AT42QT1012 - Complete

Atmel AT42QT1012
One-channel Toggle-mode QTouch® Touch Sensor IC
with Power Management Functions
DATASHEET
Features
 Number of Keys:

One, toggle mode (touch-on / touch-off), plus programmable auto-off delay
and external cancel
 Configurable as either a single key or a proximity sensor
 Technology:

Patented spread-s
6 mm x 6 mm or larger (panel thickness dependent); widely different sizes and
shapes possible
 Electrode design:

Solid or ring electrode shapes
 PCB Layers required:

One
 Electrode materials:

Etched copper, silver, carbon, Indium Tin Oxide (ITO)
 Electrode substrates:

PCB, FPCB, plastic films, glass
 Panel materials:

Plastic, glass, composites, painted surfaces (low particle density metallic
paints possible)
 Panel thickness:

Up to 12 mm glass, 6 mm plastic (electrode size and Cs dependent)
 Key sensitivity:
 Settable via external capacitor (Cs)
 Interface:

Digital output, active high or active low (hardware configurable)
 Moisture tolerance:

Increased moisture tolerance based on hardware design and firmware tuning
 Power:

1.8 V – 5.5 V; 32 µA at 1.8 V
 Package:


6-pin SOT23-6 (3 x 3 mm) RoHS compliant
8-pin UDFN/USON (2 x 2 mm) RoHS compliant
 Signal processing:

Self-calibration, auto drift compensation, noise filtering
9543E–AT42–05/2013
Pinout and Schematic
1.1
Pinout Configurations
1.1.1
6-pin SOT23-6
1.1.2
OUT
1
VSS
2
SNSK
3
QT1012
1.
6
TIME
5
VDD
4
SNS
8-pin UDFN/USON
Pin 1 ID
8
SNS
7
VDD
3
6
TIME
4
5
OUT
SNSK
1
N/C
2
N/C
VSS
QT1012
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
2
1.2
Pin Descriptions
Table 1-1.
Pin Listing
If Unused,
Connect To...
6-Pin
8-Pin
Name
Type
Description
1
5
OUT
O (1)
2
4
VSS
P
3
1
SNSK
I/O
Sense pin. To Cs capacitor and to sense electrode
Cs + key
4
8
SNS
I/O
Sense pin. To Cs capacitor and multiplier configuration
resistor (Rm). Rm must be fitted and connected to either
VSS or VDD. See Section 3.11.4 on page 13 for details.
Cs
5
7
VDD
P
Power
6
6
TIME
I
Timeout configuration pin. Must be connected to either
VSS, VDD, OUT or an RC network. See Section 3.11 on
page 11 for details.
–
2
N/C
–
Not connected
Do not connect
–
3
N/C
–
Not connected
Do not connect
Output state. To switched circuit and output polarity
selection resistor (Rop)
Ground
1. I/O briefly on power-up
I
Input only
O
Output only, push-pull
I/O
Input/output
P
Ground or power
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
3
1.3
Schematics
1.3.1
6-pin SOT23-6
Figure 1-1. Basic Circuit Configuration
(active high output, toggle on/off, no auto switch off)
Note: bypass capacitor to be tightly
wired between VDD and VSS and
kept close to pin 5.
VDD
SENSE
ELECTRODE
Cby
5
VDD
Rs
3
OUT 1
SNSK
Cs
4
SNS
Rop
Rm
TIME 6
VSS
2
1.3.2
8-pin UDFN/USON
Figure 1-2. Basic Circuit Configuration
(active high output, toggle on/off, no auto switch off)
SENSE
ELECTRODE
Note: bypass capacitor to be tightly
wired between VDD and VSS and
kept close to pin 7.
VDD
Cby
7
VDD
Rs
1
OUT 5
SNSK
Cs
8
SNS
Rop
2
Rm
3
N/C
TIME 6
N/C
VSS
4
For component values in Figure 1-1 and Figure 1-2, check the following sections:

Cs capacitor (Cs) – see Section 4.2 on page 20

Sample resistor (Rs) – see Section 4.3 on page 20

Voltage levels – see Section 4.4 on page 20

Output polarity selection resistor (Rop) – see Section 3.9 on page 10

Rm resistor – see Section 3.11.2 on page 11

Bypass capacitor (Cby) – see page 20
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
4
2.
Overview of the AT42QT1012
2.1
Introduction
The AT42QT1012 (QT1012) is a single key device featuring a touch on/touch off (toggle) output with a
programmable auto switch-off capability.
The QT1012 is a digital burst mode charge-transfer (QT™) sensor designed specifically for touch controls. It includes
all hardware and signal processing functions necessary to provide stable sensing under a wide variety of changing
conditions; only low cost, noncritical components are required for operation. With its tiny low-cost packages, this
device can suit almost any product needing a power switch or other toggle-mode controlled function, especially
power control of small appliances and battery-operated products.
A unique “green” feature of the QT1012 is the timeout function, which can turn off power after a time delay.
Like all QTouch® devices, the QT1012 features automatic self-calibration, drift compensation, and spread-spectrum
burst modulation in order to provide for the most reliable touch sensing possible.
2.2
Basic Operation
Figure 1-1 on page 4 and Figure 1-2 on page 4 show basic circuits for the 6-pin and 8-pin devices.
The QT1012 employs bursts of charge-transfer cycles to acquire its signal. Burst mode permits power consumption
in the microamp range, dramatically reduces RF emissions, lowers susceptibility to EMI, and yet permits excellent
response time. Internally the signals are digitally processed to reject impulse noise, using a “consensus” filter which
requires four consecutive confirmations of a detection before the output is activated.
The QT switches and charge measurement hardware functions are all internal to the QT1012.
2.3
Electrode Drive
Figure 2-1 on page 6 shows the sense electrode connections (SNS, SNSK) for the QT1012.
For optimum noise immunity, the electrode should only be connected to the SNSK pin.
In all cases the sample capacitor Cs should be much larger than the load capacitance (Cx). Typical values for Cx are
5 – 20 pF while Cs is usually 2.2 – 50 nF.
Note:
Cx is not a physical discrete component on the PCB, it is the capacitance of the touch electrode and wiring.
It is show in Figure 2-1 on page 6 to aid understanding of the equivalent circuit.
Increasing amounts of Cx decrease gain, therefore it is important to limit the amount of load capacitance on both
SNS terminals. This can be done, for example, by minimizing trace lengths and widths and keeping these traces
away from power or ground traces or copper pours.
The traces, and any components associated with SNS and SNSK, will become touch sensitive and should be treated
with caution to limit the touch area to the desired location.
To endure that the correct output mode is selected at power-up, the OUT trace should also be carefully routed.
A series resistor, Rs, should be placed in line with SNSK to the electrode to suppress electrostatic discharge (ESD)
and electromagnetic compatibility (EMC) effects.
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
5
Figure 2-1. Sense Connections
VDD
SENSE
ELECTRODE
Cby
5
VDD
Rs
3
OUT 1
SNSK
Cs
4
SNS
Cx
TIME 6
VSS
2
2.4
Sensitivity
2.4.1
Introduction
The sensitivity on the QT1012 is a function of things like the value of Cs, electrode size and capacitance, electrode
shape and orientation, the composition and aspect of the object to be sensed, the thickness and composition of any
overlaying panel material, and the degree of ground coupling of both sensor and object.
2.4.2
Increasing Sensitivity
In some cases it may be desirable to increase sensitivity; for example, when using the sensor with very thick panels
having a low dielectric constant, or when the device is used as a proximity sensor. Sensitivity can often be increased
by using a larger electrode or reducing panel thickness. Increasing electrode size can have diminishing returns, as
high values of Cx will reduce sensor gain.
The value of Cs also has a dramatic effect on sensitivity, and this can be increased in value with the trade-off of a
slower response time and more power. Increasing the electrode's surface area will not substantially increase touch
sensitivity if its diameter is already much larger in surface area than the object being detected. Panel material can
also be changed to one having a higher dielectric constant, which will better help to propagate the field.
Ground planes around and under the electrode and its SNSK trace will cause high Cx loading and decrease gain.
The possible signal-to-noise ratio benefits of ground area are more than negated by the decreased gain from the
circuit, and so ground areas around electrodes are discouraged. Metal areas near the electrode will reduce the field
strength and increase Cx loading and should be avoided, if possible. Keep ground away from the electrodes and
traces.
2.4.3
Decreasing Sensitivity
In some cases the QT1012 may be too sensitive. In this case gain can easily be lowered further by decreasing Cs.
2.5
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).
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
6
3.
Operation Specifics
3.1
Acquisition Modes
3.1.1
Introduction
The OUT pin of the QT1012 can be configured to be active high or active low.


3.1.2
If active high then:

“on” is high

“off” is low
If active low then:

“on” is low

“off” is high
OUT Pin
The QT1012 runs in Low Power (LP) mode. In this mode it sleeps for approximately 80 ms at the end of each burst,
saving power but slowing response. On detecting a possible key touch, it temporarily switches to fast mode until
either the key touch is confirmed or found to be spurious (via the detect integration process).

If the touch is confirmed, the OUT pin is toggled and the QT1012 returns to LP mode (see Figure 3-1).

If the touch is not valid then the chip returns to LP mode but the OUT pin remains unchanged (see Figure 3-2).
~80 ms
SNSK
sleep
Key
touch
Figure 3-1. Low Power Mode: Touch Confirmed (Output in Off Condition)
fast detect
integrator
sleep
OUT
SNSK
~80 ms
Key
touch
Figure 3-2. Low Power Mode: Touch Denied (Output in Off Condition)
Sleep
Sleep
Fast detect
integrator
Sleep
Sleep
OUT
3.2
Detect Threshold
The device detects a touch when the signal has crossed a threshold level. The threshold level is fixed at 10 counts.
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
7
3.3
Detect Integrator
It is desirable to suppress detections generated by electrical noise or from quick brushes with an object. To
accomplish this, the QT1012 incorporates a detect integration (DI) counter that increments with each detection until
a limit is reached, after which the output is activated. If no detection is sensed prior to the final count, the counter is
reset immediately to zero. In the QT1012, the required count is four.
The DI can also be viewed as a “consensus filter” that requires four successive detections to create an output.
3.4
Recalibration Timeout
If an object or material obstructs the sense electrode the signal may rise enough to create a detection, preventing
further operation. To stop this, the sensor includes a timer which monitors detections. If a detection exceeds the
timer setting, the sensor performs a full recalibration. This does not toggle the output state but ensures that the
QT1012 will detect a new touch correctly. The timer is set to activate this feature after ~60 s. This will vary slightly
with Cs.
3.5
Forced Sensor Recalibration
The QT1012 has no recalibration pin; a forced recalibration is accomplished when the device is powered up or after
the recalibration timeout. However, supply drain is low so it is a simple matter to treat the entire IC as a controllable
load; driving the QT1012 VDD pin directly from another logic gate or a microcontroller port will serve as both power
and “forced recalibration”. The source resistance of most CMOS gates and microcontrollers is low enough to provide
direct power without a problem.
3.6
Drift Compensation
Signal drift can occur because of changes in Cx and Cs over time. It is crucial that drift be compensated for,
otherwise false detections, nondetections, and sensitivity shifts will follow.
Drift compensation (Figure 3-3) is performed by making the reference level track the raw signal at a slow rate, but
only while there is no detection in effect. The rate of adjustment must be performed slowly, otherwise legitimate
detections could be ignored. The QT1012 drift compensates using a slew-rate limited change to the reference level;
the threshold and hysteresis values are slaved to this reference.
Once an object is sensed, the drift compensation mechanism ceases since the signal is legitimately high, and
therefore should not cause the reference level to change.
Figure 3-3. Drift Compensation
Signal
Hysteresis
Threshold
Reference
Output
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
8
The QT1012 drift compensation is asymmetric; the reference level drift-compensates in one direction faster than it
does in the other. Specifically, it compensates faster for decreasing signals than for increasing signals. Increasing
signals should not be compensated for quickly, since an approaching finger could be compensated for partially or
entirely before even approaching the sense electrode. However, an obstruction over the sense pad, for which the
sensor has already made full allowance, could suddenly be removed leaving the sensor with an artificially elevated
reference level and thus become insensitive to touch. In this latter case, the sensor will compensate for the object's
removal very quickly.
With large values of Cs and small values of Cx, drift compensation will appear to operate more slowly than with the
converse. Note that the positive and negative drift compensation rates are different.
3.7
Response Time
The QT1012 response time is highly dependent on the run mode and burst length, which in turn is dependent on Cs
and Cx. With increasing Cs, response time slows, while increasing levels of Cx reduce response time.
3.8
Spread Spectrum
The QT1012 modulates its internal oscillator by ±7.5% during the measurement burst. This spreads the generated
noise over a wider band, reducing emission levels. This also reduces susceptibility since there is no longer a single
fundamental burst frequency.
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
9
3.9
Output Polarity Selection
The output (OUT pin) of the QT1012 can be configured to have an active high or active low output by means of the
output configuration resistor Rop. The resistor is connected between the output and either Vss or Vdd (see Figure 34 and Table 3-1). A typical value for Rop is 100 k.
Figure 3-4. Output Polarity (6-pin SOT23)
SENSE
ELECTRODE
VDD
Cby
100 nF
5
Rs
VDD
Rop
3 SNSK
Vop
Cs
4 SNS
OUT
Rm
1
TIME 6
VSS
2
Table 3-1.
Note:
Output Configuration
Name (Vop)
Function (Output Polarity)
Vss
Active high
Vdd
Active low
Some devices, such as Digital Transistors, have an internal biasing network that will naturally pull the OUT
pin to its inactive state. If these are being used then the resistor Rop is not required (see Figure 3-5).
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
10
Figure 3-5. Output Connected to Digital Transistor (6-pin SOT23)
SENSE
ELECTRODE
VDD
Cby
100 nF
5
Rs
VDD
Load
3 SNSK
Cs
4 SNS
OUT
1
TIME 6
Rm
VSS
2
3.10
Output Drive
The OUT pin can sink or source up to 2 mA. When a large value of Cs (>20 nF) is used the OUT current should be
limited to <1 mA to prevent gain-shifting side effects, which happen when the load current creates voltage drops on
the die and bonding wires; these small shifts can materially influence the signal level to cause detection instability.
3.11
Auto-Off Delay
3.11.1 Introduction
In addition to toggling the output on/off with a key touch, the QT1012 can automatically switch the output off after a
time, typically ±10 percent of the nominal stated time. This feature can be used to save power in situations where the
switched device could be left on inadvertently.
The QT1012 has:

three predefined delay times (Section 3.11.2)

the ability to set a user-programmed delay (Section 3.11.3 on page 13)

the ability to override the auto-off delay (Section 3.11.5 on page 17)
The TIME and SNS pins are used to configure the Auto-off delay and must always be connected in one of the ways
described in Section 3.11.2.
3.11.2 Auto-off – Predefined Delay
To configure the predefined delay the TIME pin is hard wired to Vss, Vdd or OUT as shown in Table 3-2 on page 12
and Table 3-3 on page 12. This provides nominal values of 15 minutes, 60 minutes or infinity (remains on until
toggled off).
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
11
A single 1 M resistor (Rm) is connected between the SNS pin and the logic level Vm to provide three auto-off
functions: delay multiplication, delay override and delay retriggering. On power-up the logic level at Vm is assessed
and the delay multiplication factor is set to x1 or x24 accordingly (see Figure 3-6 on page 12, Table 3-2 on page 12
and Table 3-3 on page 12). At the end of each acquisition cycle the logic level of Vm is monitored to see if an Autooff delay override is required (see Section 3.11.5 on page 17).
Setting the delay multiplier to x24 will decrease the key sensitivity. To compensate, it may be necessary to increase
the value of Cs.
Figure 3-6. Predefined Delay
SENSE
ELECTRODE
VDD
Cby
100 nF
5
Rs
VDD
3 SNSK
Cs
4 SNS
Rm
OUT
1
TIME 6 Vt
VSS
Rop
2
Vm
Table 3-2.
Vt
Predefined Auto-off Delay (Active High Output)
Auto-off Delay (to)
Vss
Infinity (remain on until toggled to off)
Vdd
15 minutes
OUT
60 minutes
Table 3-3.
Vt
Predefined Auto-off Delay (Active Low Output)
Auto-off Delay (to)
Vss
15 minutes
Vdd
Infinity (remain on until toggled to off)
OUT
60 minutes
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
12
Table 3-4.
Auto-off Delay Multiplier
Vm
Auto-off Delay Multiplier
Vss
to × 1
Vdd
to × 24
3.11.3 Auto-off – User-programmed Delay
If a user-programmed delay is required, a RC network (resistor and capacitor) can be used to set the auto-off delay
(see Table 3-5 on page 14 and Figure 3-7 on page 13). The delay time is dependent on the RC time constant
(Rt × Ct), the output polarity and the supply voltage. Section 3.11.4 on page 13 gives full details of how to configure
the QT1012 to have auto-off delay times ranging from minutes to hours.
Figure 3-7. Programmable Delay
SENSE
ELECTRODE
VDD
Cby
100 nF
5
Rs
VDD
3 SNSK
Cs
4 SNS
OUT
1
Rop
Rm
TIME
6
VSS
Cs
2
Rop
Vm
3.11.4 Configuring the User-programmed Auto-off Delay
The QT1012 can be configured to give auto-off delays ranging from minutes to hours by means of a simple RC
network and the delay multiplier input.
With the delay multiplier set at x1 the auto-off delay is calculated as follows:
Rt  Ct
Delay value = integer value of ------------------ x 15 seconds
K
Delay  K
and Rt × Ct = -------------------------15
Note:
Rt is in k, Ct is in nF, Delay is in seconds. K values are obtained from Figure 3-8 on page 14.
Rt  Ct
To ensure correct operation it is recommended that the value of ------------------ is between 4 and 240.
K
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
13
Values outside this range may be interpreted as the hard wired options TIME linked to OUT and TIME linked to “off”
respectively, causing the QT1012 to use the relevant predefined auto-off delays.
Table 3-5.
Programmable Auto-off Delay (Example)
Vm = Vss (delay multiplier = 1), Vdd = 3.5 V
Output Type
Auto-off Delay (Seconds)
Active high
(Rt × Ct × 15) / 19
Active low
(Rt × Ct × 15) / 22
K values (19 and 22) are obtained from Figure 3-8 on page 14.
Note:
Rt is in k, Ct is in nF.
Figure 3-8. Typical Values of K Versus Supply Voltage
The charts in Figure 3-8 show typical values of K versus supply voltage for a QT1012 with active high or active low
output.
Example using the formula to calculate Rt and Ct
Requirements:

Active high output (Vop connected to VSS)

Auto-off delay nominal 45 minutes

VDD = 3.5 V
Proceed as follows:
1.
Calculate Auto-off delay in seconds 45 x 60 = 2700
2.
Obtain K from Figure 3-8, K = 22.8
3.
2700  22.8
Calculate Rt × Ct = ---------------------------- = 4104
4.
Decide on a value for Rt or Ct (for example, Ct = 47 nF)
5.
4104
Calculate Rt = ------------ = 87 k
6.
RtxCt
Verify that --------------- = 179 (which is between 4 and 240)
15
47
K
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
14
As an alternative to calculation, Figure 3-9 and Figure 3-10 on page 16 show charts of typical curves of auto-off
delay against resistor and capacitor values for active high and active low outputs at various values of VDD (delay
multiplier = x1).
Figure 3-9. Auto-off Delay, Active High Output
Vm = Vss (delay multiplier = x1)
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
15
Figure 3-10. Auto-off Delay, Active Low Output
Vm = Vss (delay multiplier = x1)
Example using a chart to calculate Rt and Ct
Requirements:

Active low output (Vop connected to VSS)

Auto-off delay 25 minutes

VDD = 4 V
1.
Calculate Auto-off delay in seconds 25 × 60 = 1500.
2.
Find
3.
This shows the following suitable Ct / Rt combinations:
1500
------------ = 1500 on the 4 V chart in Figure 3-10.
1

100 nF / 20 k

47 nF / 40 k

22 nF / 90 k

10 nF / 190 k
Note:
The Auto-off delay times shown are nominal and will vary from chip to chip and with capacitor and
resistor tolerance.
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
16
3.11.5 Auto-off – Overriding the Auto-off Delay
In normal operation the QT1012 output is turned off automatically after the auto-off delay. In some applications it
may be useful to extend the auto-off delay (“sustain” function) or to switch the output off immediately (“cancel”
function). This can be achieved by pulsing the voltage on the delay multiplier resistor Rm as shown in Figure 3-11
and Figure 3-12 on page 18.
To ensure the pulse is detected it must be present for typical times as shown in Table 3-6.
Table 3-6.
Time Delay Pulse
Pulse Duration
Action
tp – series of short pulses, typically 65 ms
“Sustain”/retrigger (reload auto-off delay counter)
tp – long pulse, typically 250 ms
“Cancel”/switch output to off state and inhibit further
touch detection until Vm returns to original state
While Vm is held in the override state the QT1012 inhibits bursts and waits for Vm to return to its original state. When
Vm returns to its original state the QT1012 performs a sensor recalibration before continuing in its current output
state.
Figure 3-11. Override Pulse (Delay Multiplier x1)
SENSE
ELECTRODE
VDD
Cby
100 nF
5
Rs
VDD
3 SNSK
Cs
4 SNS
Rm
OUT
1
TIME 6
VSS
Rop
2
Vm
Vdd
Vss
Tp
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
17
Figure 3-12. Override Pulse (Delay Multiplier x24)
SENSE
ELECTRODE
VDD
Cby
100 nF
5
Rs
VDD
3 SNSK
Cs
4 SNS
OUT
1
TIME 6
Rm
VSS
Rop
2
Vm
Vdd
Vss
Tp
Figure 3-13 shows override pulses being applied to a QT1012 with delay multiplier set to x1.
Figure 3-13. Overriding Auto-off
O
OUT
P
P
P
toff
Vm
Bursts
SNSK
C
C
C
C
P - override (reload auto off delay)
O - switch output off (toff burst time + 50ms)
C - sensor recalibration
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
18
3.12
Examples of Typical Applications
Figure 3-14. Application 1:
Active low, driving PNP transistor, auto-off time 375 s x 24 = 9000 s = 2.5 hours
+3V
100nF
Rm
1M
SENSE
ELECTRODE
DTA143
5
VDD
RS
3
OUT 1
SNSK
CS
4
Rt
SNS
10k
TIME 6
2.2k
Ct
VSS
Load
47nF
2
Auto-off time obtained from 3 V chart in Figure 3-10 on page 16
Figure 3-15. Application 2:
Active high, driving high impedance, auto-off time 315 s x 1 = 5.25 minutes
+5V
100nF
SENSE
ELECTRODE
5
VDD
Rs
3
OUT 1
SNSK
CS
4
Rt
SNS
10k
TIME 6
Rm
1M
VSS
Rop
Ct
100k
47nF
2
Auto-off time obtained from 5 V chart in Figure 3-9 on page 15
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
19
4.
Circuit Guidelines
4.1
More Information
Refer to Application Note QTAN0002, Secrets of a Successful QTouch Design and the Touch Sensors Design Guide
(both downloadable from the Atmel website), for more information on construction and design methods.
4.2
Sample Capacitor
Cs is the charge sensing sample capacitor. The required Cs value depends on the thickness of the panel and its
dielectric constant. Thicker panels require larger values of Cs. Typical values are 2.2 nF to 50 nF depending on the
sensitivity required; larger values of Cs demand higher stability and better dielectric to ensure reliable sensing.
The Cs capacitor should be a stable type, such as X7R ceramic or PPS film. For more consistent sensing from unit
to unit, 5% tolerance capacitors are recommended. X7R ceramic types can be obtained in 5% tolerance at little or no
extra cost. In applications where high sensitivity (long burst length) is required the use of PPS capacitors is
recommended.
For battery powered operation a higher value sample capacitor may be required.
4.3
Rs Resistor
Series resistor Rs is in line with the electrode connection and should be used to limit ESD currents and to suppress
radio frequency interference (RFI). It should be approximately 4.7 k to 33 k.
Although this resistor may be omitted, the device may become susceptible to external noise or RFI. See Application
Note QTAN0002, Secrets of a Successful QTouch Design, for details of how to select these resistors.
4.4
Power Supply and PCB Layout
See Section 5.2 on page 22 for the power supply range.
If the power supply is shared with another electronic system, care should be taken to ensure that the supply is free of
digital spikes, sags, and surges which can adversely affect the QT1012. The QT1012 will track slow changes in Vdd,
but it can be badly affected by rapid voltage fluctuations. It is highly recommended that a separate voltage regulator
be used just for the QT1012 to isolate it from power supply shifts caused by other components.
If desired, the supply can be regulated using a Low Dropout (LDO) regulator, although such regulators often have
poor transient line and load stability. See Application Note QTAN0002, Secrets of a Successful QTouch Design, for
further information on power supply considerations.
Parts placement: The chip should be placed to minimize the SNSK trace length to reduce low frequency pickup,
and to reduce stray Cx which degrades gain. The Cs and Rs resistors (see Figure 1-1 on page 4) should be placed
as close to the body of the chip as possible so that the trace between Rs and the SNSK pin is very short, thereby
reducing the antenna-like ability of this trace to pick up high frequency signals and feed them directly into the chip. A
ground plane can be used under the chip and the associated discrete components, but the trace from the Rs resistor
and the electrode should not run near ground, to reduce loading.
For best EMC performance the circuit should be made entirely with SMT components.
Electrode trace routing: Keep the electrode trace (and the electrode itself) away from other signal, power, and
ground traces including over or next to ground planes. Adjacent switching signals can induce noise onto the sensing
signal; any adjacent trace or ground plane next to, or under, the electrode trace will cause an increase in Cx load and
desensitize the device.
Bypass Capacitor: Important – For proper operation a 100 nF (0.1 µF) ceramic bypass capacitor must be used
directly between Vdd and Vss, to prevent latch-up if there are substantial Vdd transients; for example, during an ESD
event. The bypass capacitor should be placed very close to the VSS and VDD pins.
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
20
4.5
Power On
On initial power up, the QT1012 requires approximately 250 ms to power on to allow power supplies to stabilize.
During this time the OUT pin state is not valid and should be ignored.
Note that recalibration takes approximately 200 ms, so the QT1012 takes approximately 450 ms in total from initial
power on to become active.
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
21
5. Specifications
5.1
Absolute Maximum Specifications
Operating temperature
–40°C to +85°C
Storage temperature
–55°C to +125°C
VDD
0 to +6.5 V
Max continuous pin current, any control or drive pin
±20 mA
Short circuit duration to Vss, any pin
Infinite
Short circuit duration to Vdd, any pin
Infinite
Voltage forced onto any pin
–0.6 V to (Vdd + 0.6) 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
5.2
Recommended Operating Conditions
VDD
+1.8 to +5.5 V
Short-term supply ripple + noise
±20 mV
Long-term supply stability
±100 mV
Cs value
2.2 to 50 nF
Cx value
5 to 20 pF
5.3
AC Specifications
Vdd = 3.0V, Cs = 10 nF, Cx = 5 pF, Ta = recommended range, unless otherwise noted
Parameter
Description
Min
Typ
Max
Units
Notes
TRC
Recalibration time
–
200
–
ms
Cs, Cx dependent
TPC
Charge duration
–
3
–
µs
±7.5% spread spectrum variation
TPT
Transfer duration
–
6
–
µs
±7.5% spread spectrum variation
TG1
Time between end of burst and
start of the next (Fast mode)
–
2.6
–
ms
TG2
Time between end of burst and
start of the next (LP mode)
–
80
–
ms
Increases with decreasing VDD
TBL
Burst length
–
1.86
–
ms
VDD, Cs and Cx dependent. See
Section 4.2 for capacitor
selection.
TR
Response time
–
–
100
ms
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
22
5.4
Signal Processing
Vdd = 3.0V, Cs = 10 nF, Cx = 5 pF, Ta = recommended range, unless otherwise noted
Description
Min
Typ
Max
Units
Threshold differential
10
counts
Hysteresis
2
counts
Consensus filter length
4
samples
5.5
Notes
DC Specifications
Vdd = 3.0V, Cs = 4.7 nF, Cx = 5 pF, short charge pulse, Ta = recommended range, unless otherwise noted
Parameter
VDD
IDD
Description
Supply voltage
Supply current
Min
Typ
1.8
Max
Units
5.5
V
Notes
–
32
36
59
88
124
–
µA
1.8 V
2.0 V
3.0 V
4.0 V
5.0 V
Required for proper start-up
VDDS
Supply turn-on slope
100
–
–
V/s
VIL
Low input logic level
–
–
0.2 × Vdd
0.3 × Vdd
V
Vdd = 1.8 V – 2.4 V
Vdd = 2.4 V – 5.5 V
VHL
High input logic level
0.7 × Vdd
0.6 × Vdd
–
V
Vdd = 1.8 V – 2.4 V
Vdd = 2.4 V – 5.5 V
VOL
Low output voltage
–
–
0.6
V
OUT, 4 mA sink
VOH
High output voltage
Vdd – 0.7
–
–
V
OUT, 1 mA source
IIL
Input leakage current
–
–
±1
µA
CX
Load capacitance range
0
–
100
pF
AR
Acquisition resolution
–
9
14
bits
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
23
5.6
Mechanical Dimensions
5.6.1
6-pin SOT23
'
'
@
]H
'H$\G$'
<
>#> .
.
>#> 'H$\G$'
>#
*
.+
'H$\G$'
''.H'[
G
.
*))*$H)'$H*$
JL()9Q!!R
)H$
$*)
)A
W
W
#@
>
W
>#
>#X>
W
#
>
#->
#X>
#>>
B)*G
$ # %!"%&''(
)*+,-.#
# !"9!":"%;9
<9#)":"%;9<9%""
=>#!!#
# !<"9!<9#
""<"!<9%""9%"%
=%!=!9!<!<?!%>#>-!!
@# ((!(!#
'
#>
#->
#>>
'
#>
#>
#,
>#
>
>#@
>#
G
>#X
<
>#
>
W
>#>
>#>X
W
>#>
Y
>Z
W
-Z
$*'
!"#!
;+";#X>=#>!!"!""*9"
J*
R
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
24
5.6.2
8-pin UDFN/USON
_
-
,
_
!_
-
'
>#
'
H$H
G
@
@
I
>#> -A
G
<
>#> _
JL()9Q!!R
+
+
>#>
>#>>
+
>#>
$*'
#""!!!#"#
#"?"%=""%!"#
"?%""=>#>!!#
#[%""=>#>!!#
@#^(&'')*+
)*+#
<
>#>
+
>#
>
#X
#>>
#>
#@>
#>
#>
'
#X
#>>
#>
'
#>>
>#->
>#X>
>#>
G
>#>
>#
>
>#@>
>#>
+
+
>
!"#!
;-+;#>=#>=>#!!?;>#!!%;
>#X=#!!'=;L"+%9":"
$GJL:$L*$R
B\
-)@
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
25
5.7
Part Marking
5.7.1
AT42QT1012– 6-pin SOT23-6
Abbreviated
Part Number:
AT42QT
Pin 1 ID
5.7.2
AT42QT1012– 8-pin UDFN/USON
Abbreviated
Part Number:
AT42QT1012
Die Revision
(Example: “E” shown)
Class code
(H = Industrial,
green NiPdAu)
Assembly Location
Code
(Example: “C” shown)
Pin 1 ID
Lot Number Trace
code (Variable text)
Pin 1
5.8
Last Digit of Year
(Variable text)
Part Number
Part Number
Description
AT42QT1012-TSHR
6-pin SOT23 RoHS compliant IC
AT42QT1012-MAH
8-pin UDFN/USON RoHS compliant IC
The part number comprises:
AT = Atmel
42 = Touch Business Unit
QT = Charge-transfer technology
1012 = (1) keys, (01) number of keys, (2) variant number
TSH = SOT23 chip
MAH = UDFN/USON chip
R = Tape and reel
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
26
5.9
Moisture Sensitivity Level (MSL)
MSL Rating
MSL1
Peak Body Temperature
o
260 C
Specifications
IPC/JEDEC J-STD-020
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
27
Associated Documents

Application Note – QTAN0002, Secrets of a Successful QTouch Design

User Guide – Touch Sensors Design Guide
Revision History
Revision No.
History
Revision A – August 2009
Initial release for chip revision 2.4
Revision B – September 2009
Changes to Cs value.
Revision C – May 2010
Updated for chip revision 3.1
Revision D – August 2010
Updated for chip revision 3.3
Revision E – May 2013
General update
New template
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
28
Notes
AT42QT1012 [DATASHEET]
9543E–AT42–05/2013
29
Atmel Corporation
1600 Technology Drive
Atmel Asia Limited
Unit 01-5 & 16, 19F
Atmel München GmbH
Business Campus
Atmel Japan G.K.
16F Shin-Osaki Kangyo Bldg
San Jose, CA 95110
BEA Tower, Millennium City 5
Parkring 4
1-6-4 Osaki, Shinagawa-ku
USA
418 Kwun Tong Roa
D-85748 Garching bei München
Tokyo 141-0032
Tel: (+1) (408) 441-0311
Kwun Tong, Kowloon
GERMANY
JAPAN
Fax: (+1) (408) 487-2600
HONG KONG
Tel: (+49) 89-31970-0
Tel: (+81) (3) 6417-0300
www.atmel.com
Tel: (+852) 2245-6100
Fax: (+49) 89-3194621
Fax: (+81) (3) 6417-0370
Fax: (+852) 2722-1369
© 2013 Atmel Corporation. All rights reserved. / Rev.: 9543E–AT42–05/2013
Atmel®, Atmel logo and combinations thereof, QTouch® and others are registered trademarks or trademarks of Atmel Corporation or its subsidiaries. Other
terms and product names may be registered trademarks or trademarks of others.
Disclaimer: The information in this document is provided in connection with Atmel products. No license, express or implied, by estoppel or otherwise, to any intellectual property right is granted by this
document or in connection with the sale of Atmel products. EXCEPT AS SET FORTH IN THE ATMEL TERMS AND CONDITIONS OF SALES LOCATED ON THE ATMEL WEBSITE, ATMEL
ASSUMES NO LIABILITY WHATSOEVER AND DISCLAIMS ANY EXPRESS, IMPLIED OR STATUTORY WARRANTY RELATING TO ITS PRODUCTS INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL ATMEL BE LIABLE FOR ANY DIRECT, INDIRECT,
CONSEQUENTIAL, PUNITIVE, SPECIAL OR INCIDENTAL DAMAGES (INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS AND PROFITS, BUSINESS INTERRUPTION, OR LOSS OF
INFORMATION) ARISING OUT OF THE USE OR INABILITY TO USE THIS DOCUMENT, EVEN IF ATMEL HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. Atmel makes no
representations or warranties with respect to the accuracy or completeness of the contents of this document and reserves the right to make changes to specifications and products descriptions at any
time without notice. Atmel does not make any commitment to update the information contained herein. Unless specifically provided otherwise, Atmel products are not suitable for, and shall not be
used in, automotive applications. Atmel products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life.
Similar pages