QT161-D - Quantum Research Group

lQQProx™ QT160 / QT161

6 K

HARGE

-T

RANSFER

OUCH

™ S

ENSOR

APPLICATIONS



Instrument panels



Gaming machines



Access systems



Pointing devices



Appliance controls



Security systems



PC Peripherals



Backlighted buttons

QT160 / QT161 charge-transfer (“QT’”) QTouch ICs are self-contained digital controllers capable of detecting near-proximity or

touch from up to 6 electrodes. They allow electrodes to project 6 independent sense fields through any dielectric like glass,

plastic, stone, ceramic, and wood. They can also make metal-bearing objects responsive to proximity or touch by turning them

into intrinsic sensors. These capabilities coupled with continuous self-calibration can lead to entirely new product concepts,

adding high value to product designs.

Each of the 6 channels operate independently of the others, and each can be tuned for a unique sensitivity level by simply

changing its sample capacitor value.

The devices are designed specifically for human interfaces, like control panels, appliances, gaming devices, lighting controls,

or anywhere a mechanical switch or button may be found; they may also be used for some material sensing and control

applications. The option-selectable toggle mode permits on/off touch control, for example for light switch replacement.

The devices require only a common inexpensive capacitor per channel in order to function. The QT160 also offers the unique

adjacent key suppression (AKS™, patent pending) feature which suppresses touch from weaker responding keys and allows

only a dominant key to detect, for example to solve the problem of large fingers on tightly spaced keys.

In most cases the power supply need only be minimally regulated, for example by an inexpensive 3-terminal regulator.

The RISC core of these devices employ signal processing techniques pioneered by Quantum; these are specifically designed

to make the device survive real-world challenges, such as ‘stuck sensor’ conditions and signal drift.

By using the charge transfer principle, these parts deliver a level of performance clearly superior to older technologies yet are

highly cost-effective.

QT160/161 1.06/1102

6 completely independent touch circuits

Individual logic outputs per channel (active high)

Projects prox fields through any dielectric

Only one external capacitor required per channel

Sensitivity easily adjusted on a per-channel basis

100% autocal for life - no adjustments required

3-5.5V, 5mA single supply operation

Toggle mode for on/off control (strap option)

10s, 60s, infinite auto-recal timeout (strap options)

AKS™ Adjacent Key Suppression (QT160)

Less expensive per key than many mechanical switches

Eval board with backlighting - p/n E160

QT161-AS-40

C to +105

QT161-D

C to +70

QT160-AS-40

C to +105

QT160-D

C to +70

DIP-28SSOP-28T

AVAILABLE OPTIONS

NOTE: Pinout

are not the same

1 - OVERVIEW

QT160/161 is a 6-channel burst mode digital charge-transfer

(QT) sensor designed specifically for touch controls; they

include all hardware and signal processing functions

necessary to provide stable sensing under a wide variety of

conditions. Only a single low cost, non-critical capacitor per

channel is required for operation.

Figure 1-1 shows the basic circuit using the device. See

Tables 7-1 and 7-2 (page 11) for pin listings. The DIP and

SOIC pinouts are not the same and serious damage can

occur if a part is mis-wired).

1.1 BASIC OPERATION

The devices employ bursts of charge-transfer cycles to

acquire signals. Burst mode permits low power operation,

dramatically reduces RF emissions, lowers susceptibility to

RF fields, and yet permits excellent speed. Internally, signals

are digitally processed to reject impulse noise using a

'consensus' filter that requires three consecutive

confirmations of detection. Each channel is measured in

sequence starting with channel 1.

The QT switches and charge measurement hardware

functions are all internal to the device (Figure 1-2). A 14-bit

single-slope switched capacitor ADC includes both the

required QT charge and transfer switches in a configuration

that provides direct ADC conversion. The ADC is designed

to dynamically optimize the QT burst length according to the

rate of charge buildup on Cs, which in turn depends on the

values of Cs, Cx, and Vdd. Vdd is used as the charge

reference voltage. Larger values of Cx cause the charge

transferred into Cs to rise more rapidly, reducing available

resolution; as a minimum resolution is required for proper

operation, this can result in dramatically reduced apparent

gain. Conversely, larger values of Cs reduce the rise of

differential voltage across it, increasing available resolution

by permitting longer QT bursts. The value of Cs can thus be

increased to allow larger values of Cx to be tolerated. The IC

is responsive to both Cx and Cs, and changes in Cs can

result in substantial changes in sensor gain.

Option pins allow the selection of several timing features.

1.2 ELECTRODE DRIVE

The devices have 6 independent channels. The internal ADC

treats Cs on each channel as a floating transfer capacitor; as

a direct result, the sense electrode can be connected to

either SNS1A or SN1B with no performance difference. In

both cases the rule Cs >> Cx must be observed for proper

operation. The polarity of the charge buildup across Cs

during a burst is the same in either case.

It is possible to connect separate Cx and Cx’ loads to

SNS1A and SNS1B simultaneously, although the result is no

different than if the loads were connected together at SNS1A

(or SNS1B). It is important to limit the amount of stray

capacitance on both terminals, especially if the load Cx is

already large, for example by minimizing trace lengths and

widths so as not to exceed the Cx load specification and to

allow for a larger sensing electrode size if so desired.

Unused channels: If a channel is not used, a dummy

nominal 1nF sense capacitor of any type must be connected

to the SNS pins ensure correct operation.

The PCB traces, wiring, and any components associated

with or in contact with SNS1A and SNS1B will become touch

sensitive and should be treated with caution to limit the touch

area to the desired location. Multiple touch electrodes can be

used, for example to create a control button on both sides of

an object, however it is impossible for the sensor to

distinguish between the two touch areas.

1.3 KEY DESIGN

1.3.1 K

EOMETRY

AND

IZE

There is no restriction on the shape of the key electrode; in

most cases common sense and a little experimentation can

result in a good electrode design. The devices will operate

equally well with long, thin keys as with round or square

ones; even random shapes are acceptable. The electrode

can also be a 3-dimensional surface or object. Sensitivity is

related to the amount of surface metallization, touch contact

area, overlying panel material and thickness, and ground

coupling quality of the sensor

circuit.

If a relatively large touch area is

desired, and if tests show that

the electrode has more

capacitance than the part can

tolerate, the electrode can be

made into a sparse mesh (Figure

1-3) having lower Cx than a solid

plane.

1.3.2 B

ACKLIGHTING

EYS

Touch pads can be

back-illuminated quite readily

using electrodes with a hole in

the middle (Figure 1-4). The

holes can be as large as 4 cm in

diameter provided that the ring of

metal is at least twice as wide as

the thickness of the overlying

panel, and the panel is greater

than 1/8 as thick as the diameter

of the hole. Thin panels do not

work well with this method they

2 QT160/161 1.06/1102

Figure 1-1 Recommended Basic Circuit (SSOP Package)

do not propagate fields laterally very well, and will have poor

sensitivity in the middle. Experimentation is required.

Since the channels acquire their signals in time-sequence,

any of the 6 electrodes can be placed in direct proximity to

each other if desired without cross-interference.

A good example of backlighting can be found in the E160

eval board for the QT160.

1.3.3 K

IRCHOFF

’

URRENT

Like all capacitance sensors, these parts rely on Kirchoff’s

Current Law (Figure 1-5) to detect the change in capacitance

of the electrode. This law as applied to capacitive sensing

requires that the sensor’s field current must complete a loop,

returning back to its source in order for capacitance to be

sensed. Although most designers relate to Kirchoff’s law with

regard to hardwired circuits, it applies equally to capacitive

field flows. By implication it requires that the signal ground

and the target object must both be coupled together in some

manner for a capacitive sensor to operate properly. Note that

there is no need to provide actual hardwired ground

connections; capacitive coupling to ground (Cx1) is always

sufficient, even if the coupling might seem very tenuous. For

example, powering the sensor via an isolated transformer

will provide ample ground coupling, since there is

capacitance between the windings and/or the transformer

core, and from the power wiring itself directly to 'local earth'.

Even when battery powered, just the physical size of the

PCB and the object into which the electronics is embedded

will generally be enough to couple a few

picofarads back to local earth.

Electrodes connected to the IC

themselves act as coupling plates back

to local ground, since when one

channel is sensing the other channels

are clamped to circuit ground.

1.3.4 V

IRTUAL

APACITIVE

ROUNDS

When detecting human contact (e.g. a

fingertip), grounding of the person is

never required. The human body

naturally has several hundred

picofarads of ‘free space’ capacitance

to the local environment (Cx3 in Figure

1-5), which is more than two orders of

magnitude greater than that required to

create a return path to the IC via earth.

The PCB however can be physically

quite small, so there may be little ‘free

space’ coupling (Cx1 in Figure 1-5)

between it and the environment to

complete the return path. If the circuit ground cannot be

earth grounded by wire, for example via the supply

connections, then a ‘virtual capacitive ground’ may be

required to increase return coupling.

A ‘virtual capacitive ground’ can be created by connecting

the IC's own circuit ground to:

(1) A nearby piece of metal or metallized housing;

(2) A floating conductive ground plane;

(3) A nail driven into a wall;

(4) A larger electronic device (to which its output might be

connected anyway).

Free-floating ground planes such as metal foils should

maximize exposed surface area in a flat plane if possible. A

square of metal foil will have little effect if it is rolled up or

crumpled into a ball. Virtual ground planes are more effective

and can be made smaller if they are physically bonded to

other surfaces, for example a wall or floor.

1.3.5 F

IELD

HAPING

The electrode can be prevented from sensing in undesired

directions with the assistance of metal shielding connected

3 QT160/161 1.06/1102

Figure 1-2 Internal Switching & Timing

SNS2

SNS1

ELECTRODE

Single-Slope 14-bit

Switched Capacitor AD C

Charge

Amp

Burst Controller

Result

Done

Start

Figure 1-3 Mesh Key Geometry

Figure 1-4 Open Electrode for Back-Illumination

to circuit ground (Figure 1-6). For example, on flat surfaces,

the field can spread laterally and create a larger touch area

than desired. To stop field spreading, it is only necessary to

surround the touch electrode on all sides with a ring of metal

connected to circuit ground; the ring can be on the same or

opposite side from the electrode. The ring will kill field

spreading from that point outwards.

If one side of the panel to which the electrode is fixed has

moving traffic near it, these objects can cause inadvertent

detections. This is called ‘walk-by’ and is caused by the fact

that the fields radiate from either surface of the electrode

equally well. Again, shielding in the form of a metal sheet or

foil connected to circuit ground will prevent walk-by; putting a

small air gap between the grounded shield and the electrode

will keep the value of Cx lower and is encouraged. In the

case of the QT160/161, sensitivity can be high enough

(depending on Cx and Cs) that 'walk-by' signals are a

concern; if this is a problem, then some form of rear

shielding may be required.

1.3.6 S

ENSITIVITY

Sensitivity can be altered to suit various applications and

situations on a channel-by-channel basis. The easiest and

most direct way to impact sensitivity is to alter the value of

Cs. More Cs yields higher sensitivity.

1.3.6.1 Alternative Ways to Increase Sensitivity

Sensitivity can also be increased by using bigger electrodes,

reducing panel thickness, or altering panel composition.

Increasing electrode size can have diminishing returns, as

high values of Cx counteract sensor gain. Also, 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. The panel or

other intervening material can be made thinner, but again

there are diminishing rewards for doing so. Panel material

can also be changed to one having a higher dielectric

constant, which will help propagate the field through to the

front. Locally adding some conductive material to the panel

(conductive materials essentially have an infinite dielectric

constant) will also help; for example, adding carbon or metal

fibers to a plastic panel will greatly increase frontal field

strength, even if the fiber density is too low to make the

plastic bulk-conductive.

1.3.6.2 Decreasing Sensitivity

In some cases the QT160 may be too sensitive. In this case

gain can be lowered further by a number of strategies:

a) making the electrode smaller, b) making the electrode into

a sparse mesh using a high space-to-conductor ratio (Figure

1-3), or c) by decreasing the Cs capacitors.

2 - QT160/QT161 SPECIFICS

2.1 SIGNAL PROCESSING

The QT160 processes all signals using 16 bit math, using a

number of algorithms pioneered by Quantum. The algorithms

are specifically designed to provide for high survivability in

the face of adverse environmental changes.

2.1.1 D

RIFT

OMPENSATION

LGORITHM

Signal drift can occur because of changes in Cx, Cs, and

Vdd over time. If a low grade Cs capacitor is chosen, the

signal can drift greatly with temperature. If keys are subject

to extremes of temperature and humidity, the signal can also

shift. It is crucial that drift be compensated, else false

detections, non-detections, and sensitivity shifts will follow.

Drift compensation (Figure 2-1) is a method that makes the

reference level track the raw signal at a slow rate, only while

no detection is in effect. The rate of reference adjustment

must be performed slowly else legitimate detections can also

be ignored. The IC drift compensates each channel

independently 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 signal 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

4 QT160/161 1.06/1102

Figure 1-6 Shielding Against Fringe Fields

Sense

wire

Sense

wire

Figure 1-5 Kirchoff's Current Law

Sense Electrode

Su rro und ing environm ent

SENSOR

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 for, 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.

2.1.2 T

HRESHOLD

ALCULATION

The internal threshold level is fixed at 6 counts for all

channels. These IC's employ a fixed hysteresis of 2 counts

below the threshold (33%).

2.1.3 M

-D

URATION

If an object or material contacts a sense pad the signal may

rise enough to trigger an output, preventing further normal

operation. To prevent this ‘stuck key’ condition, the sensor

includes a timer on each channel to monitors detections. If a

detection exceeds the timer setting, the timer causes the

sensor to perform a full recalibration (when not set to

infinite). This is known as the Max On-Duration feature.

After the Max On-Duration interval, the sensor channel will

once again function normally, even if partially or fully

obstructed, to the best of its ability given electrode

conditions. There are three timeout durations available via

strap option: 10s, 60s, and infinite (disabled) (Table 2-1).

Max On-Duration works independently per channel; a

timeout on one channel has no effect on another channel

except when the AKS feature is impacted on an adjacent

key. Note also that the timings in Table 2-1 are dependent

on the oscillator frequency: Doubling the recommended

frequency will halve the timeouts.

Infinite timeout is useful in applications where a prolonged

detection can occur and where the output must reflect the

detection no matter how long. In infinite timeout mode, the

designer should take care to be sure that drift in Cs, Cx, and

Vdd do not cause the device to ‘stick on’ inadvertently even

when the target object is removed from the sense field.

The delay timings for max on-duration will increase if the

total duration of all bursts is greater than 33ms, i.e. an

average of 5.5ms per channel.

2.1.4 D

ETECTION

NTEGRATOR

It is desirable to suppress detections generated by electrical

noise or from quick brushes with an object. To accomplish

this, the IC's incorporate a detect integration

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

QT160/161, the required count is 3.

The Detection Integrator can also be viewed as a

'consensus' filter, that requires three detections in

three successive bursts to create an output.

2.1.5 F

ORCED

ENSOR

ECALIBRATION

Pin 28 is a Reset pin, active-low, which in cases

where power is clean can be simply tied to Vdd. On

power-up, the device will automatically recalibrate

all 6 channels of sensing.

Pin 28 can also be controlled by logic or a microcontroller to

force the chip to recalibrate, by toggling it low for 5µs then

raising it high again.

The option pins are read by the IC once each acquisition

cycle and can be changed during operation.

2.1.6 R

ESPONSE

IME

Response time is fixed at 99ms at a 10MHz clock. Response

time can be altered by changing the clock frequency.

Doubling the recommended clock frequency to 20MHz will

halve the response time to 49ms.

Response time will become slower if the total duration of all

bursts is greater than 33ms, i.e. an average of 5.5ms per

channel.

2.2 OUTPUT FEATURES

The ICs are designed for maximum flexibility and can

accommodate most popular sensing requirements. These

are selectable using strap options on pins OPT1 and OPT2.

All options are shown in Table 2-1.

2.2.1 DC M

ODE

UTPUT

The outputs of these ICs can respond in a DC mode, where

they are active upon detection. The output will remain active

for the duration of the detection, or until the Max On-Duration

expires (if not infinite), whichever occurs first. If a max

on-duration timeout occurs first, the sensor performs a full

recalibration and the output becomes inactive until the next

detection.

2.2.2 T

OGGLE

ODE

UTPUT

This makes the sensor respond in an on/off mode like a flip

flop. It is most useful for controlling power loads, for example

in kitchen appliances, power tools, light switches, etc.

Max On-Duration in Toggle mode is fixed at 10 seconds.

When a timeout occurs, the sensor recalibrates but leaves

the output state unchanged.

2.2.3 O

UTPUT

RIVE

The outputs are active-high and can source 1mA and sink

5mA of non-inductive current. If inductive loads are used,

such as small relays, the inductances should be diode

clamped to prevent damage. When set to operate in a

proximity mode (at high gain) Out currents should be limited

to 1mA to prevent gain shifting side effects from occurring,

which happens 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 as described below.

5 QT160/161 1.06/1102

Figure 2-1 Drift Compensation

Threshold

Signal Hysteresis

Reference

Output

Care should be taken when the IC and the loads are both

powered from the same supply, and the supply is minimally

regulated. The QT160/161 derives its internal references

from the power supply, and sensitivity shifts can occur with

changes in Vdd, as happens when loads are switched on.

This can induce detection ‘cycling’, whereby an object is

detected, the load is turned on, the supply sags, the

detection is no longer sensed, the load is turned off, the

supply rises and the object is reacquired, ad infinitum. To

prevent this occurrence, the Out pins should only be lightly

loaded if the device is operated from an unregulated supply,

e.g. batteries. Detection ‘stiction’, the opposite effect, can

occur if a load is shed when an Out pin is active.

The outputs of the IC can directly drive LEDs with series

resistors. The LEDs should be connected with anodes to the

outputs and cathodes towards Vss, so that it lights when the

sensor is active.

2.3 AKS™ - Adjacent Key suppression

The QT160 (not QT161) features adjacent key suppression

for use in applications where keys are tightly spaced. If keys

are very close and a large finger touches one key, the keys

on either side might also activate. AKS stops detections on

adjacent keys by comparing relative signal levels among

them and choosing the key with the largest signal strength.

Key number 1 will cause a suppression of keys 6 and 2. Key

number 2 will cause a suppression of keys 1 and 3. Key 3

will cause a suppression of keys 2 and 4 and so on.

When a touch is detected on a key, but just before the

corresponding OUT pin is activated, a check is made for a

detection on the adjacent keys. If OUT is active on one or

both of the adjacent keys, or if a signal of greater strength is

found on them, the key is suppressed. This means that it is

not possible to activate both keys 3 and 4 for example; if 4 is

already on when 3 is touched, key 3 will be suppressed.

Likewise, if keys 3 and 4 are both touched, but 3 has a

weaker signal than 4 at the moment the decision is made,

then only key 4 will detect and 3 will be suppressed. Once

the detected key is released, the other key is free to detect.

Drift compensation also ceases for the key or keys which

have been suppressed, so long the signal on it is greater

than its threshold level.

This feature is also very effective on water films which bridge

over adjacent keys. When touching one key a water film will

‘transport’ the touch to the adjacent keys covered by the

same film. These side keys will receive less signal strength

than the key actually being touched, and so they will be

suppressed even if the signal they are detecting is large

enough to otherwise cause an output.

3 - CIRCUIT GUIDELINES

3.1 SAMPLE CAPACITOR

Charge sampler caps Cs can be virtually any plastic film or

low to medium-K ceramic capacitor. The acceptable Cs

range is from 10nF to 47nF depending on the sensitivity

required; larger values of Cs demand higher stability to

ensure reliable sensing. Acceptable capacitor types include

polyester film, PPS film, or NP0 / C0G ceramic.

3.2 OPTION STRAPPING

The option pins OPT1 and OPT2 should never be left

floating. If they are floated, the device can draw excess

power and the options will not be properly read.

See Table 2-1 for options. Note that the timings shown are

depend inversely on the oscillator frequency: Doubling the

recommended frequency will halve the timeouts.

3.3 POWER SUPPLY, PCB LAYOUT

The power supply can range from 4.5 to 5.5 volts. If this

fluctuates slowly with temperature, the QT160/161 will track

and compensate for these changes automatically with only

minor changes in sensitivity.

If the power supply is shared with another electronic system,

care should be taken to assure that the supply is free of

digital spikes, sags, and surges which can adversely affect

the IC. The QT160/161 will track slow changes in Vdd, but it

can be seriously affected by rapid voltage steps.

The supply is best locally regulated using a conventional

78L05 type regulator, or almost any 3-terminal LDO device

from 3V to 5V.

For proper operation a 0.1µF or greater bypass capacitor

should be used between Vdd and Vss; the bypass cap

should be placed very close to the device’s power pins.

3.4 OSCILLATOR

The oscillator should be a 10MHz resonator with ceramic

capacitors to ground on each side. 3-pin resonators with

built-in capacitors designed for the purpose are inexpensive

and commonly found. Manufacturers include AVX, Murata,

Panasonic, etc.

Alternatively an external clock source can be used in lieu of

a resonator. The OSC_I pin should be connected to the

external clock, and OSC_O should be left unconnected.

These ICs are fully synchronous, clocked devices that

operate all sections from the OSC_I clock. If the frequency of

OSC_I is changed, all timings will also change in direct

proportion, from the charge and transfer times to the

detection response times and the max on-duration timings.

3.5 UNUSED CHANNELS

Unused signal channels should not be left open. They

should have a small value non-critical dummy Cs capacitor

connected to their SNS pins to allow the internal circuit to

continue to function properly. A nominal value of 1nF

(1,000pF) X7R will suffice.

Unused channels should not have sense traces or

electrodes connected to them.

6 QT160/161 1.06/1102

infiniteGndGnd

DC Out

10sVddVdd

Toggle

60sGndVdd

DC Out

10sVddGnd

DC Out

Max On-DurationOPT2OPT1

Table 2-1 Strap Options

3.6 ESD PROTECTION

In cases where the electrode is placed behind a dielectric

panel, the IC will be protected from direct static discharge.

However even with a panel, transients can still flow into the

electrodes via induction, or in extreme cases via dielectric

breakdown. Porous materials may allow a spark to tunnel

right through the material. Testing is required to reveal any

problems. The device does have diode protection on its SNS

pins which absorb and protect the device from most induced

discharges, up to 20mA; the usefulness of the internal

clamping will depending on the dielectric properties, panel

thickness, and rise time of the ESD transients.

In extreme cases ESD dissipation can be aided further with

added series resistors in line with the electrodes as shown in

Figure 1-1. Because the charge time is 1.2 µs, the circuit can

tolerate large values of series-R, up to 20k ohms in cases

where electrode Cx load is below 10pF. Extra diode

protection at the electrodes can also be used, but this often

leads to additional RFI problems as the diodes will rectify RF

signals into DC which will disturb the measurement.

Directly placing semiconductor transient protection devices

or MOV's on the sense leads is not advised; these devices

have extremely large amounts of nonlinear parasitic C which

will swamp the capacitance of the electrode.

Series-R’s should be low enough to permit at least 6 RC

time-constants to occur during the charge and transfer

phases, where R is the added series-R and C is the load Cx.

If the device is connected to an external control circuit via a

cable or long twisted pair, it is possible for ground-bounce to

cause damage to the Out pins and/or interfere with key

sensing. Noise current injection into the power supply is best

dealt with by shunting the noise aside to chassis ground with

capacitors, and limited using resistors or ferrites.

3.7 RFI PROTECTION

PCB layout, grounding, and the structure of the input circuitry

have a great bearing on the success of a design that can

withstand strong RF interference.

The circuit is remarkably immune to RFI provided that certain

design rules be adhered to:

1. Use SMT components to minimize lead lengths.

2. Always use a ground plane under and around the circuit

and along the sense lines, that is as unbroken as

possible except for relief under and beside the sense

lines to reduce total Cx. Relieved rear ground planes

should be ‘mended’ by bridging over them at 1cm

intervals with 0.5mm ‘rungs’ like a ladder.

3. Ground planes should be connected only to a common

point near the Vss pins of the IC.

4. Route sense traces away from other traces or wires that

are connected to other circuits.

5. Sense electrodes should be kept away from other

circuits and grounds which are not directly connected to

the sensor’s own circuit ground; other grounds will

appear to float at high frequencies and couple RF

currents into the sense lines.

6. Keep the 6 Cs sampling capacitors and all series-R

components close to the IC.

7. Use a 0.1µF minimum ceramic bypass cap very close to

the QT160/161 supply pins.

8. Use series-R’s in the sense lines, of as large a value as

the circuit can tolerate.

9. Bypass input power to chassis ground and again at

circuit ground to reduce line-injected noise effects.

Ferrites over the power wiring may be required to

attenuate line injected noise.

Achieving RF immunity mostly requires diligence and a good

working knowledge of grounding, shielding, and layout

techniques.

7 QT160/161 1.06/1102

4.1 ABSOLUTE MAXIMUM SPECIFICATIONS

Operating temp.................................................................. as designated by suffix

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

C to +125

..................................................................................... -0.5 to +7.0V

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

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

Short circuit duration to V

, any pin.............................................................. infinite

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

4.2 RECOMMENDED OPERATING CONDITIONS

......................................................................................+3.0 to 5.5V

Operating temperature range, 4.5V - 5.5V (QT160-AS, QT161-AS)............................... -40 - +105C

Operating temperature range, 3.0V - 4.5V (QT160-AS, QT161-AS)................................ -40 - +85C

Operating temperature range (QT160-D, QT161-D)............................................... 0 - +70C

Operating frequency, 4.5V - 5.5V.............................................................. 4 - 20MHz

Operating frequency, 3.0V - 5.5V.............................................................. 4 - 10MHz

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

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

Cs value................................................................................ 1nF to 200nF

Cx value...................................................................................0 to 100pF

4.3 AC SPECIFICATIONS

Vdd = 5.0, Ta = recommended

, Cx = 5pF, Cs = 39nF, Fosc = 10MHz

Including detection integratorms99Response timeT

Before all timings degradems5.50.1Allowable burst duration rangeT

BLMR

counts1,000Burst length, each channelN

ms3Burst duration, each channelT

ms33Burst spacing intervalT

µs1.6Transfer durationT

µs1.2Charge durationT

ms330Recalibration timeT

NotesUnitsMaxTypMinDescriptionParameter

4.4 DC SPECIFICATIONS

Vdd = 5.0V, Cs = 39nF, Cx = 5pF, Fosc = 10MHz, Ta = recommended range, unless otherwise noted

bits1410Acquisition resolutionA

OPT1, OPT2µA±1Input leakage currentI

OUTn, 1mA sourceVVdd-0.7High output voltageV

OUTn, 4mA sinkV0.6Low output voltageV

OPT1, OPT2V2High input logic levelV

OPT1, OPT2V0.7Low input logic levelV

Req’d for startup, w/o reset circuitV/s100Supply turn-on slopeV

DDS

mA82.5Supply currentI

NotesUnitsMaxTypMinDescriptionParameter

8 QT160/161 1.06/1102

4.5 SIGNAL PROCESSING

Option pin selectedsecs10, 60, infinitePost-detection recalibration timer duration

ms/level231Negative drift compensation rate

ms/level990Positive drift compensation rate

samples3Consensus filter length (Detection integrator)

counts2Hysteresis

counts6Threshold differential

NotesUnitsMaxTypMinDescription

All curves at Vdd = 5.0V

Figure 4-1 Figure 4-2

Figure 4-3

9 QT160/161 1.06/1102

Burst Duration vs. Cs, Cx

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 1020304050

Burst Duration, Microseconds

Cs = 220nF

Cs = 100nF

Cs = 47nF

Cs = 39nF

Cs = 22nF

Cs = 10nF

Burst Duration v s. Cs, Cx

500

1000

1500

2000

2500

3000

3500

4000

0 1020 304050

Burst Duration, Microseconds

Cs = 47nF

Cs = 39nF

Cs = 22nF

Cs = 10nF

Burst Duration cs. Cs, Cx

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 50 100 150 200 250

Cs, nF

Burst Duration, Microseconds

Cx = 5pF

Cx = 10pF

Cx = 15pF

Cx = 22pF

Cx = 33pF

Cx = 47pF

5 - PACKAGE OUTLINES

Typical0.0130.008Typical0.2030.203Y

0.390.329.9068.128x

0.310.317.8747.874Aa

0.180.1433.6323.632S1

0.1450.1253.6833.175S

-0.015-0.381r

0.140.1253.5563.175R

BSC0.10.1BSC2.542.54F

Typical0.0650.04Typical1.6511.016L1

4 places0.020.0084 places0.5080.203L

0.0220.0160.5590.406P

0.0480.0231.220.584Q

BSC1.31.3BSC33.0233.02m

1.3951.38535.17934.163M

0.330.318.3827.874A

0.2950.287.4937.112a

NotesMaxMinNotesMaxMin

InchesMillimeters

SYMBOL

Package type: 28-Pin Dual-In-Line

Base level

Seating level

0.0080.0020.210.050h

0.0780.0681.991.730H

8º0º8º0ºØ

0.0090.0050.220.130e

0.0370.0220.950.550E

0.0150.0100.380.250L

0.0260.0260.650.650D

0.2120.2055.385.2002a

0.3110.3017.97.650W

0.4070.39610.3310.070M

NotesMaxMinNotesMaxMin

InchesMillimeters

SYMBOL

Package type: 28-pin SSOP

10 QT160/161 1.06/1102

7 - PIN LISTINGS

Reset / recalibrate (active low)/RST28

Oscillator inputOSC_I27

Oscillator outputOSC_O26

Option input 2OPT225

Option input 1OPT124

Detection output 6 (active high)OUT623

Detection output 5 (active high)OUT522

Detection output 4 (active high)OUT421

Detection output 3 (active high)OUT320

Detection output 2 (active high)OUT219

Detection output 1 (active high)OUT118

Channel 6 sense pin BSNS6B17

Channel 6 sense pin A to keySNS6A16

Channel 5 sense pin BSNS5B15

Negative power (Ground)Vss14

Channel 5 pin A to keySNS5A13

Channel 4 pin BSNS4B12

Channel 4 pin A to keySNS4A11

Channel 3 pin BSNS3B10

Channel 3 pin A to keySNS3A9

Channel 2 pin BSNS2B8

Channel 2 pin A to keySNS2A7

Channel 1 pin BSNS1B6

Channel 1 pin A to keySNS1A5

Positive powerVdd4

Positive powerVdd3

Negative power (Ground)Vss2

Negative power (Ground)Vss1

FunctionNamePin

Table 7-2 Pin Descriptions - QT160-AS

Reset / recalibrate (active low)/RST28

Oscillator inputOSC_I27

Oscillator outputOSC_O26

Option input 2OPT225

Option input 1OPT124

Detection output 6 (active high)OUT623

Detection output 5 (active high)OUT522

Detection output 4 (active high)OUT421

Detection output 3 (active high)OUT320

Detection output 2 (active high)OUT219

Detection output 1 (active high)OUT118

Channel 6 pin BSNS6B17

Channel 6 pin A to keySNS6A16

Channel 5 pin BSNS5B15

Channel 5 pin A to keySNS5A14

Channel 4 pin BSNS4B13

Channel 4 pin A to keySNS4A12

Channel 3 pin BSNS3B11

Channel 3 pin A to keySNS3A10

Channel 2 pin BSNS2B9

Channel 2 pin A to keySNS2A8

Channel 1 pin BSNS1B7

Channel 1 pin A to keySNS1A6

Negative power (Ground)Vss5

Negative power (Ground)Vss4

Negative power (Ground)Vss3

Positive powerVdd2

Positive powerVdd1

FunctionNamePin

Table 7-1 Pin Descriptions - QT160-D

8 - ORDERING INFORMATION

QT161-ASSOP-28-40 - 105CQT161-AS

QT161PDIP-280 - 70CQT161-D

QT160-ASSOP-28-40 - 105CQT160-AS

QT160PDIP-280 - 70CQT160-D

MARKINGPACKAGETEMP RANGEPART

11 QT160/161 1.06/1102

Patented and patents pending

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Tel: 412-391-7367 Fax: 412-291-1015

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

to our Terms and Conditions of sale and supply of services which are available online at www.qprox.com and are supplied with every order

acknowledgment. QProx, QTouch, QMatrix, QLevel, and QSlide are trademarks of QRG. QRG products are not suitable for medical

(including life-saving equipment), safety or mission critical applications or other similar purposes. Except as expressly set out in QRG's

Terms and Conditions, no licenses to patents or other intellectual property of QRG (express or implied) are granted by QRG in connection

with the sale of QRG products or provision of QRG services. QRG will not be liable for customer product design and customers are entirely

responsible for their products and applications which incorporate QRG's products.