AT42QT1012-MAHR - MICROCHIP TECHNOLOGY

AT42QT1012

AT42QT1012 Data Sheet

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 device is One-channel Toggle-mode QTouch® Touch

Sensor IC with Power Management Functions.

The QT1012 features a digital burst mode charge-transfer sensor designed specifically for touch controls

and a unique “green” feature - the timeout function, which can turn off power after a time delay.

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

AT42QT1012

Table of Contents

Introduction......................................................................................................................1

Features.......................................................................................................................... 1

1. Pinout and Schematic................................................................................................5

1.1. Pinout Configurations................................................................................................................... 5

1.2. Pin Descriptions........................................................................................................................... 5

1.3. Schematics...................................................................................................................................6

2. Overview of the AT42QT1012................................................................................... 7

2.1. Introduction...................................................................................................................................7

2.2. Basic Operation............................................................................................................................7

2.3. Electrode Drive.............................................................................................................................7

2.4. Sensitivity..................................................................................................................................... 8

2.5. Moisture Tolerance....................................................................................................................... 8

3. Operation Specifics................................................................................................. 10

3.1. Acquisition Modes...................................................................................................................... 10

3.2. Detect Threshold........................................................................................................................ 10

3.3. Detect Integrator.........................................................................................................................11

3.4. Recalibration Timeout.................................................................................................................11

3.5. Forced Sensor Recalibration...................................................................................................... 11

3.6. Drift Compensation.....................................................................................................................11

3.7. Response Time.......................................................................................................................... 12

3.8. Spread Spectrum....................................................................................................................... 12

3.9. Output Polarity Selection............................................................................................................12

3.10. Output Drive............................................................................................................................... 13

3.11. Auto-Off Delay............................................................................................................................13

3.12. Examples of Typical Applications...............................................................................................21

4. Circuit Guidelines.................................................................................................... 22

4.1. More Information........................................................................................................................ 22

4.2. Sample Capacitor.......................................................................................................................22

4.3. Rs Resistor.................................................................................................................................22

4.4. Power Supply and PCB Layout.................................................................................................. 22

4.5. Power On................................................................................................................................... 23

5. Specifications.......................................................................................................... 24

5.1. Absolute Maximum Specifications..............................................................................................24

5.2. Recommended Operating Conditions........................................................................................ 24

5.3. AC Specifications....................................................................................................................... 24

5.4. Signal Processing.......................................................................................................................25

5.5. DC Specifications....................................................................................................................... 25

5.6. Mechanical Dimensions............................................................................................................. 26

5.7. Part Marking............................................................................................................................... 28

5.8. Part Number............................................................................................................................... 28

5.9. Moisture Sensitivity Level (MSL)................................................................................................ 29

6. Associated Documents............................................................................................30

7. Revision History.......................................................................................................31

The Microchip Web Site................................................................................................ 32

Customer Change Notification Service..........................................................................32

Customer Support......................................................................................................... 32

Microchip Devices Code Protection Feature................................................................. 32

Legal Notice...................................................................................................................33

Trademarks................................................................................................................... 33

Quality Management System Certified by DNV.............................................................34

Worldwide Sales and Service........................................................................................35

AT42QT1012

1. Pinout and Schematic

1.1 Pinout Configurations

1.1.1 6-pin SOT23-6

VDD

TIME

SNSK

VSS

OUT

SNS

QT1012

1.1.2 8-pin UDFN/USON

Pin 1 ID

OUT

SNSK

VSS

SNS

VDD

TIME

N/C

1 8

QT1012

1.2 Pin Descriptions

Table 1-1. Pin Listing

6-Pin 8-Pin Name Type Description If Unused, Connect

To...

1 5 OUT O(1) Output state. To switched circuit and output polarity selection

resistor (Rop)

2 4 VSS P Ground

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 for details.

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 for details.

— 2 N/C — Not connected Do not connect

— 3 N/C — Not connected Do not connect

AT42QT1012

(1) I/O briefly on power-up

I Input only O Output only, push-pull

I/O Input/output P Ground or power

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)

VDD

TIME

VSS

OUT 1

Rop

VDD

SNSK

SNS

Note: bypass capacitor to be tightly

wired between VDD and VSS and

kept close to pin 5.

SENSE

ELECTRODE Cby

1.3.2 8-pin UDFN/USON

Figure 1-2. Basic Circuit Configuration

(active high output, toggle on/off, no auto switch off)

VDD

TIME

VSS

OUT 5

Rop

VDD

SNSK

SNS

Note: bypass capacitor to be tightly

wired between VDD and VSS and

kept close to pin 7.

SENSE

ELECTRODE Cby

Rm N/C

N/C

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

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 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 and Figure 1-2 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 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 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

Figure 2-1. Sense Connections

VDD

TIME

VSS

OUT 1

VDD

SNSK

SNS

SENSE

ELECTRODE

Cby

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

AT42QT1012

recommendations in the application note Atmel AVR3002: Moisture Tolerant QTouch Design

(downloadable from www.microchip.com).

AT42QT1012

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.

• If active high then:

– “on” is high

– “off” is low

• If active low then:

– “on” is low

– “off” is high

3.1.2 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

"Low Power Mode: Touch Confirmed" below).

• If the touch is not valid then the chip returns to LP mode but the OUT pin remains unchanged (see

figure "Low Power Mode: Touch Denied" below).

Figure 3-1. Low Power Mode: Touch Confirmed (Output in Off Condition)

SNSK sleep sleep

fast detect

integrator

OUT

Key

touch

~80 ms

Figure 3-2. Low Power Mode: Touch Denied (Output in Off Condition)

SNSK Sleep

Fast detect

integrator

Key

touch

~80 ms

Sleep Sleep

OUT

Sleep

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

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

Threshold

Signal Hysteresis

Reference

Output

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

AT42QT1012

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.

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 3-4 and Table 3-1). A typical value for Rop is 100 kΩ.

Figure 3-4. Output Polarity (6-pin SOT23)

VDD

OUT

VSS

VDD

Rop

3SNSK Vop

4SNS

SENSE

ELECTRODE

TIME 6

Cby

100 nF

AT42QT1012

Table 3-1. Output Configuration

Name (Vop) Function (Output Polarity)

Vss Active high

Vdd Active low

Note: 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).

Figure 3-5. Output Connected to Digital Transistor (6-pin SOT23)

Load

VDD

OUT

VSS

3SNSK

TIME 6

4SNS

SENSE

ELECTRODE

VDD

Cby

100 nF

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)

• the ability to override the auto-off delay (Section 3.11.5)

AT42QT1012

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

and Table 3-3. This provides nominal values of 15 minutes, 60 minutes or infinity (remains on until

toggled off).

A single 1 MΩ 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, Table

3-2 and Table 3-3). At the end of each acquisition cycle the logic level of Vm is monitored to see if an

Auto-off delay override is required (see Section 3.11.5).

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

VDD

OUT

VSS

4SNS

TIME 6Vt

3SNSK

SENSE

ELECTRODE

Rop

VDD

Cby

100 nF

Table 3-2. Predefined Auto-off Delay (Active High Output)

Vt Auto-off Delay (to)

Vss Infinity (remain on until toggled to off)

Vdd 15 minutes

OUT 60 minutes

AT42QT1012

Table 3-3. Predefined Auto-off Delay (Active Low Output)

Vt Auto-off Delay (to)

Vss 15 minutes

Vdd Infinity (remain on until toggled to off)

OUT 60 minutes

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 and Figure 3-7). The delay time is dependent on the RC time constant (Rt ×

Ct), the output polarity and the supply voltage. Section 3.11.4 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

VDD

OUT

VSS

4SNS

TIME 6

3SNSK

SENSE

ELECTRODE

Rop

VDD

Cby

100 nF

Rop

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:

Delay value = integer value of Rt × Ct

� x 15 seconds

AT42QT1012

and Rt × Ct = Delay × �

Note: Rt is in kΩ, Ct is in nF, Delay is in seconds. K values are obtained from Figure 3-8.

To ensure correct operation it is recommended that the value of Rt × Ct

� is between 4 and 240.

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.

Note: Rt is in kΩ, 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. Calculate Rt × Ct = 2700 × 22.8

15 = 4104

4. Decide on a value for Rt or Ct (for example, Ct = 47 nF)

5. Calculate Rt = 4104

47 = 87 k

6. Verify that RtxCt

� = 179 (which is between 4 and 240)

AT42QT1012

As an alternative to calculation, Figure 3-9 and Figure 3-10 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

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 1500

1 = 1500 on the 4 V chart in Figure 3-10.

3. This shows the following suitable Ct / Rt combinations:

– 100 nF / 20 kΩ

– 47 nF / 40 kΩ

– 22 nF / 90 kΩ

– 10 nF / 190 kΩ

Note: The Auto-off delay times shown are nominal and will vary from chip to chip and with

capacitor and resistor tolerance.

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.

AT42QT1012

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)

VDD

OUT

VSS

4SNS

TIME 6

3SNSK

SENSE

ELECTRODE

Rop

VDD

Cby

100 nF

Vdd

Vss

AT42QT1012

Figure 3-12. Override Pulse (Delay Multiplier x24)

VDD

OUT

VSS

4SNS

TIME 6

3SNSK

SENSE

ELECTRODE

Rop

VDD

Cby

100 nF

Vdd

Vss

Figure 3-13 shows override pulses being applied to a QT1012 with delay multiplier set to x1.

Figure 3-13. Overriding Auto-off

SNSK

toff

C C C

OUT

P P P

P - override (reload auto off delay)

O - switch output off (t burst time + 50ms)

C - sensor recalibration

off

Bursts

AT42QT1012

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

Auto-off time obtained from 3 V chart in Figure 3-10 on page 16

Load

VDD

TIME

VSS

OUT 1

10k

+3V

SNSK

SNS

SENSE

ELECTRODE

100nF

47nF

2.2k

DTA143

Auto-off time obtained from 3 V chart in Figure 3-10

Figure 3-15. Application 2:

Active high, driving high impedance, auto-off time 315 s x 1 = 5.25 minutes

Auto-off time obtained from 5 V chart in Figure 3-9 on page 15

VDD

TIME

VSS

OUT 1

10k

+5V

SNSK

SNS

SENSE

ELECTRODE

100nF

47nF

100k

Rop

Auto-off time obtained from 5 V chart in Figure 3-9

AT42QT1012

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 Microchip 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 kΩ to 33 kΩ.

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 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) 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

AT42QT1012

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.

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

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

Table 5-1. 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

AT42QT1012

Parameter Description Min Typ Max Units Notes

Tbl Burst length – 1.86 – ms Vdd, Cs and Cx dependent.

See Section 4.2 for capacitor

selection.

Tr Response time – – 100 ms

5.4 Signal Processing

Table 5-2. Vdd = 3.0V, Cs = 10 nF, Cx = 5 pF, Ta = recommended range, unless otherwise noted

Description Min Typ Max Units Notes

Threshold differential 10 counts

Hysteresis 2 counts

Consensus filter length 4 samples

5.5 DC Specifications

Table 5-3. Vdd = 3.0V, Cs = 4.7 nF, Cx = 5 pF, short charge pulse, Ta = recommended range, unless

otherwise noted

Parameter Description Min Typ Max Units Notes

Vdd Supply voltage 1.8 5.5 V

Idd Supply current – 32

124

– μA 1.8 V

2.0 V

3.0 V

4.0 V

5.0 V

Vdds Supply turn-on slope 100 – – V/s Required for proper start-up

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

5.6 Mechanical Dimensions

5.6.1 6-pin SOT23-6

DRAWING NO. REV. TITLE GPC

6ST1 B

1/25/13

TAQ

Package Drawing Contact:

packagedrawings@atmel.com

Notes: 1. This package is compliant with JEDEC specification

MO-178 Variation AB.

2. Dimension D does not include mold Flash, protrusions or

gate burrs. Mold Flash, protrustion or gate burrs shall not

exceed 0.25 mm per end.

3. Dimension b does not include dambar protrusion.

Allowable dambar protrusion shall not cause the lead width

to exceed the maximum b dimension by more than 0.08 mm

4. Die is facing down after trim/form.

MAX NOTE

SYMBOL MIN NOM

COMMON DIMENSIONS

(Unit of Measure = mm)

A – – 1.45

A1 0 – 0.15

A2 0.90 – 1.30

D 2.80 2.90 3.00 2

E 2.60 2.80 3.00

E1 1.50 1.60 1.75

L 0.30 0.45 0.55

e 0.95 BSC

b 0.30 – 0.50 3

c 0.09 – 0.20

q 0° – 8°

Side View

E E1

A2 A

A1 C

0.10

0.25

A2 A

A1 C

0.10

SEE VIEW B

SEATING PLANE

Pin #1 ID

Top View

View B

View A-A

6ST1, 6-lead, 2.90 x 1.60 mm Plastic Small Outline

Package (SOT23)

Note: For the most current package drawings, please see the Microchip Packaging Specification located

at http://www.microchip.com/packaging

AT42QT1012

5.6.2 8-pin UDFN/USON

DRAWING NO. REV. TITLE GPC

8MA4 B

YAG

Package Drawing Contact:

packagedrawings@atmel.com

01/25/13

8MA4, 8-pad, 2.0x2.0x0.6 mm Body, 0.5 mm pitch,

0.9x1.5 mm Exposed ePad, Ultra-Thin Dual Flat

No Lead Package (UDFN/USON)

COMMON DIMENSIONS

(Unit of Measure = mm)

SYMBOL MIN NOM MAX NOTE

A - - 0.60

A10.00 - 0.05

b 0.20 - 0.30

D 1.95 2.00 2.05

D2 1.40 1.50 1.60

E 1.95 2.00 2.05

E2 0.80 0.90 1.00

e 0.50 BSC

L 0.20 0.30 0.40

k 0.20 - -

1. All dimensions are in mm. Angles in degrees.

2. Coplanarity applies to the exposed pad as well as the terminals.

Coplanarity shall not exceed 0.05 mm.

3. Warpage shall not exceed 0.05 mm.

4. Refer to JEDEC MO-236/MO-252.

NOTES:

C0.2

PIN 1 ID

0.05

2 3

678

Top view Bottom view

Side view

Note: For the most current package drawings, please see the Microchip Packaging Specification located

at http://www.microchip.com/packaging

AT42QT1012

5.7 Part Marking

5.7.1 AT42QT1012– 6-pin SOT23-6

Pin 1 ID

Abbreviated

Part Number:

AT42QT

Note: Samples of the AT42QT1012 may also be marked T10E.

5.7.2 AT42QT1012 – 8-pin UDFN/USON

Pin 1 ID

Pin 1

Class code

(H = Industrial,

green NiPdAu)

Die Revision

(Example: “E” shown)

Assembly Location

Code

(Example: “C” shown)

Lot Number Trace

code (Variable text)

Last Digit of Year

(Variable text)

Abbreviated

Part Number:

AT42QT1012

Note: Samples of the AT42QT1012 may also be marked T10

5.8 Part Number

Part Number Description

AT42QT1012(1) 6-pin SOT23 RoHS compliant IC

AT42QT1012-TSHR 6-pin SOT23 RoHS compliant IC

AT42QT1012-MAH 8-pin UDFN/USON RoHS compliant IC

Notes: 1. Marking details:

Top mark 1st line: ddddTY

Top mark 2nd line: wwxxx

dddd= device, special code

T= Type

Y= Year last digit

ww= calendar workweek

xxx = trace code

AT42QT1012

5.9 Moisture Sensitivity Level (MSL)

MSL Rating Peak Body Temperature Specifications

MSL1 260oC IPC/JEDEC J-STD-020

AT42QT1012

6. Associated Documents

For additional information, refer to the following document (downloadable from the Touch Technology

area of the Microchip website, www.microchip.com):

• Touch Sensors Design Guide

• QTAN0002 – Secrets of a Successful QTouch® Design

AT42QT1012

7. Revision History

Revision No. History

Revision A – May 2009 Initial release

Revision B – August 2009 Update for chip revision 2.2

Revision C – August 2009 Minor update for clarity

Revision D – January 2010 Power specifications updated for revision 2.4.1

Revision E – January 2010 Part markings updated

Revision F – February 2010 MSL specification revised

Other minor updates

Revision G – March 2010 Update for chip revision 2.6

Revision H – May 2010 UDFN/USON package added

Revision I – May 2013 Applied new template

DS40001948A – August 2017 Part marking clarification added. Replaces Atmel document 9543I.

AT42QT1012

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Note the following details of the code protection feature on Microchip devices:

• Microchip products meet the specification contained in their particular Microchip Data Sheet.

• Microchip believes that its family of products is one of the most secure families of its kind on the

market today, when used in the intended manner and under normal conditions.

• There are dishonest and possibly illegal methods used to breach the code protection feature. All of

these methods, to our knowledge, require using the Microchip products in a manner outside the

operating specifications contained in Microchip’s Data Sheets. Most likely, the person doing so is

engaged in theft of intellectual property.

• Microchip is willing to work with the customer who is concerned about the integrity of their code.

AT42QT1012

• Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their

code. Code protection does not mean that we are guaranteeing the product as “unbreakable.”

Code protection is constantly evolving. We at Microchip are committed to continuously improving the

code protection features of our products. Attempts to break Microchip’s code protection feature may be a

violation of the Digital Millennium Copyright Act. If such acts allow unauthorized access to your software

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All other trademarks mentioned herein are property of their respective companies.

AT42QT1012

ISBN: 978-1-5224-2071-2

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DSCs, KEELOQ® code hopping devices, Serial EEPROMs, microperipherals, nonvolatile memory and

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systems is ISO 9001:2000 certified.

AT42QT1012

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