QT113H-ISG Datasheet QT113H-IS, QT113H-S, QT113-D | P4-P6

4-1 to 4-3). The value of Cs also has a dramatic effect on

sensitivity, and this can be increased in value (up to a limit).

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.

1.3.5.2 Decreasing Sensitivity

In some cases the QT113 may be too sensitive, even on low

gain. In this case gain can be lowered further by a number of

strategies: making the electrode smaller, making the

electrode into a sparse mesh using a high

space-to-conductor ratio (Figure 1-3), or by decreasing Cs.

2 - QT113 SPECIFICS

2.1 SIGNAL PROCESSING

The QT113 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 numerous adverse environmental

changes.

2.1.1 D

RIFT

OMPENSATION

LGORITHM

Signal drift can occur because of changes in Cx

and Cs over time. It is crucial that drift be

compensated for, otherwise false detections,

non-detections, and sensitivity shifts will follow.

Drift compensation (Figure 2-1) 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 QT113 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 QT113'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 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.

Note that the positive and negative drift

compensation rates are different.

2.1.2 T

HRESHOLD

ALCULATION

Unlike the QT110 device, the internal threshold level is fixed

at one of two setting as determined by Table 1-1. These

setting are fixed with respect to the internal reference level,

which in turn can move in accordance with the drift

compensation mechanism..

The QT113 employs a hysteresis dropout below the

threshold level of 17% of the delta between the reference and

threshold levels.

2.1.3 M

-D

URATION

If an object or material obstructs the sense pad the signal

may rise enough to create a detection, preventing further

- 4 -

Figure 1-5

Shielding Against Fringe Fields

Sense

wire

Sense

wire

Unshielded

Electrode

Shielded

Electrode

Figure 2-1 Drift Compensation

Threshold

Signal

Hysteresis

Reference

Output

Vss (Gnd)

Low - 12 counts

Vdd

High - 6 counts

Tie Pin 5 to:Gain

Table 1-1 Gain Setting Strap Options

operation. To prevent this, the sensor includes a timer which

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 will once again

function normally, even if partially or fully obstructed, to the

best of its ability given electrode conditions. There are two

finite timeout durations available via strap option: 10 and 60

seconds (Table 2-1).

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 QT113 incorporates 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 QT113, 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

The QT113 has no recalibration pin; a forced recalibration is

accomplished only when the device is powered up. However,

supply drain is low so it is a simple matter to treat the entire

IC as a controllable load; simply driving the QT113's Vdd pin

directly from another logic gate or a microcontroller port

(Figure 2-2) 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. Note

that most 8051-based micros have only a weak pullup drive

capability and will require CMOS buffering. 74HC or 74AC

series gates can directly power the QT113, as can most other

microcontrollers.

Option strap configurations are read by the QT113 only on

powerup. Configurations can only be changed by powering

the QT113 down and back up again; again, a microcontroller

can directly alter most of the configurations and cycle power

to put them in effect.

2.1.6 R

ESPONSE

IME

The QT113's response time is highly dependent on burst

length, which in turn is dependent on Cs and Cx (see Figures

4-1, 4-2). With increasing Cs, response time slows, while

increasing levels of Cs reduce response time. Figure 4-3

shows the typical effects of Cs and Cx on response time.

2.2 OUTPUT FEATURES

The QT113 is 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 output of the QT113 can respond in a DC mode, where

the output is active-low upon detection. The output will

remain active-low 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.

In this mode, three Max On-Duration timeouts are available:

10 seconds, 60 seconds, and infinite.

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.

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 H

EART

EAT

™ O

UTPUT

The QT113 output has a full-time HeartBeat™ ‘health’

indicator superimposed on it. This operates by taking 'Out'

into a 3-state mode for 300µs once after 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 pulldown

resistor on Out, and feeding the resulting negative-going

pulse into a counter, flip flop, one-shot, or other circuit. Since

Out is normally high, a pulldown resistor will create negative

HeartBeat pulses (Figure 2-3) when the sensor is not

detecting an object; when detecting an object, the output will

remain low for the duration of the detection, and no

HeartBeat pulse will be evident.

If the sensor is wired to a microcontroller as shown in Figure

2-4, the microcontroller can reconfigure the load resistor to

either ground or Vcc depending on the output state of the

QT113, so that the pulses are evident in either state.

- 5 -

infiniteVddGnd

DC Out

10sGndGnd

Toggle

60sGndVdd

DC Out

10sVddVdd

DC Out

Max On-

Duration

Tie

Pin 4 to:

Tie

Pin 3 to:

Table 2-1 Output Mode Strap Options

Figure 2-2 Powering From a CMOS Port Pin

0.01µF

CMOS

microcontroller

OUT

PORT X.m

PORT X.n

Vdd

Vss

QT110

Electromechanical devices like relays will usually ignore this

short pulse. The pulse also has too low a duty cycle to visibly

affect LED’s. It can be filtered completely if desired, by

adding an RC timeconstant to filter the output, or if interfacing

directly and only to a high-impedance CMOS input, by doing

nothing or at most adding a small non-critical capacitor from

Out to ground (Figure 2-5).

The QT113H variant has an active-high output; the heartbeat

signal of the QT113H works in exactly the same manner.

2.2.4 O

UTPUT

RIVE

The QT113’s `output is active low and can sink up to 5mA of

non-inductive current. If an inductive load is used, such as a

small relay, the load should be diode clamped to prevent

damage. When set to operate in a proximity mode (at high

gain) the current 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.

Care should be taken when the QT113 and the load are both

powered from the same supply, and the supply is minimally

regulated. The QT113 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

output 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

Out is active.

The output of the QT113 can directly drive a resistively

limited LED. The LED should be connected with its cathode

to the output and its anode towards Vcc, so that it lights when

the sensor is active. If desired the LED can be connected

from Out to ground, and driven on when the sensor is

inactive.

The QT113H variant has an active-high output.

3 - CIRCUIT GUIDELINES

3.1 SAMPLE CAPACITOR

Charge sampler Cs can be virtually any plastic film or

medium-K ceramic capacitor. The acceptable Cs range is

from 10nF to 500nF depending on the sensitivity required;

larger values of Cs demand higher stability to ensure reliable

sensing. Acceptable capacitor types include polycarbonate,

PPS film, or NPO/C0G ceramic.

3.2 OPTION STRAPPING

The option pins Opt1 and Opt2 should never be left floating.

If they are floated, the device will draw excess power and the

options will not be properly read on powerup. Intentionally,

there are no pullup resistors on these lines, since pullup

resistors add to power drain if tied low.

The Gain input should be connected to either Vdd or Gnd.

Tables 1-1 and 2-1 show the option strap configurations

available.

3.4 POWER SUPPLY, PCB LAYOUT

The power supply can range from 2.5 to 5.0 volts. At 3 volts

current drain averages less than 600µA in most cases, but

can be higher if Cs is large. Increasing Cx values will actually

decrease power drain. Operation can be from batteries, but

be cautious about loads causing supply droop (see Output

Drive, previous section).

As battery voltage sags with use or fluctuates slowly with

temperature, the QT113 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

- 6 -

Figure 2-4

Using a micro to obtain HB pulses in either output state

Figure 2-3

Getting HearBeat pulses with a pull-down resistor

+2.5 to 5

OUT

OPT1

OPT2

GAIN

SNS1

SNS2

Vss

Vdd

HeartBeat™ Pulses

Microcontroller

PORT_M.x

PORT_M.y

OUT

OPT1

OPT2

GAIN

SNS1

SNS2

Figure 2-5 Eliminating HB Pulses

OUT

OPT1

OPT2

GAIN

SNS1

SNS2

CMOS

100pF

GATE OR

MICRO INPUT

P1-P3 P4-P6 P7-P9 P10-P12

QT113H-ISG

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