QT100-ISG - Atmel - Product.Network

This datasheet is applicable to all revision 3 chips

AT A GLANCE

Number of keys: One

Technology: Patented spread-spectrum charge-transfer (direct mode)

Key outline sizes: 6mm x 6mm or larger (panel thickness dependent); widely different sizes and shapes possible

Electrode design: Solid or ring electrode shapes

Layers required: One

Electrode materials: Etched copper, silver, carbon, Indium Tin Oxide (ITO), Orgacon

†

ink

Electrode Substrates: PCB, FPCB, plastic films, glass

Panel materials: Plastic, glass, composites, painted surfaces (low particle density metallic paints possible)

Panel thickness: Up to 50mm glass, 20mm plastic (electrode size dependent)

Key sensitivity: Settable via capacitor

Interface: Digital output, active high

Moisture tolerance: Good

Power: 2V ~ 5V

Package: 6-pin SOT23-6 RoHS compliant

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

Applications: Control panels, consumer appliances, toys, lighting controls, mechanical switch or button

Patents: QTouch™ (patented Charge-transfer method)

HeartBeat™ (monitors health of device)

†

Orgacon is a registered trademark of Agfa-Gevaert N.V

LQC

QT100_3R0.09_0707

QT100

HARGE

-T

RANSFER

OUCH

™

SNSK

VSS

OUT

VDD

SNS

SYNC/MODE

The QT100 charge-transfer (‘QT’) touch sensor is a self-contained digital IC capable

of detecting near-proximity or touch. It will project a touch or proximity field through

any dielectric like glass, plastic, stone, ceramic, and even most kinds of wood. It can

also turn small metal-bearing objects into intrinsic sensors, making them responsive

to proximity or touch. This capability, coupled with its ability to self-calibrate, can lead

to entirely new product concepts.

It is designed specifically for human interfaces, like control panels, appliances, toys,

lighting controls, or anywhere a mechanical switch or button may be found.

QT100-ISG-40ºC to +85ºC

SOT23-6T

AVAILABLE OPTIONS

2.8 Spread Spectrum

................................... 5

2.7 Response Time

.................................... 5

2.6 Drift Compensation

.................................. 5

2.5 Forced Sensor Recalibration

........................... 4

2.4 Detect Integrator

.................................... 4

2.3 Max On-duration

.................................... 4

2.2 Threshold

........................................ 4

2.1.4 SYNC Mode

..................................... 3

2.1.3 Low Power Mode

.................................. 3

2.1.2 Fast Mode

...................................... 3

2.1.1 Introduction

..................................... 3

2.1 Run Modes

....................................... 3

2 Operation Specifics .................................. 3

1.4.3 Decreasing Sensitivity

............................... 3

1.4.2 Increasing Sensitivity

................................ 3

1.4.1 Introduction

..................................... 3

1.4 Sensitivity

........................................ 3

1.3 Electrode Drive

..................................... 3

1.2 Basic Operation

.................................... 3

1.1 Introduction

....................................... 3

1 Overview ...........................................

5.2 Numbering Convention

.............................. 10

5.1 Changes

........................................ 10

5 Datasheet Control ................................... 9

4.8 Moisture Sensitivity Level (MSL)

......................... 9

4.7 Marking

.......................................... 8

4.6 Mechanical Dimensions

............................... 8

4.5 DC Specifications

................................... 7

4.4 Signal Processing

................................... 7

4.3 AC Specifications

................................... 7

4.2 Recommended Operating Conditions

..................... 7

4.1 Absolute Maximum Specifications

........................ 7

4 Specifications ....................................... 6

3.3 Power Supply, PCB Layout

............................ 6

3.2 Sample Capacitor

................................... 6

3.1 Application Note

.................................... 6

3 Circuit Guidelines .................................... 6

2.9.3 Output Drive

..................................... 5

2.9.2 HeartBeat™ Output

................................ 5

2.9.1 Output

........................................ 5

2.9 Output Features

....................................

lQ2 QT100_3R0.09_0707

Contents

1 Overvie

1.1 Introduction

The QT100 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 a single low cost, noncritical capacitor is

required for operation.

Figure 1.1 shows a basic circuit using the device.

1.2 Basic Operation

The QT100 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 QT100.

1.3 Electrode Drive

For optimum noise immunity, the electrode should only be

connected to SNSK.

In all cases the rule Cs >> Cx must be observed for proper

operation; a typical load capacitance (Cx) ranges from 5-20pF

while Cs is usually about 2-50nF.

Increasing amounts of Cx destroy gain, therefore it is

important to limit the amount of stray 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.

A series resistor, Rs, should be placed in line with SNSK to

the electrode to suppress ESD and EMC effects.

1.4 Sensitivity

1.4.1 Introduction

The sensitivity on the QT100 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.

1.4.2 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. 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 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 destroy 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.

1.4.3 Decreasing Sensitivity

In some cases the QT100 may be too sensitive. In this case

gain can be easily lowered further by decreasing Cs.

2 Operation Specifics

2.1 Run Modes

2.1.1 Introduction

The QT100 has three running modes which depend on the

state of SYNC, pin 6 (high or low).

2.1.2 Fast Mode

The QT100 runs in Fast mode if the SYNC pin is permanently

high. In this mode the QT100 runs at maximum speed at the

expense of increased current consumption. Fast mode is

useful when speed of response is the prime design

requirement. The delay between bursts in Fast mode is

approximately 1ms, as shown in Figure 2.2.

2.1.3 Low Power Mode

The QT100 runs in Low Power (LP) mode if the SYNC line is

held low. In this mode it sleeps for approximately 85ms 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). It then returns to

LP mode after the key touch is resolved as shown in

Figure 2.1.

lQ3 QT100_3R0.09_0707

Figure 1.1 Basic Circuit Configuration

OUT

VDD

SNSK

SNS

SYNC/MODE

VSS

3 1

VDD

SENSE

ELECTRODE

Note: A bypass capacitor should be tightly wired

between Vdd and Vss and kept close to QT100 pin 5.

Figure 2.4 SYNC Mode (Short Pulses)

SNSK

QT100

SYNC

>10us >10us >10us

2.1.4 SYNC Mode

It is possible to synchronize the device to an external clock

source by placing an appropriate waveform on the SYNC pin.

SYNC mode can synchronize multiple QT100 devices to each

other to prevent cross-interference, or it can be used to

enhance noise immunity from low frequency sources such as

50Hz or 60Hz mains signals.

The SYNC pin is sampled at the end of each burst. If the

device is in Fast mode and the SYNC pin is sampled high,

then the device continues to operate in Fast mode

(Figure 2.2). 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 period of the SYNC signal should be longer

than the burst length (Figure 2.3).

However, once SYNC mode has been entered, if the

SYNC signal consists of a series of short pulses (>10µs)

then a burst will only occur on the leading edge of each

pulse (Figure 2.4) instead of on each change of SYNC

signal, as normal (Figure 2.3).

In SYNC mode, the device will sleep after each

measurement burst (just as in LP mode) but will be

awakened by a change in the SYNC signal in either

direction, resulting in a new measurement burst. If SYNC

remains unchanged for a period longer than the LP mode

sleep period (about 85ms), the device will resume

operation in either Fast or LP mode depending on the

level of the SYNC pin (Figure 2.3).

There is no DI in SYNC mode (each touch is a detection)

but the Max On-duration will depend on the time between

SYNC pulses; see Sections 2.3 and 2.4. Recalibration

timeout is a fixed number of measurements so will vary

with the SYNC period.

2.2 Threshold

The internal signal threshold level is fixed at 10 counts of

change with respect to the internal reference level, which

in turn adjusts itself slowly in accordance with the drift

compensation mechanism.

The QT100 employs a hysteresis dropout of two counts

of the delta between the reference and threshold levels.

2.3 Max On-duration

If an object or material obstructs the sense pad the signal

may rise enough to create a detection, preventing further

operation. To prevent this, the sensor includes a timer

which monitors detections. If a detection exceeds the

timer setting the sensor performs a full recalibration. This is

known as the Max On-duration feature and is set to ~80s (at

3V). This will vary slightly with Cs and if SYNC mode is used.

As the internal timebase for Max On-duration is determined by

the burst rate, the use of SYNC can cause dramatic changes

in this parameter depending on the SYNC pulse spacing.

2.4 Detect Integrator

It is desirable to suppress detections generated by electrical

noise or from quick brushes with an object. To accomplish

this, the QT100 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 QT100, the required count is four. In LP mode the

device will switch to Fast mode temporarily in order to resolve

the detection more quickly; after a touch is either confirmed or

denied the device will revert back to normal LP mode

operation automatically.

The DI can also be viewed as a 'consensus' filter, that

requires four successive detections to create an output.

lQ4 QT100_3R0.09_0707

Figure 2.1 Low Power Mode (SYNC held low)

SYNC

SNSK

QT100 sleepsleep sleep

fast detect

integrator

OUT

Key

touch

~85ms

Figure 2.2 Fast Mode Bursts (SYNC held high)

SNSK

QT100

SYNC

~1ms

Figure 2.3 SYNC Mode (triggered by SYNC edges)

SYNC

SNSK

QT100

SNSK

QT100

slow m ode sl eep per iod

sleep

sleepsleep

R evert to Fast M ode

Revert to Slow M ode

slow m ode sl eep per iod

2.5 Forced Sensor Recalibration

The QT100 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 QT100's V

DD pin directly from another

logic gate or a microcontroller port will serve as

both power and 'forced recal'. The source

resistance of most CMOS gates and

microcontrollers are low enough to provide direct

power without problem.

2.6 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 2.5). 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 QT100 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.

The QT100's 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, usually in

only a few seconds.

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.

2.7 Response Time

The QT100's response time is highly dependent on 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. The response time will

also be a lot slower in LP or SYNC mode due to a longer time

between burst measurements.

2.8 Spread Spectrum

The QT100 modulates its internal oscillator by ±7.5 percent

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.

2.9 Output Features

2.9.1 Output

The output of the QT100 is active-high upon detection. The

output will remain active-high for the duration of the detection,

or until the Max On-duration expires, whichever occurs first. If

a Max On-duration timeout occurs first, the sensor performs a

full recalibration and the output becomes inactive (low) until

the next detection.

lQ5 QT100_3R0.09_0707

Figure 2.5 Drift Compensation

Threshold

Signal Hysteresis

Reference

Output

Figure 2.7

Using a micro to obtain HeartBeat pulses in either output state

Figure 2.6

Getting HeartBeat pulses with a pull-up resistor

VDD

OUT

SNS

SYNC/MODE

SNSK

VSS

VDD

HeartBeat™ Pulses

Microcontroller

PORT_M.x

PORT_M.y

OUT

SNS

SYNC/MODE

SNSK

2.9.2 HeartBeat™ Output

The QT100 output has a HeartBeat™ ‘health’ indicator

superimposed on it in both LP and SYNC modes. This

operates by taking the output pin into a three-state mode for

15µs once before every QT burst. This output state can be

used to determine that the sensor is operating properly, or it

can be ignored, using one of several simple methods.

The HeartBeat indicator can be sampled by using a pull-up

resistor on the OUT pin, and feeding the resulting

positive-going pulse into a counter, flip flop, one-shot, or other

circuit. The pulses will only be visible when the chip is not

detecting a touch.

If the sensor is wired to a microcontroller as shown in

Figure 2.7, the microcontroller can reconfigure the load

resistor to either VSS or VDD depending on the output state of

the QT100, so that the pulses are evident in either state.

Electromechanical devices like relays will usually ignore the

short Heartbeat pulse. The pulse also has too low a duty cycle

to visibly affect LEDs. It can be filtered completely if desired,

by adding an RC filter to the output, or if interfacing directly

and only to a high-impedance CMOS input, by doing nothing

or at most adding a small noncritical capacitor from OUT to

VSS.

2.9.3 Output Drive

The OUT pin is active high and can sink or source up to 2mA.

When a large value of Cs (>20nF) is used the OUT current

should be limited to <1mA 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 Circuit Guidelines

3.1 Application Note

Refer to Application Note AN-KD02, downloadable from the

Quantum website for more information on construction and

design methods. Go to http://www.qprox.com, click the

Support tab and then Application Notes.

3.2 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 2nF to 50nF 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 percent tolerance capacitors are recommended. X7R

ceramic types can be obtained in 5 percent tolerance at little

or no extra cost. In applications where high sensitivity (long

burst length) is required the use of PPS capacitors is

recommended.

3.3 Power Supply, PCB Layout

The power supply can range between 2.0V and 5.5V. At 3V

current drain averages less than 500µA in Fast mode.

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

QT100. The QT100 will track slow changes in V

DD, but it can

be badly affected by rapid voltage fluctuations. It is highly

recommended that a separate voltage regulator be used just

for the QT100 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

AN-KD02 (see Section 3.1) 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 discretes, 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.

Important Note: for proper operation a 100nF (0.1µF)

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

device’s power pins.

lQ6 QT100_3R0.09_0707

4 Specifications

4.1 Absolute Maximum Specifications

Operating temp.......................................................................................-40ºC to +85ºC

Storage temp.......................................................................................-55

C to +125

VDD..................................................................................................... 0 to +6.5V

Max continuous pin current, any control or drive pin..............................................................±20mA

Short circuit duration to VSS, any pin............................................................................ infinite

Short circuit duration to VDD, any pin............................................................................infinite

Voltage forced onto any pin...................................................................-0.6V to (VDD + 0.6) Volts

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 s

ecification conditions for extended

eriods ma

affect device reliabilit

4.2 Recommended Operating Conditions

VDD....................................................................................................+2.0 to 5.5V

Short-term supply ripple+noise................................................................................. ±5mV

Long-term supply stability....................................................................................±100mV

Cs value............................................................................................... 2nF to 50nF

Cx value..................................................................................................5 to 20pF

4.3 AC Specifications

VDD = 3.0V, Cs = 10nF, Cx = 5pF, Ta = recommended range, unless otherwise noted

µs15Heartbeat pulse widthTHB

ms100Response timeTR

Vdd, Cs and Cx dependent. See

Section 3.2 for capacitor selection.

ms20Burst lengthTBL

Increases with reducing VDDms85

Time between end of burst and

start of the next (LP mode)

ms1

Time between end of burst and

start of the next (Fast mode)

±7.5% spread spectrum variationµs2Transfer durationTPT

±7.5% spread spectrum variationµs2Charge durationTPC

Cs, Cx dependentms250Recalibration timeTRC

NotesUnitsMaxTypMinDescriptionParameter

4.4 Signal Processing

(At 3V) Will vary in SYNC mode and with

VDD

secs80Max on-duration

samples4Consensus filter length

counts2Hysteresis

counts10Threshold differential

NotesUnitsMaxTypMinDescription

lQ7 QT100_3R0.09_0707

4.5 DC Specifications

VDD = 3.0V, Cs = 10nF, Cx = 5pF, Ta = recommended range, unless otherwise noted

bits149Acquisition resolutionAR

pF1000Load capacitance rangeCX

µA±1Input leakage currentIIL

OUT, 1mA sourceVVDD-0.7High output voltageVOH

OUT, 4mA sinkV0.6Low output voltageVOL

V2.2High input logic levelVHL

V0.8Low input logic levelVIL

Required for proper start-upV/s100Supply turn-on slopeVDDS

µA

Supply current, LP ModeIddl Depending on supply and run modeµA6005Supply currentIDD

V5.252Supply voltageVDD

Notes

UnitsMaxTypMinDescription

Parameter

4.6 Mechanical Dimensions

Aa W

02NN

Pin 1

10º0º10º0ºØ

0.0080.0040.20.09e 0.0220.0140.550.35E 0.020.0140.50.35L 0.038 BSC--0.95 BSC--D 0.00600.150.0h 0.0510.0351.30.9H 0.0690.0591.751.5Aa 0.1180.1023.02.6W 0.1220.1103.102.8M NotesMaxMinNotesMaxMin InchesMillimeters

Symbol

Package type: SOT23-6

lQ8 QT100_3R0.09_0707

4.7 Marking

02NN (where NN is variable)QT100-ISG MarkingSOT23-6 Part Number

4.8 Moisture Sensitivity Level (MSL)

IPC/JEDEC J-STD-020C260

CMSL1 SpecificationsPeak Body TemperatureMSL Rating

lQ9 QT100_3R0.09_0707

5 Datasheet Control

5.1 Changes

Changes this datasheet issue (09)

Front page

Section 3.2

Section 4.1, 4.2, 4.3, 4.4

Section 5.1

5.2 Numbering Convention

Part Number

QT100_MXN.nn_mmyy

Chip Revision

(Where M= Major chip rev ision,

N = minor chip revision,

X = Prereleased Product

[or R = Released Product])

Datasheet Issue Number

Datasheet Release Date;

(Where mm = Month, yy = Year)

A minor chip revision (N) is defined as a revision change which does not affect product functionality or datasheet.

The value of N is only stated for released parts (R).

lQ10 QT100_3R0.09_0707

NOTES:

lQ11 QT100_3R0.09_0707

Patented and patents pending

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The specifications set out in this document are subject to change without notice. All products sold and services supplied by QRG are subject

to QRG’s Terms and Conditions of sale and services. QRG patents, trademarks and Terms and Conditions can be found online at

http://www.qprox.com/about/legal.php. Numerous further patents are pending, one or m ore which may apply to this device or the applications

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Developer: Martin Simmons