s) specified by Cal Key Num.
CalK = 0: No recalibration (normal state of this bit).
CalK = 1: The device recalibrates key(s).
CalW – Recalibrates the slider/wheel.
CalW = 0: No recalibration (normal state of this bit).
CalW = 1: The device recalibrates the slider/wheel.
Set CalK/CalW only once when required, and set CalK/CalW = 0 thereafter. If the bit is constantly set to 1,
the device will keep recalibrating and will never detect a touch.
Note that the device recalibrates automatically on power-up, so that the use of Recal should rarely be
required. Any channel used as a proximity detector should be recalibrated soon after each proximity
detection, to ensure stability.
Resolution – the resolution of the slider/wheel reported position (see Table 5-6 and Figure 5-1).
Table 5-6.
Resolution
Resolution Bits
Resolution
000
Reserved
001
2 Bits: 4 positions (0 – 3)
010
3 Bits: 8 positions (0 – 7)
011
4 Bits: 16 positions (0 – 15)
100
5 Bits: 32 positions (0 – 31)
101
6 Bits: 64 positions (0 – 63)
110
7 Bits: 128 positions (0 – 127) (default)
111
8 Bits: 256 positions (0 – 255)
Note: A resolution change will only become effective on the next touch.
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Figure 5-1. Slider and Wheel Resolution
Slider M ode
W heelM ode
SNSKA
SNSA3
SNSKA
SNSA3
SNSKA
SNSA1
2 bits
1
0
SNSKA
SNSA3
3 bits
SNSKA
SNSA2
1
SNSKA
SNSA2
3
2
4
SNSKA
SNSA2
SNSKA
SNSA3
SNSKA
SNSA1
5
6
0
1
2
3
4
5 6
SNSKA
SNSA2
7
8
2
1
SNSKA
SNSA3
9 10 11 12 13 14
SNSKA
SNSA1
SNSKA
SNSA3
7
1
6
SNSKA
SNSA2
15
SNSKA
SNSA3
0
5
4 bits
0
2 bits
7
SNSKA
SNSA3
3
3
2
SNSKA
SNSA1
0
SNSKA
SNSA3
2
3
4
SNSKA
SNSA1
14 15 0 1
13
2
3
12
4
11
5
10
9 8 7 6
SNSKA
SNSA2
SNSKA
SNSA1
4 bits
3 bits
N ote: the first and last slider positions
(shaded) have larger touch areas.
5.2.3
QT2100 Data
The three return bytes contain the response to the previously sent command. Initially it is assumed that the
previously sent command was a Normal Exchange command. The return bytes for the Normal Exchange command
is shown in Table 5-7.
Table 5-7.
Normal Exchange Mode – Return Bytes
Bit
QT2100
Byte
7
6
5
4
3
2
1
0
0
CW
CK
EW
EK
LPS
PM
0
CTL
1
W
K7
K6
K5
K4
K3
K2
K1
2
Position
Byte 0
CTL: Custom Threshold Loaded: If CTL = 1, a custom slider/wheel threshold has been loaded from the
host. This is set as a result of a Custom Threshold command. Once the QT2100 has received a custom
threshold, this bit is set and stays set until reset.
PM: Proximity Mode: This setting is disabled as there is no proximity mode on the QT2100 because each
key can be configured as a proximity sensor. This setting has been left to ensure compatibility with the
QT1106.
LPS: LP/Sleep State: If LPS = 1, the device was in LP, Sync, or Sleep mode when the requesting
command was received. If LPS = 0, the device was in Free Run mode.
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EK: Key(s) in Error: If EK = 1, there is a sufficient decrease in capacitance of one or more normal key(s)
from the reference level. The affected key will be recalibrated if this condition is seen for more than 1.5
seconds.
EW: Slider/Wheel in Error: If EW = 1, there is a sufficient decrease in capacitance of the slider/wheel from
the reference level. The slider/wheel will be recalibrated if this condition is seen for six successive cycles.
CK: Key(s) in Calibration: If CK = 1, one or more key(s) are being calibrated.
CW: Slider/Wheel in Calibration: If CW = 1, the slider/wheel is being calibrated.
Byte 1
K1 – K7: Contains the key states of each key. A 1 in a bit position means the key is confirmed as being
touched.
W: The state of the wheel/rotor. A 1 means the slider/wheel is confirmed as being touched.
Byte 2
Position: The position of touch on the slider/wheel. If the slider/wheel is not being touched, the position will
be the position of the last touch.
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5.3
Custom Threshold
5.3.1
Introduction
The Custom Threshold command mode (Req = 100) is used to modify the detection threshold of the slider/wheel. It
only needs to be sent once, for the new value to take effect, and then the Normal Exchange mode resumes (see
Section 5.2 on page 19). The new value will be in use until the chip is reset or a new custom threshold is sent.
5.3.2
Host Data
In Custom Threshold command mode the host sends the 3-byte data in Table 5-8.
Table 5-8.
Custom Threshold Command Mode – Host Command Bytes
Bit
Host
Byte
7
0
6
5
Req = 100
1
3
2
1
0
0
0
0
0
0
0
0
0
T1 – Slider/Wheel Threshold
2
Note:
4
0
0
0
0
0
Bits labelled 0 should not be altered
Byte 0
Req – Set to 100 to indicate Custom Threshold command mode.
Byte 1
T1: Custom threshold value of the slider/wheel. Higher numbers are less sensitive. Touch detection uses
this threshold combined with a hysteresis equal to 25% of the threshold (with a minimum hysteresis value of
one).
Power-up default setting: 30
Note: Custom Threshold Command is only used if the detection threshold of the slider/wheel needs to be
changed from the power-up default.
Byte 2
Always set to 0.
5.3.3
QT2100 Data
The QT2100 response to the Custom Threshold command is the Normal Exchange report.
Once the custom thresholds have been set, the CTL bit in the Normal Exchange report is set to 1 to indicate that the
changed threshold has been applied (see Table 5-7).
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5.4
Send Debug Data
5.4.1
Introduction
In a Send Debug Data exchange (Req = 001) the host requests the QT2100 to send 16-bit debug data on the next
3-byte exchange.
5.4.2
Host Data
In Send Debug Data command mode the host sends the 3-byte data in Table 5-9.
Table 5-9.
Host
Byte
Send Debug Data Command Mode – Host Command Bytes
Bit
7
0
6
5
Req = 001
4
3
2
1
0
0
0
0
0
Debug
Data
0
0
1
0
0
0
0
2
0
0
0
0
Note:
Channel
0
0
Bits labelled 0 should not be altered
Byte 0
Debug Data: 1 bit, specifying the debug data that should be returned. Either of two 16-bit debug data states
may be requested:
Debug Data = 0: Reference – the reference level used by the QT2100 for comparison with the current
measurements to detect touch. The reference value is a 16-bit unsigned integer.
Debug Data = 1: Delta – the difference between the reference level and the current level, indicating how
close the channel is to detecting touch. The delta value is a 16-bit signed integer.
Req: Set to 001 to indicate Send Debug Data command mode.
Byte 1
Channel: 4 bits indicating the measurement channel for which the Send Debug Data is requested.
Channels are mapped to keys or slider/wheel electrodes, as in Table 5-10.
Table 5-10. Channel Mappings
Channel
Sensing Object
0
Key B1
1
Key B2
2
Key B3
3
Key B4
4
Key B5
5
Key B6
6
Key B7
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Table 5-10. Channel Mappings (Continued)
Channel
Sensing Object
7
Slider/Wheel A1
8
Slider/Wheel A2
9
Slider/Wheel A3
Byte 2
Always set to 0.
5.4.3
QT2100 Data
During this exchange, the QT2100 returns the data requested on the previous exchange (Normal Data by default),
and at the next exchange the requested debug data is returned.
Table 5-11. Send Debug Data Command Mode – Return Bytes
QT2100
Byte
Bit
7
6
5
4
3
0
State of Channel
1
LSB Delta/LSB Reference
2
MSB Delta/MSB Reference
2
1
0
Byte 0
State of Channel: Indicates the current state of the channel.
Table 5-12. Sensor States
State Code
Sensor State
0x01
Calibration
0x02
No Detect (no touch)
0x04
Filter In (to confirm touch)
0x08
Detect (touched)
0x10
Filter out (to confirm release)
0x20
Recal (positive error recalibration)
0x40
Fault Check
Byte 1
LSB Delta/LSB Reference: The least significant 8 bits (LSB) of the Reference/Delta signal.
Byte 2
MSB Delta/MSB Reference: The most significant 8 bits (MSB) of the Reference/Delta signal.
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5.5
Device Version
5.5.1
Introduction
In a Device Version exchange (Req = 010) the host requests the QT2100 to send the device ID and Firmware
version information.
5.5.2
Host Data
In Device Version command mode the host sends the 3-byte data in Table 5-13.
Table 5-13. Device Version Command Mode – Host Command Bytes
Bit
Host
Byte
7
0
6
5
Req = 010
4
3
2
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
2
0
0
0
0
0
0
0
0
Note:
Bits labelled 0 should not be altered
Byte 0
Req: Set to 010 to indicate Device Version command mode.
Byte 1
Always set to 0.
Byte 2
Always set to 0.
5.5.3
QT2100 Data
During this exchange, the QT2100 returns the data requested on the previous exchange (Normal Data by default),
and at the next exchange the requested data is returned.
Table 5-14. Device Version Command Mode – Return Bytes
QT2100
Byte
Bit
7
6
5
0
1
4
3
2
1
0
Device ID = 108 (0x6C)
Version Major
2
Version Minor
Build
Byte 0
Device ID: the device ID; always 108 (0x6C)
Byte 1
Version Major: 4 bits, indicating the major version of the device.
Version Minor: 4 bits, indicating the minor version of the device.
For example, firmware version 1.0 would be indicated as 0x10.
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Byte 2
Build: The build of this firmware version.
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6.
Specifications
6.1
Absolute Maximum Specifications
VDD
–0.3 to +6.0 V
Max continuous pin current, any control or drive pin
±20 mA
Short circuit duration to ground or Vdd, any pin
Infinite
Voltage forced onto any pin
–0.3 V to (Vdd + 0.3) V
CAUTION: Stresses beyond those listed under Absolute Maximum Specifications may cause permanent damage to
the device. This is a stress rating only and functional operation of the device at these or other conditions beyond
those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum
specification conditions for extended periods may affect device reliability
6.2
Recommended Operating Conditions
Operating temperature
–40°C to +85°C
Storage temperature
–50°C to +125°C
VDD
+2.0 to 5.5 V
Short-term supply ripple + noise
±20 mV / s
Long-term supply stability
±100 mV
Cs range, keys
1 to 100 nF
Cs range, slider/wheel
4.7 to 220 nF
Cx range
0 to 50 pF
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6.3
AC Specifications
Vdd = 5.0V, Cs keys = 4.7 nF, Cs slider/wheel = 15 nF; circuit of Figure 1-1
Parameter
Description
Min
Typ
Max
Units
Notes
Tsu
Start-up to SPI time
–
50
60
ms
From cold start
Trc
Recalibration time
–
300
–
ms
Depends on ground loading of
electrodes and Cs selection
Fc
Burst center frequency
–
100
80
–
kHz
Spread spectrum disabled
Spread spectrum enabled
Fm
Burst modulation, percent
–
15
–
%
Total deviation
Tpc
Sample pulse duration
–
2.66
5.85
–
µs
Spread spectrum disabled
Spread spectrum enabled
Tbd
Acquire burst duration
–
20
25
–
ms
Spread spectrum disabled
Spread spectrum enabled
(Total for all 3 acquire burst groups)
Tdf6
Response time – Free Run
mode, DI 6 samples
–
120
–
ms
Spread spectrum disabled
Tdf2
Response time – Free Run
mode, DI 2 samples
–
40
–
ms
Spread spectrum disabled
Tdl
Response time – LP mode
–
280
–
ms
LP Mode 2, DI = six counts
Tdr
Release time – all modes
–
40
–
ms
End of touch
6.4
DC Specifications
Vdd = 5.0V, Cs keys = 4.7 nF, Cs slider/wheel = 15 nF; circuit of Figure 1-1
Parameter
Description
Min
Typ
Max
Units
Vil
Low input logic level
0
–
0.3 × Vdd
V
Vhl
High input logic level
0.7 × Vdd
–
Vdd
V
Vol
Low output voltage
–
–
0.5
V
Voh
High output voltage
Vdd – 0.5
–
–
bits
Iil
Input leakage current
–
–
±1
µA
Ar
Acquisition resolution
–
14
–
bits
External reset low pulse width
2
–
–
µs
Trst
Notes
7 mA sink
2.5 mA source
AT42QT2100 [DATASHEET]
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6.5
SPI Bus Specifications
Parameter
Specification
Data bits
8 data bits
Shift out on falling edge
Data transmission
Shift in on rising edge
Three bytes per transmission, byte 1 most significant bit sent first
Clock idle
Clock idle high
Maximum clock rate
750 kHz
Minimum time between exchanges
500 µs
Figure 6-1. Data Byte Exchange – Signals
SCK
SAMPLE
MOSI/MISO
CHANGE
MOSI PIN
CHANGE
MISO PIN
SS
MSB
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
LSB
AT42QT2100 [DATASHEET]
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Figure 6-2. Data Byte Exchange – Timings
SS must be held
low between
bytes of an
exchange.
Period
Min
Max
Unit
SS Low to SCK – Free-run mode
2
–
µs
SS Low to SCK – LP mode
22
–
S2
SCK to SS High
20
S3
SCK Low Pulse
S4
SCK High Pulse
S5
SCK Period
General
Min
Max
Unit
Rise/Fall Time
–
1600
ns
µs
Setup
10
–
ns
–
µs
Hold
333
–
ns
666
–
ns
666
–
ns
–
ns
–
µs
20
ns
S1
6.6
S6
Between Bytes
S7
SS High to Tristate
External Reset
Parameter
VRST
6.7
–
Description
Operation
Threshold voltage low (Activate)
Threshold voltage high (Release)
0.2 × Vdd
0.9 × Vdd
Internal Resonator
Parameter
Operation
Internal RC oscillator
8 MHz with spread-spectrum modifier during measurement
bursts, if enabled
AT42QT2100 [DATASHEET]
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6.8
Signal Processing
Vdd = 5.0V, Cs keys = 4.7 nF, Cs slider/wheel = 15 nF; circuit of Figure 1-1
Description
Min
Units
Notes
Detection threshold (keys)
10
counts
Threshold for increase in Cx load
Detection threshold (slider/wheel)
30
counts
Changeable through SPI
Detection hysteresis (keys)
2
counts
Detection hysteresis (slider/wheel)
5
counts
DI filter, start of touch, normal mode
6
samples
Must be consecutive or detection fails
DI filter, start of touch, fast DI mode
2
samples
Must be consecutive or detection fails
6.9
Power Consumption
6.9.1
Spread Spectrum Disabled
Table 6-1.
25 percent of slider/wheel detection threshold
Power Consumption (µA)
Vdd
Note:
LP Mode
2V
3.3 V
5V
0
950
1940
4350
1
190
420
1050
2
95
205
640
3
60
120
320
4
40
80
200
Sleep
15
18
22
Power measurements taken 4.7 nF capacitors on the keys and 15 nF capacitors on the slider electrodes.
Figure 6-3. Idd Curve
Vdd = 2V
Vdd = 3.3V
Vdd = 5V
Current (uA)
5000
4000
3000
2000
1000
0
0
1
2
3
4
LP Mode
AT42QT2100 [DATASHEET]
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Spread Spectrum Enabled
Table 6-2.
Power Consumption (µA)
Vdd
Note:
LP Mode
2V
3.3 V
5V
0
955
2050
4450
1
210
510
1250
2
105
260
760
3
65
150
390
4
40
95
235
Sleep
10
18
22
Power measurements taken 4.7 nF capacitors on the keys and 15 nF capacitors on the slider electrodes.
Figure 6-4. Idd Curve
Vdd = 2V
Vdd = 3.3V
Vdd = 5V
5000
Current (uA)
6.9.2
4000
3000
2000
1000
0
0
1
2
3
4
LP Mode
AT42QT2100 [DATASHEET]
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6.10
Mechanical Dimensions
6.10.1 32-pin 5 x 5 mm MLF
;
(
);(
;(O
(
&%
;(O
$
N
+#+B %%$;($);%$)
6<?8@!!9
;$
$%
A
+#B+
+#BC
#++
+#++
+#+
+#+C
D
+#EC
+#F+
+#+G(/
)K%L
P$Q
6+#+G9
(
N
H
L
K%&&%
;(O
$%&()
*(()%+,/67")8"9,
::#
H
+#B
+#
+#+
J#I+
C#++
C#+
J#F+
J#FC
J#B+
#IC
#+
#C
(
J#I+
C#++
C#+
(
J#F+
J#FC
J#B+
(
#IC
#+
#C
+#C+K)
L
+#+
+#J+
+#C+
D
D
+#E+
D
D
N
+#+
D
$%&(
M D
!"#!
,,CRCR#+!!KS,LQ
+#C+!!,#+!!(R,
S&Q,
/QT8/"$L6
T/$9
AT42QT2100 [DATASHEET]
9554E–AT42–01/13
36
6.10.2 32-pin 7 x 7 mm TQFP
(
(
H
K%&&%
;(O
&%
;(O
+MWFM
L
%%$;($);%$)
6<?8@!!9
);(
;(O
$ #&Q?!*((?)+E,
K#
#!("8!"8#""H"
8+#C!!#!(!R!8!
"HSU!"8!"!!Q#
#L"S+#+!!!R!8!#
)K%L
;$
$%
A
D
D
#+
+#+C
D
+#C
+#IC
#++
#+C
B#FC
I#++
I#C
E#I+
F#++
F#+
(
B#FC
I#++
I#C
(
E#I+
F#++
F#+
H+#+
D
+#JC
+#+I
D
+#+
L
+#JC
D
+#FC
+#B+&
$%&(
$
$
!"#!
,"F#+RF#+R#+!!KS,+#B+!!
LQ,&Q?""T8/"
6&T/9
<&
AT42QT2100 [DATASHEET]
9554E–AT42–01/13
37
6.11
Part Marking
6.11.1 32-pin 5 x 5 mm MLF
Either part marking may be used. They are functionally identical.
32
Pin 1 ID
1
Abbreviated
part number
Please use this
marking to obscure
any reference to
ATtiny88 (or similar).
Atmel and lot
marking are
acceptable to remain
visible (Bar position
may be altered to
match existing
markings)
Date Code
Code revision
1.1, Released
Date Code Description
W=Week code
W week code number 1-52 where:
A=1 B=2 .... Z=26
then using the underscore A=27...Z=52
32
Pin 1 ID
1
Code revision
1.1, Released
Shortened
part number
LINE 4:
ATMEL LOTCODE
TRACEABILITY
(Variable field)
AT42QT2100 [DATASHEET]
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6.11.2 32-pin 7 x 7 mm TQFP
Either part marking may be used. They are functionally identical
32
Pin 1 ID
1
QT2100
AU 1R1
Shortened
Part Number
Code
Revision 1.1,
Release
Date Code
Date Code Description
YWW= Date programmed
WW week code number 1-52
Y year code letter 1-26 where: A=2001...J=2010 ...Z=2026
.
32
Pin 1 ID
1
Shortened
Part Number
Lot Number
(Variable Text)
ATMEL
QT2100
AU 1R1
LOTCODE
Code
Revision 1.1
Released
AT42QT2100 [DATASHEET]
9554E–AT42–01/13
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6.12
Part Numbers
Part Number
Description
AT42QT2100-MU
32-pin 5 × 5 mm MLF RoHS compliant IC
AT42QT2100-MUR
32-pin 5 × 5 mm MLF RoHS compliant IC
AT42QT2100-AU
32-pin 7 × 7 mm TQFP RoHS compliant IC
AT42QT2100-AUR
32-pin 7 × 7 mm TQFP RoHS compliant IC
The part number comprises:
AT = Atmel
42 = Touch Business Unit
QT = Charge-transfer technology
2100= (2) Slider/Wheel (10) number of channels (0) variant number
AU = TQFP chip
MU = MLF chip
R = Tape and reel
6.13
Moisture Sensitivity Level (MSL)
MSL Rating
Peak Body Temperature
Specifications
MSL3
260oC
IPC/JEDEC J-STD-020
AT42QT2100 [DATASHEET]
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Appendix A.
A.1
Migrating From QT1106 to QT2100
Introduction
The QT2100 is a replacement for the QT1106. As such, it is host-compatible with the QT1106 allowing existing
applications to be switched over without any changes to the host firmware.
Some changes to the application circuit will, however, be required and these are documented in this appendix.
A.2
Pin Configuration
The QT2100 has a different pin-out to the QT1106 (see Table A-1).
Table A-1.
Pin
Pin Compatibility
QT2100 Name
QT1106 Compatibility
1
SNSKB
SNSB
2
SNSB3
3
SNSKB
SNSB
4
VDD
QT1106 range is +2.8 V to +5.0 V
5
VSS
6
SNSKB
7
SNSB4
8
SNSB5
9
SNSKB
SNSB
10
SNSKB
SNSB
11
SNSKB
SNSB
12
SNSB6
13
SNSB7
14
SS
15
MOSI
16
MISO
17
SCK
18
VDD
QT1106 range is +2.8 V to +5.0 V
19
DRDY
Optional use on QT2100
20
CHANGE
21
VSS
22
SPREAD
23
SNSA1
24
SNSKA
25
SNSA2
SNSB
External oscillator circuit not required for QT2100
SNSA
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Table A-1.
A.3
Pin Compatibility (Continued)
Pin
QT2100 Name
QT1106 Compatibility
26
SNSKA
SNSA
27
SNSA3
28
SNSKA
29
RESET
30
SNSB1
31
SNSKB
32
SNSB2
SNSA
SNSB
Spread Spectrum Implementation
A SPREAD pin is provided which may be tied to Vdd or Ground via a resistor to enable/disable spread-spectrum
operation.
A.4
Component Retuning
In general it is expected that unchanged sense components will show little difference with the QT2100 for the same
sensor electrodes as the QT1106, but there may be cases where performance is improved by retuning component
values of Cs and Rs to the application circuit.
A.5
Components
An external oscillator is not required for QT2100.
A.6
Proximity
On the QT2100 any of the keys can be configured as proximity sensors but see Section 4.3.6 on page 15 for the
exception to this.
AT42QT2100 [DATASHEET]
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Associated Documents
For additional information, refer to the following document (downloadable from the Touch Technology area of the
Atmel website, www.atmel.com):

QTAN0079 Buttons, Sliders and Wheels Sensor Design Guide

Atmel AVR3000: QTouch Conducted Immunity Application Note

QTAN0087 Proximity Design Guide
Revision History
Revision No.
History
Revision AX – March 2011
Initial release for chip revision 0.6 – Preliminary
Revision BX – March 2011
Updated for chip revision 1.0
Revision CX – November 2011
Updated for chip revision 1.1 – Released
Revision D – November 2012
General update
Revision E – January 2013
Applied new template
AT42QT2100 [DATASHEET]
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