QT100A

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AT A GLANCE

Number of keys: One

Technology: Patented spread-spectrum charge-transfer.

Key outline sizes: 6mm x 6mm 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 m aterials: Plastic, glass, composites, painted surfaces (low particle density metallic paints possible)

Panel th ickness: Up to 50mm glass, 20mm plastic (electrode size and Cs dependent)

Key sensitivity: Settable via capacitor (Cs)

Interface: Digital output, active high

Moisture tolerance: Good

Power: 2V ~ 5.5V; 6.5uA @ 2.0V typical

Package: 10 pin MSOP and 6 pin WSON; both are RoHS compliant

Signal processing: Self-calibration, auto drift compensation, noise filtering

Appl icati ons: Control panels, consumer appliances, toys, lighting controls, mechanical switch or button

Patents: QTouch(patented Charge-transfer method)

Copyright 2008 QRG Ltd.QT100A_1R7.01_0308

QT100ACHARGE-TRANSFERQTOUCHIC

The QT100A charge-transfer (QT) touch sensor is a self-contained digital ICcapable of detecting near-proximity or touch. It will project a touch or proximityfield through any dielectric like glass, plastic, stone, ceramic, and even mostkinds of wood. It can also turn small metal-bearing objects into intrinsicsensors, making them responsive to proximity or touch. This capability,coupled with its ability to self-calibrate, can lead to entirely new productconcepts.

It is designed specifically for human interfaces, like control panels, appliances,toys, lighting controls, or anywhere a mechanical switch or button may befound.

This device can also project a proximity field to severa centimeters with theproper electrode and circuit design.

These devices are intended to replace the QT100. Two package types areoffered, one of which can directly replace the QT100s SOT-23-6 package butwith a reduced thickness.

6-WSON Package

10-MSOP Package

VSS

SNSSNSK

VDD

61

2

3 4

5

SYNCOUT

QT100A

VSS

N/C

SNS

SNSK

N/C

N/C

VDD

10

9

8

7

6

1

2

3

4

5

SYNC

N/C

OUT

QT100A

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Table 1.1 Pinlist

-Output stateO110OUT

Leave open - do not connectUnusedO-9N/C

-Sync & Mode InputI6 8SYNC

Always connect to SyncUnusedI- 7N/C-+2.0 ~ +5.5VPowerPwr56VDD

-GroundGroundPwr25VSS



-To CsSense pinI/O42SNS

-To Cs + KeySense pinI/O31SNSK

If UnusedNotesFunctionTypePin

6WSON

Pin

10MSOPName

Pin TypeI CMOS input onlyI/O CMOS I/OO CMOS push-pull outputPwr Power / ground

NotesIn 6-WSON package this pin is internally connected to SYNC pinPin is either Sync or Slow/Fast Mode depending on how strapped; see Section 2.1.

2 Copyright 2008 QRG Ltd.QT100A_1R7.01_0308

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1 Overview

1.1 IntroductionThe QT100A is a digital burst mode charge-transfer (QT)sensor designed specifically for touch controls; it includes allhardware and signal processing functions necessary toprovide stable sensing under a wide variety of changingconditions. Only a single low cost, noncritical capacitor is

required for operation.This device is designed to replace the QT100.

1.1.1 WSON package dif ferences wi th QT100A 6-pin WSON package version is available which uses thesame basic PCB footprint as the QT100s SOT-23-6package. The 6-WSON package has a reduced packagethickness.

In converting an existing design from the QT100 to theQT100A, it should be noted that the 6-WSON package has abottom center pad which must be either grounded(connected to Vss) or isolated. This center pad is wideenough that it can possibly touch the copper pads of the

QT100s SOT-23-6 footprint, potentially creating a shortcircuit between two or more pads. In order to prevent this thesolder mask layer of the PCB under the device should bewidened slightly, or, the copper PCB pads narrowed slightlyto avoid contact with the center pad. The pinout and padplacement however are the same as for the QT100.

An application note is available to assist in this conversionprocess.

A 10-pin MSOP package version is also available.

1.1.2 Electrical differences with QT100The QT100A is behaviorally identical to the QT100, and nochange in the value of Cs is required to achieve the same

sensitivity as the QT100.

1.2 Basic OperationFigure 1.1 shows a basic circuit using the device.

The QT100A employs bursts of charge-transfer cycles toacquire its signal. Burst mode permits power consumption inthe microamp range, dramatically reduces RF emissions,lowers susceptibility to EMI, and yet permits excellentresponse time. Internally the signals are digitally processedto reject impulse noise, using a 'consensus' filter whichrequires four consecutive confirmations of a detection beforethe output is activated.

The QT switches and charge measurement hardware

functions are all internal to the QT100A.

1.3 Electrode DriveFor optimum noise immunity, the electrode should only beconnected to SNSK.

In all cases the rule Cs>>Cx must be observed for properoperation; a typical load capacitance (Cx) ranges from2-20pF while Cs is usually from 2-50nF.

Increasing amounts of Cx destroy gain, therefore it isimportant to limit the amount of stray capacitance on bothSNS terminals. This can be done, for example, by minimizingtrace lengths and widths and keeping these traces away from

power or ground traces or copper pours.

The traces and any components associated with SNS andSNSK will become touch sensitive and should be treated withcaution to limit the touch area to the desired location.

A series resistor, Rs, should be placed in line with SNSK tothe electrode to suppress ESD and EMC effects.

1.4 Sensiti vity

1.4.1 IntroductionThe sensitivity on the QT100A is a function of things like thevalue of Cs, electrode size and capacitance, electrode shapeand orientation, the composition and aspect of the object tobe sensed, the thickness and composition of any overlayingpanel material, and the degree of ground coupling of bothsensor and object.

1.4.2 Increasing SensitivityIn some cases it may be desirable to increase sensitivity; forexample, when using the sensor with very thick panelshaving a low dielectric constant. Sensitivity can often be

increased by using a larger electrode or reducing panelthickness. Increasing electrode size can have diminishingreturns, as high values of Cx will reduce sensor gain.

The value of Cs also has a dramatic effect on sensitivity, andthis can be increased in value with the trade-off of slowerresponse time and more power. Increasing the electrode'ssurface area will not substantially increase touch sensitivity ifits diameter is already much larger in surface area than theobject being detected. Panel material can also be changed toone having a higher dielectric constant, which will better helpto propagate the field.

Ground planes around and under the electrode and its SNSKtrace will cause high Cx loading and destroy gain. The

possible signal-to-noise ratio benefits of ground area aremore 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 strengthand increase Cx loading and should be avoided, if possible.Keep ground away from the electrodes and traces.

1.4.3 Decreasing SensitivityIn some cases the QT100A may be too sensitive. In this casegain can be easily lowered by decreasing Cs.

3 Copyright 2008 QRG Ltd.

QT100A_1R7.01_0308

Figure 1.1 Basic Circui t Configuration

OUT CsSNS

Rs

Cx

SENSEELECTRODE

2 ~ 5V

VDD

SYNC

3

4

*Note: Bypass capacitor Cb should be tightly wiredbetween Vdd and Vss

SNSK

VSS

*Cb QT100A, 6-WSON Pkg.

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2 Operation Specifics

2.1 Run Modes

2.1.1 IntroductionThe QT100A has three running modes which depend on thelogic level applied to the SYNC pin.

2.1.2 Fast Mode (SYNC = 1)The QT100A runs in Fast mode if the SYNC pin ispermanentlyhigh. In this mode the QT100A runs atmaximum speed at the expense of increased currentconsumption. Fast mode is useful when speed of response isthe prime design requirement. The delay between bursts inFast mode is approximately 1ms, as shown in Figure 2.2.

2.1.3 Low Power Mode (SYNC = 0)The QT100A runs in Low Power (LP) mode if the SYNC pinis held low. In this mode it sleeps forapproximately 85ms atthe end of each burst, saving power but slowing response.On detecting a possible key touch, it temporarily switches toFast mode until either the key touch is confirmed or found tobe spurious (via the detect integration process). It thenreturns to LP mode after the key touch is resolved as shownin Figure 2.1.

2.1.4 Sync ModeIt is possible to synchronize the device to an external clocksource by placing an appropriate waveform on the SYNC pin.Sync mode can synchronize multiple QT100A devices toeach other to prevent cross-interference, or it can be used toenhance noise immunity from low frequency sources such as50Hz or 60Hz mains signals.

The Sync pin is sampled at the end of each burst. If thedevice is in Fast mode and the Sync pin is sampled high,then the device continues to operate in Fast mode (Figure2.2). If SYNC is sampled low, then the device goes to sleep.From then on, it will operate in Sync mode (Figure 2.1).Therefore, to guarantee entry into Sync mode the low periodof the Sync signal should be longer than the burst length(Figure 2.3).

However, once Sync mode has been entered, if the Syncsignal consists of a series of short pulses (>10s) then aburst will only occur on the falling edge of each pulse

(Figure2.4).

In Sync mode, the device will sleep after each measurementburst (just as in LP mode) but will be awakened by the fallingedge of the Sync signal, resulting in a new measurementburst. If Sync remains unchanged for a period longer thanthe LP mode sleep period (about 85ms), the device willresume operation in either Fast or LP mode depending onthe level of the Sync pin (Figure 2.3).

There is no DI in Sync mode (each touch is a detection) butthe Max On-duration will depend on the time between Syncpulses; see Sections 2.3 and 2.4. Recalibration timeout is afixed number of measurements so will vary with the Syncperiod.

2.2 ThresholdThe internal signal threshold level is fixed at 13 counts ofchange with respect to the internal reference level, which inturn adjusts itself slowly in accordance with the driftcompensation mechanism.

The QT100A employs a hysteresis dropout of 3 counts of thedelta between the reference and threshold levels.

2.3 Max On-durationIf an object or material obstructs the sense pad the signalmay rise enough to create a detection, preventing furtheroperation. To prevent this, the sensor includes a timer which

monitors detections. If a detection exceeds the timer settingthe sensor performs a full recalibration. This is known as the


QT100A_1R7.01_0308

Figure 2.2 Fast Mode Burs ts

(SYNC held high)

SNSK

QT100A

SYNC

~1ms

Figure 2.1 Low Power Mode

SYNC

SNSK

QT100A

sleepsleep sleep

fast detectintegrator

OUT

Key

touch

~85ms

Figure 2.3 Sync Mode (triggered by negative edges on SYNC)

SYNC

SYNC

SNSKQT100A

slow mode sleep period

sleep

sleep

sleepsleep

sleepsleep

Revert to

Fast Mode

Revert toSlow Mode

slow mode sleep period

SNSK

QT100A

Figure 2.4 Sy nc Mode (Short Pulses)

SNSKQT100A

SYNC

>10us >10us >10us

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Max On-duration feature and is set to ~80s (at 3V). This willvary slightly with Cs and if Sync mode is used. As theinternal timebase for Max On-duration is determined by theburst rate, the use of Sync can cause dramatic changes inthis parameter depending on the Sync pulse spacing.

2.4 Detect IntegratorIt is desirable to suppress detections generated by electricalnoise or from quick brushes with an object. To accomplishthis, the QT100A incorporates a detect integration (DI)counter that increments with each detection until a limit isreached, after which the output is activated. If no detection issensed prior to the final count, the counter is resetimmediately to zero. In the QT100A, the required count isfour. In LP mode the device will switch to Fast modetemporarily in order to resolve the detection more quickly;after a touch is either confirmed or denied the device willrevert back to normal LP mode operation automatically.

The DI can also be viewed as a 'consensus' filter, thatrequires four successive detections to create an output.

2.5 Forced Sensor RecalibrationThe QT100A has no recalibration pin; a forced recalibrationis accomplished when the device is powered up or after therecalibration timeout. However, supply drain is low so it is asimple matter to treat the entire IC as a controllable load;driving the QT100A's Vdd pin directly from another logic gateor a microcontroller port will serve as both power and 'forcedrecal'. The source resistance of most CMOS gates andmicrocontrollers are low enough to provide direct powerwithout problem.

2.6 Drif t CompensationSignal drift can occur because of changes in Cx and Cs overtime. It is crucial that drift be compensated for, otherwise

false detections, nondetections, and sensitivity shifts willfollow.

Drift compensation (Figure 2.5). is performed by making thereference level track the raw signal at a slow rate, but onlywhile there is no detection in effect. The rate of adjustmentmust be performed slowly, otherwise legitimate detectionscould be ignored. The QT100A drift compensates using aslew-rate limited change to the reference level; the thresholdand hysteresis values are slaved to this reference.

Once an object is sensed, the drift compensation mechanismceases since the signal is legitimately high, and thereforeshould not cause the reference level to change.

The QT100A's drift compensation is 'asymmetric'; thereference level drift-compensates in one direction faster than

it does in the other. Specifically, it compensates faster fordecreasing signals than for increasing signals. Increasingsignals should not be compensated for quickly, since anapproaching finger could be compensated for partially orentirely before even approaching the sense electrode.However, an obstruction over the sense pad, for which thesensor has already made full allowance, could suddenly beremoved leaving the sensor with an artificially elevatedreference level and thus become insensitive to touch. In thislatter case, the sensor will compensate for the object'sremoval very quickly, usually in only a few seconds.

With large values of Cs and small values of Cx, driftcompensation will appear to operate more slowly than with

the converse. Note that the positive and negative driftcompensation rates are different.

2.7 Response TimeThe QT100A's response time is highly dependent on runmode and burst length, which in turn is dependent on Cs andCx. With increasing Cs, response time slows, whileincreasing levels of Cx reduce response time. The responsetime will also be a lot slower in LP or Sync mode due to alonger time between burst measurements.


QT100A_1R7.01_0308

Figure 2.6Getting HeartBeat pulses with a pull-up resistor

6

4

VDD

31OUT

SNS

SYNC

SNSK

VSS

VDD

2

Ro

HeartBeat Pulses

5

Figure 2.7Using a micro to obtain HeartBeat pulses in either output state

3

4

SYNC

SNS

6

SNSKOUTR0

Microcontroller

Port_M.x

Port_M.y

1

Figure 2.5 Drif t Compensation

Threshold

SignalHysteresis

Reference

Output

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2.8 Spread SpectrumThe QT100A modulates its internal oscillator by 7.5percentduring the measurement burst. This spreads the generatednoise over a wider band reducing emission levels. This alsoreduces susceptibility since there is no longer a singlefundamental burst frequency.

2.9 Output Features

2.9.1 OutputThe output of the QT100A is active-high upon detection. Theoutput will remain active-high for the duration of thedetection, or until the Max On-duration expires, whicheveroccurs first. If a Max On-duration timeout occurs first, thesensor performs a full recalibration and the output becomesinactive (low) until the next detection.

2.9.2 HeartBeat OutputThe QT100A output has a HeartBeat health indicatorsuperimposed on it in all modes. This operates by taking theoutput pin into a three-state mode for 15s once before everyQT burst. This output state can be used to determine that thesensor is operating properly, or it can be ignored, using oneof several simple methods.

The HeartBeat indicator can be sampled by using a pull-upresistor on the OUT pin, and feeding the resultingpositive-going pulse into a counter, flip flop, one-shot, orother circuit. The pulses will only be visible when the chip isnot detecting a touch.

If the sensor is wired to a microcontroller as shown inFigure2.7, the microcontroller can reconfigure the loadresistor to either Vss or Vdd depending on the output state ofthe QT100A, so that the pulses are evident in either state.

Electromechanical devices like relays will usually ignore theshort Heartbeat pulse. The pulse also has too low a duty

cycle to visibly affect LEDs. It can be fil tered completely ifdesired, by adding an RC filter to the output, or if interfacingdirectly and only to a high-impedance CMOS input, by doingnothing or at most adding a small noncritical capacitor fromOUT to Vss.

2.9.3 Output DriveThe OUT pin is active high and can sink or source up to2mA. When a large value of Cs (>20nF) is used the OUTcurrent should be limited to

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4 Specifications

4.1 Absolute Maximum SpecificationsOperating temp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -40OC to +85OCStorage temp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55OC to +125OCVDD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 to +6.0VMax continuous pin current, any control or drive pin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mAShort circuit duration to VSS, any pin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . infinite

Short circuit duration to VDD, any pin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . infiniteVoltage forced onto any pin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.6V to (VDD+ 0.6) Volts

4.2 Recommended Operating Condit ionsVDD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +2.0 to 5.5VShort-term supply ripple+noise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5mV

L o n g - te rm s u p p l y s ta b i l i t y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 0 mVCs value. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2nF to 50nFCx value. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 to 50pF

4.3 AC Specif icationsVDD= 3.0V, Cs = 10nF, Cx = 5pF, Ta = recommended range, unless otherwise noted

s15Heartbeat pulse widthTHB

ms100Response timeTR

Vdd, Cs and Cx dependentms20Burst lengthTBL

Increases with decreasing VDDms85Time between end of burst andstart of the next (LP mode)

TG2

ms1Time between end of burst and

start of the next (Fast mode)

TG1

7.5% spread spectrum variations2Transfer durationTPT

7.5% spread spectrum variations2Charge durationTPC

Cs, Cx dependentms250Recalibration timeTRC

NotesUnitsMaxTypMinDescriptionParameter

4.4 Signal Processing

Will vary in SYNC mode, and with VDDsecs80Max on-duration

samples4Consensus filter length

See Note 1counts3Hysteresis

See Note 1counts13Threshold differential

NotesUnitsMaxTypMinDescription

Note1: These threshold and hysteresis values exactly match the performance of the QT100..


CAUTION: Stresses beyond those listed under Absolute Maximum Specifications may cause permanentdamage to the device. This is a stress rating only and functional operation of the device at these or otherconditions beyond those indicated in the operational sections of this specification is not implied. Exposure toabsolute maximum s ecification conditions for extended eriods ma affect device reliabilit .

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4.5 DC Specif icationsVDD= 3.0V, Cs = 10nF, Cx = 5pF, Ta = recommended range, unless otherwise noted

bits149Acquisition resolutionAR

pF1000Load capacitance rangeCX

A1Input leakage currentIIL

OUT, 1mA sourceVVDD-0.7High output voltageVOH

OUT, 4mA sinkV0.6Low output voltageVOL

SYNC pinV2.2High input logic levelVHL

SYNC pinV0.8Low input logic levelVILRequired for proper start-upV/s100Supply turn-on slopeVDDS

2V3V5V

A126.5

1745

Supply current, LP ModeIddl

3VA600Supply current, Fast modeIDD

NotesUnitsMaxTypMinDescriptionParameter

4.6 Mechanical Dimensions


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4.7 Part Marking

4.8 Order Codes

4.9 Moisture Sensit ivity Level (MSL)

IPC/JEDEC J-STD-020C260OCMSL3

TBDTBDMSL1

SpecificationsPeak Body TemperatureMSL Rating


6-Pin WSON Package

E

D

yA1

A

C

0.45

R0.2

b

D2

E2

L

e

12

C

(b1)

0.55

(1.55)

(0.525)

0.075-0.00y

0.400.350.30L

-0.95-e

1.451.401.35E2

3.053.002.95E

2.352.302.25D2

3.053.002.95D

-0.20 Ref-c

-0.20-b1

0.500.450.40b0.050.020.00A1

0.800.750.70A

Max.Nom.Min.

Dimensions in mmSymbol

MSL3QT100A-ISG6-WSON Package

MSL1QT100A-ISMG10-MSOP Package

MSL RatingOrder CodeDevice Package

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Copyright 2008 QRG Ltd. All rights reservedPatented

Corporate Headquarters1 Mitchell Point

Ensign Way, Hamble SO31 4RFGreat Britain

Tel: +44 (0)23 8056 5600 Fax: +44 (0)23 8045 3939

www.qprox.com

The specifications set out in this document are subject to change without notice. All products sold and services supplied by QRG are subject toQRGs Terms and Conditions of sale and services. QRG patents, trademarks and Terms and Conditions can be found online athttp://www.qprox.com/about/legal.php. Numerous further patents are pending, one or more which may apply to this device or the applications thereof.

QRG products are not suitable for medical (including lifesaving equipment), safety or mission critical applications or other similar purposes. Except asexpressly set out in QRG's Terms and Conditions, no licenses to patents or other intellectual property of QRG (express or implied) are granted byQRG in connection with the sale of QRG products or provision of services. QRG will not be liable for customer product design and customers areentirely responsible for their products and applications which incorporate QRG's products.

Development Team: Luben Hristov, Keith Br itton, Hal Philipp

QT100A

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