QT310-IS - Atmel - Product.Network

ROX

™

QT310

PRELIMINARY

SER

ROGRAMMABLE

DVANCED

ENSOR

Single channel digital advanced capacitive sensor IC

Full autocal capability

User programmable via cloning process

Internal eeprom storage of user setups, cal data



Variable drift compensation

Variable recalibration timeouts

BG and OBJ cal modes for learn-by-example



Sync pins for daisy-chaining or noise suppression



Variable gain via Cs capacitor change



Selectable output polarity, high or low

Toggle mode (optional via setups)



Push-pull output

Completely programmable output behavior

via cloning process from a PC

HeartBeat™ health indicator (can be disabled)

APPLICATIONS

Material detection

Toys & games

Access controls

Microswitch replacement

Appliance controls

Security systems

Fluid level sensors

Industrial panels

The QT310 charge-transfer (“QT’”) touch sensor IC is a self-contained digital IC capable of detecting proximity, touch, or fluid

level when connected to a corresponding type of electrode. It projects sense fields through almost any dielectric, like glass,

plastic, stone, ceramic, and wood. It can also turn metal-bearing objects into intrinsic sensors, making them respond to

proximity or touch. This capability coupled with its ability to self calibrate continuously or to have fixed calibration by example

can lead to entirely new product concepts.

It is designed specifically for advanced human interfaces like control panels and appliances or anywhere a mechanical switch

or button may be found; it can also be used for material sensing and control applications, and for point-level fluid sensing.

The ability to daisy-chain the ICs permits the construction of high-sensitivity controls where the electrodes of two or more

QT310’s are adjacent to each other.

The burst rate can be programmed to a wide variety of settings, allowing the designer to trade off power consumption for

response time. The device requires only a common inexpensive external capacitor.

The IC’s RISC core employs 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. All key operating parameters can

be set by the designer via the internal eeprom which can be configured via Quantum’s cloning process to alter sensitivity, drift

compensation rate, max on-duration, output polarity, calibration mode, Heartbeat™ feature, and toggle mode.

No external switches, opamps, or other analog components aside from Cs are required.

The Quantum-pioneered HeartBeat™ signal is also included, allowing a host controller to monitor the health of the QT320

continuously if desired. By using the charge transfer principle, the IC delivers a level of performance clearly superior to older

technologies in a highly cost-effective package.

-QT310-IS-40

C to +85

QT310-D-0

C to +70

8-PIN DIPSOICT

AVAILABLE OPTIONS

Serial clone data inSDI7

Serial clone data outSDO6

Serial clone data clockSCK3

Alternate Pin Functions for Cloning

Positive supplyVDD8

Detection outputOUT7

Sync Input/SYNC_I6

Sense 2 lineSNS25

Negative supply (ground)VSS4

Sense 1 lineSNS13

Sync Output/SYNC_O2

Ext Cal, latch clear input/CAL_CLR1

FunctionNamePin

Table 1-1 Pin Descriptions

1 - OVERVIEW

The QT310 is a digital burst mode charge-transfer (QT)

sensor designed for touch controls, level sensing and

proximity sensing; it includes all hardware and signal

processing functions necessary to provide stable sensing

under a wide variety of changing conditions. Only two low

cost, non-critical capacitor are required for operation.

A unique aspect of the QT310 is the ability of the designer to

‘clone’ a wide range of user-defined setups into the part’s

eeprom during development and in production. Cloned setups

can dramatically alter the behavior of the part. For production,

the parts can be cloned in-circuit or can be procured from

Quantum pre-cloned.

Figure 1-1 shows the basic QT310 circuit using the device,

with a conventional output drive and power supply

connections.

1.1 BASIC OPERATION

The QT310 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

several consecutive confirmations of a detection before the

output is activated.

A unique cloning process allows the internal eeprom of the

device to be programmed to permit unique combinations of

sensing and processing functions.

1.2 ELECTRODE DRIVE

1.2.1 S

WITCHING

PERATION

The IC implements direct-to-digital capacitance acquisition

using the charge-transfer method, in a process that is better

understood as a capacitance-to-digital converter (CDC). The

QT switches and charge measurement functions are all

internal to the IC (Figure 1-2).

The CDC treats sampling capacitor Cs as a floating store of

accumulated charge which is switched between the sense

pins; as a result, the sense electrode can be connected to

either pin with no performance difference. In both cases the

rule Cs >> Cx must be observed for proper operation. The

polarity of the charge build-up across Cs during a burst is the

same in either case. Typical values of Cs range from 1nF to

200nF for touch operation.

Larger values of Cx cause charge to be transferred into Cs

more rapidly, reducing available resolution and resulting in

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

differential voltage across it, increasing available resolution

and raising gain. The value of Cs can thus be increased to

allow larger values of Cx to be tolerated (Figures 5-1 to 5-2).

As Cx increases, the length of the burst decreases resulting in

lower signal numbers.

It is possible to connect separate Cx and Cx’ loads to SNS1

and SNS2 simultaneously, although the result is no different

than if the loads were connected together at SNS1 (or SNS2).

It is important to limit the amount of stray Cx capacitance on

both terminals, especially if the load Cx is already large. This

can be accomplished by minimising trace lengths and widths.

2 QT310/R1.01 07/02

Figure 1-2 Internal Switching

Burst Controller

Single-Slope

Switched Capacitor ADC

Charge

Amp

Cs Cx

SNS1

SNS2

Result

Start

Done

Figure 1-1 Basic QT310 circuit

ELECTRODE

4.7nF

to 5

SYNC_O

OUT SNS2

SNS1

VDD

SYNC_I

/CAL

VSS

1.2.2 C

ONNECTION

LECTRODE

The PCB traces, wiring, and any components associated with

or in contact with SNS1 and SNS2 will become touch

sensitive and should be treated with caution to limit the touch

area to the desired location.

Multiple electrodes can be connected, 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

electrodes.

1.2.3 B

URST

ODE

PERATION

The acquisition process occurs in bursts (Figure 1-7) of

variable length, in accordance with the single-slope CDC

method. The burst length depends on the values of Cs and

Cx. Longer burst lengths result in higher gains and more

sensitivity for a given threshold setting, but consume more

average power and are slower.

Burst mode operation acts to lower average power while

providing a great deal of signal averaging inherent in the CDC

process, making the signal acquisition process more robust.

The QT method is a very low impedance method of sensing

as it loads Cx directly into a very large capacitor (Cs). This

results in very low levels of RF susceptibility.

1.3 ELECTRODE DESIGN

1.3.1 E

LECTRODE

EOMETRY

AND

IZE

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

cases common sense and a little experimentation can result

in a good electrode design. The QT310 will operate equally

well with a long, thin electrode as with a round or square one;

even random shapes are acceptable. The electrode can also

be a 3-dimensional surface or object. Sensitivity is related to

electrode surface area, orientation with respect to the object

being sensed, object composition, and the ground coupling

quality of both the sensor circuit and the sensed object.

Smaller electrodes have less sensitivity than large ones.

If a relatively large electrode surfaces are desired, and if tests

show that an electrode has a high Cx capacitance that

reduces the sensitivity or prevents proper operation, the

electrode can be made into a mesh (Figure 1-3) which will

have a lower Cx than a solid electrode area.

1.3.2 K

IRCHOFF

’

URRENT

Like all capacitance sensors, the QT310 relies on Kirchoff’s

Current Law (Figure 1-4) 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.

The implications of Kirchoff’s law can be most visibly

demonstrated by observing the E3B eval board’s sensitivity

change between laying the board on a table versus holding

the board in your hand by it’s batteries. The effect can also be

observed by holding the board by the electrode ‘Sensor1’,

letting it recalibrate, then touching the battery end; the board

will work quite well in this mode.

1.3.3 V

IRTUAL

APACITIVE

ROUNDS

When detecting human contact (e.g. a fingertip), grounding of

the person is never required, nor is it necessary to touch an

exposed metal electrode. The human body naturally has

several hundred picofarads of ‘free space’ capacitance to the

local environment (Cx3 in Figure 1-4), which is more than two

orders of magnitude greater than that required to create a

return path to the QT310 via earth. The QT310's PCB

however can be physically quite small, so there may be little

‘free space’ coupling (Cx1 in Figure 1-4) between it and the

environment to complete the return path. If the QT310 circuit

ground cannot be grounded via the supply connections, then

a ‘virtual capacitive ground’ may be required to increase

return coupling.

3 QT310/R1.01 07/02

Figure 1-3 Mesh Electrode Geometry

Figure 1-4 Kirchoff’s Current Law

A ‘virtual capacitive ground’ can be created by connecting the

QT310’s own circuit ground to:

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

(2) A floating conductive ground plane;

(3) A fastener to a supporting structure;

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

connected anyway).

Because the QT310 operates at a relatively low frequency,

about 500kHz, even long inductive wiring back to ground will

usually work fine.

Free-floating ground planes such as metal foils should

maximise 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.

1.3.4 F

IELD

HAPING

The electrode can be prevented from sensing in undesired

directions with the assistance of metal shielding connected to

circuit ground (Figure 1-5). 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 QT310, 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.

1.4 SENSITIVITY ADJUSTMENTS

There are three variables which influence sensitivity:

1. Cs (sampling capacitor)

2. Cx (unknown capacitance)

3. Signal threshold value

There is also a sensitivity dependence of the whole device on

Vdd. Cs and Cx effects are covered in Section 1.2.1.

The threshold setting can be adjusted independently from 1 to

255 counts of signal swing (Section 2.3).

Note that sensitivity is also a function of other things like

electrode size, 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 mutual coupling of the sensor circuit and the object (usually

via the local environment, or an actual galvanic connection).

Threshold levels of less than 5 counts in BG mode are not

advised; if this is the case, raise Cs so that the threshold can

also be increased.

1.4.1 I

NCREASING

ENSITIVITY

In some cases it may be desirable to greatly increase

sensitivity, for example when using the sensor with very thick

panels having a low dielectric constant, or when sensing low

capacitance objects.

Sensitivity can be increased by using a bigger electrode,

reducing panel thickness, or altering panel composition.

Increasing electrode size can have diminishing returns, as

high values of Cx load will also reduce sensor gain (Figures

5-1 and 5-2). The value of Cs also has a dramatic effect on

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

Increasing electrode surface area will not substantially

increase sensitivity if its area is already larger than the object

to be detected. The panel or other intervening material can be

made thinner, but again there are diminishing rewards for

4 QT310/R1.01 07/02

Figure 1-5 Shielding Against Fringe Fields

Figure 1-6 Burst Detail

doing so. Panel material can also be changed to one having a

higher dielectric constant, which will help propagate the field.

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 electrically conductive.

1.4.2 D

ECREASING

ENSITIVITY

In some cases the circuit may be too sensitive, even with high

signal threshold values. In this case gain can be lowered by

making the electrode smaller, using sparse mesh with a high

space-to-conductor ratio (Figure 1-3), and most importantly by

decreasing Cs. Adding Cx capacitance will also decrease

sensitivity.

It is also possible to reduce sensitivity by making a capacitive

divider with Cx by adding a low-value capacitor in series with

the electrode wire.

1.5 TIMING

Figure 1-7 and 1-8 shows the basic timing parameters of the

QT310. The basic QT310 timing parameters are:

Ti Basic timing interval (1.5.1)

Tbs Burst spacing (1.5.1)

Tbd Burst duration (1.5.2)

Tmod Max On-Duration (1.5.3)

Tdet Detection response time (1.5.4)

1.5.1 B

URST

PACING

: T

, SC, T

Between acquisition bursts, the device can go into a low

power sleep mode. The percentage of time spent in sleep

depends on the burst spacing and the burst length; if the burst

length occupies all of the sleep interval, no time will be spent

in sleep mode and the part will operate at maximum power

drain.

The burst spacing is a multiple of the basic timing interval Ti;

Ti in turn depends heavily on Vdd (see Section 2.1 and Figure

5-4). The parameter ‘Sleep Cycles’ or SC is the user-defined

Setup value which controls how many Ti intervals there are

from the start of a burst until the start of the next such burst.

The resulting timing is Tbs:

Tbs = SC x Ti where SC > 0

All the basic timing parameters of the QT310 such as

recalibration delay etc. are dependent on Tbs.

If SC = 0, the device never sleeps between bursts (Figure

1-8). This mode is fast but consumes maximum power; it is

also unregulated in timing from burst to burst, depending on

the burst lengths.

Conversely if SC >> 0, the device will spend most of its time

in sleep mode and will consume very little power, but it will be

slower to respond.

By selecting a supply voltage and a value for SC, it is possible

to fine-tune the circuit for the desired speed / power trade-off.

1.5.2 B

URST

URATIONS

: T

The burst duration depends entirely on the values of Cs and

Cx, and to a lesser extend, Vdd. The burst is composed of

hundreds of charge-transfer cycles (Figure 1-6) operating at

about 250kHz.

When SC=0 (no sleep cycles), the sensor operates without a

fixed timing and the acquisition spacing Tbs is the sum of the

burst durations plus the signal processing time, which is about

300us (Figure 1-8). In this mode of operation, Tbs and Tbd

are nearly the same value.

1.5.3 M

-D

URATION

, T

MOD

The Max On-Duration is the amount of time required for

sensor to recalibrate itself when continuously detecting. This

parameter is user settable by changing MOD and SC (Section

2.6).

Tmod restarts if the sensor becomes inactive before the end

of the Max On Duration period.

5 QT310/R1.01 07/02

Figure 1-7 Burst when SC is set to 1

(Observed using a 750K resistor in series with probe) Figure 1-8 Burst when SC is set to 0 (no sleep cycles)

(

Observed usin

a 750K resistor in series with

robe

)

1.5.4 R

ESPONSE

IME

, T

DET

Response time from the onset of detection to the OUT pin

becoming active depends on:

Ti Basic Timing Interval

SC Sleep Cycles (user setting)

DIT Detection Integrator Target (user setting)

DIS Detect Integration Speed (user setting)

Tbd Burst duration (if DIS is set too fast)

Ti depends in turn on Vdd.

If the control bit DIS is normal (0), then Tdet depends on the

rate at which the bursts are acquiring, and the value of DIT. A

DIT number of bursts must confirm the detection before the

OUT line becomes active:

Tdet = SC x Ti x DIT (normal DIS)

If DIS is set to fast, then Tdet also depends on BL:

Tdet = (SC x Ti) + (DIT-1)*Tbd (fast DIS)

Ti depends in turn on Vdd; Tbd depends on Cs and Cx.

Quantum’s QT3View software calculates an estimate of

response time based on these parameters.

1.6 EXTERNAL RECALIBRATION

The /CAL_CLR pin can be used to recalibrate the sensor on

demand. A low pulse of at least Tbs (burst spacing) duration

is require to initiate a recalibration. The calibration occurs just

after /CAL_CLR returns high.

In BG1 mode (Section 2.8.4), the calibration data is not stored

in EEPROM, and the part will recalibrate after each power up.

In BG1 mode, if the device has been set for Toggle Latch

output mode, the /CAL_CLR pin becomes an output reset

control and the part cannot be recalibrated via /CAL_CLR.

However the part can be recalibrated by powering it down and

back up again (Section 2.7.3).

In BG2 mode, the calibration data is stored in EEPROM, and

the part will not recalibrate after power up, using instead the

stored calibration data. The internal eeprom has a life

expectancy of 100,000 erase/write cycles.

In OBJ mode, the part stores the calibration data into

EEPROM and the part will not recalibrate after power up,

using instead the stored calibration data.

In both BG2 and OBJ mode, the device must be calibrated

using the /CAL_CLR input, or the calibration data can be set

via cloning process, otherwise the calibration data

will be invalid.

2 - Control & Processing

All acquisition functions are digitally controlled and

can be altered via the cloning process.

Signals are processed using 16 bit integers, using

Quantum-pioneered algorithms specifically

designed to provide for high survivability.

2.1 SLEEP CYCLES (SC)

Range: 0..255; Default: 1

Affects speed & power of entire device.

Refer to Section 1.5.1 for more information on the effect of

Sleep Cycles.

SC changes the number of intervals Ti separating two

consecutive burst (Figure 1-7 and 1-8). SC = 0 disables sleep

intervals and bursts are crowded together with a rep rate that

depends entirely on the burst lengths (Section 1.5.2).

Response time, drift compensation rate, max on-duration, and

power consumption are all affected by this parameter. A high

value of SC will make the sensor very low power and very

slow.

2.2 DRIFT COMPENSATION (PDC, NDC)

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

electrode contamination and ageing effects. It is important to

compensate for drift, otherwise false detections and sensitivity

shifts can occur.

Drift compensation is performed by making the signal’s

reference level slowly track the raw signal while no detection

is in effect. The rate of adjustment must be performed slowly,

otherwise legitimate detections could be affected. The device

compensates using a slew-rate limited change to the signal

reference level; the threshold and hysteresis points are slaved

to this reference.

Once an object is detected, drift compensation stops since a

legitimate signal should not cause the reference to change.

Positive and negative drift compensation rates (PDC, NDC)

can be set to different values (Figure 2-1). This is invaluable

for permitting a more rapid reference recovery after the device

has recalibrated while an object was present and then

removed.

Positive drift occurs when the Cx slowly increases. Negative

drift occurs when Cx slowly decreases (see Section 2.8.1).

If SC > 0, then PDC+1 sets the number of burst spacings,

Tbs, that determines the interval of drift compensation, where:

Tbs = SC x Ti (Section 1.5.1)

Example: PDC = 9, (user setting)

Tbs = 100ms

then

Tpdc = (9+1) x 100ms = 1 sec

6 QT310/R1.01 07/02

Figure 2-1 Drift Compensation

If SC = 0, the result is multiplied by 16, and Tbd becomes the

time basis for the compensation rate, where:

Tbd = Tbs (Section 1.5.2)

Example: PDC = 5, (user setting)

Tbd = 15ms

then

Tpdc = (5+1) x 15ms x 16 = 1.44 sec

NDC operates in exactly the same way as PDC.

2.2.1 N

EGATIVE

RIFT

OMPENSATION

(NDC)

Range: 0..255; Default: 2; 255 disables

Compensation for drift with increasing internal signals, or

decreasing Cx

NDC corrects the reference when the internal signal is drifting

up, i.e. Cx is decreasing (see Section 2.8.1). Every interval of

time the device checks for the need to move its reference

level in the positive internal direction (negative Cx direction) in

accordance with signal drift. The resulting timing interval for

this adjustment is Tndc.

This should normally be faster than positive drift

compensation in order to compensate quickly for the removal

of a touch or obstruction from the electrode after a MOD

recalibration (Section 1.5.3).

2.2.2 P

OSITIVE

RIFT

OMPENSATION

(PDC)

Range: 0...255 Default: 100; 255 disables

Compensation for drift with decreasing internal signals,

or increasing Cx

This corrects the reference when the signal drifting down, i.e.

Cx is increasing (see Section 2.8.1). Every interval of time the

device checks for the need to move its reference level in the

negative internal direction (positive Cx direction) in

accordance with signal drift. The resulting timing interval for

this adjustment is Tpdc.

This value should not be set too fast, since an approaching

finger could be compensated for partially or entirely before

even touching the sense electrode.

2.3 THRESHOLD (THR)

Range: 1..255; Default: 6

Affects sensitivity; not used in OBJ

mode.

The detection threshold is measured in

terms of counts of signal deviation with

respect to the reference level. Higher

threshold counts equate to less sensitivity

since the signal must travel further in order

to cross the detection point.

If the signal equals or exceeds the threshold

value, a detection can occur. The detection

will end only when the signal become less

than the hysteresis level.

THR is not used in OBJ mode (Section

2.8.5). In OBJ mode the threshold is set by

example during calibration.

2.4 HYSTERESIS (HYS)

Range: 0...255; Default: 2; 0 disables

Affects detection stability.

Hysteresis is measured in terms of counts of signal deviation

relative to the threshold level. Higher values equate to more

hysteresis. The device will become inactive after a detection

when the Cx level moves below THR-HYS in normal mode or

above THR+HYS in absence mode (Section2.8.2) Hysteresis

helps prevents chattering of the OUT pin.

If HYS is set to a value equal or greater than THR, the device

may malfunction. Hysteresis should be set to between 10%

and 40% of the threshold value for best results.

If HYS is set to 0, hysteresis will not be used.

If THR = 10 and HYS = 2, the hysteresis zone will represent

20% of the threshold level. In this example the ‘hysteresis

zone’ is the region from 8 to 10 counts of signal level. Only

when the signal falls back to 7 will the OUT pin become

inactive.

2.5 DETECT INTEGRATORS (DIA, DIB, DIS)

DIAT Range: 1..256 Default: 10

DIBT Range: 1..256 Default: 10

DIS Range: 0, 1 Default: 1

Affects response time Tdet.

See Figure 2-2 for operation.

It is usually desirable to suppress detections generated by

sporadic electrical noise or from quick contact with an object.

To accomplish this, the QT310 incorporates a pair of

detection integrator (‘DI’) counters that serve to filter out

sporadic noise. These counters can also have the effect of

slowing down response time if desired.

DIA / DIAT: The first counter, DIA, increments after each

burst if the signal threshold has been exceeded, until DIA

reaches its terminal count DIAT, after which the OUT pin is

activated. If the signal falls below the threshold level prior to

reaching DIAT, DIA is immediately reset to zero.

7 QT310/R1.01 07/02

Figure 2-2 Detect Integrators Operation (Positive mode, Section 2.8.2)

DIA can also be viewed as a 'consensus' filter that requires

signal threshold crossings over ‘T’ successive bursts to create

an output, where ‘T’ is the terminal count (DIAT).

DIB / DIBT: If OUT has been active and the signal falls below

the hysteresis level, a second detection integrator, DIB,

counts up.

When DIBT is reached, OUT is deactivated.

DISA / DISB: Because the DI counters count at the burst rate,

slow burst spacings can result in very long detection delays

with terminal counts above 1. To cure this problem, the burst

rate can be made faster while DIA or DIB are counting. This

creates the effect of a gear-shifted detection process: normal

speed when there are no threshold crossings, and fast mode

when a detection is pending.

DISA and DISB respectively gearshift the effect of DIA and

DIB. The gear-shifting ceases and normal speed resumes

once the detection is confirmed (DIA = DIAT) and once the

detection ceases (DIB = DIBT).

When SC=0 the device operates without any sleep cycles,

and so the timebase for the DI counters is very fast.

2.6 MAX ON-DURATION (MOD)

Range: 0..255; Default: 14; 255 disables

Affects parameter Tmod, the calibration delay time

If a stray object remains on or near the sense electrode, the

signal may rise enough to activate the OUT pin thus

preventing normal operation. To provide a way around this, a

Max On-Duration (‘MOD’) timer is provided to cause a

recalibration if the activation lasts longer than the designated

timeout, Tmod.

The MOD function can also be disabled, in which case the

sensor will never recalibrate unless the part is powered down

and back up again. In infinite timeout the designer should take

care to ensure that drift in Cs, Cx, and Vdd do not cause the

device to ‘stick on’ inadvertently when the target object is

removed from the sense field.

MOD is expressed in multiples of the burst space interval,

which can be either Tbs or Tbd depending on the Sleep

Cycles setting (SC).

If SC > 0, the delay is:

Tmod = (MOD + 1) x 16 x Tbs

Example:

Tbs = 100ms,

MOD = 9;

Tmod = (9 + 1) x 16 x 100ms = 160 secs.

If SC = 0, Tmod is a function of the total combined burst

durations, Tbd. If SC = 0, the delay is:

Tmod = (MOD + 1) x 256 x Tbd

Example:

Tbd = 18ms,

MOD = 9;

Tmod = (9 + 1) x 256 x 18ms = 46 secs.

If MOD = 255, recalibration timeout = infinite (disabled)

regardless of SC.

An MOD induced recalibration will make the OUT pin inactive

except if the output is set to toggle mode (Section 2.7.2), in

which case the OUT state will be unaffected but the sensor

will have recalibrated.

2.7 OUTPUT FEATURES

Available output processing options accommodate most

requirements; these can be set via the clone process.

If TOG and TOGL modes are disabled, OUT responds to

detections with a steady-state active logic level which lasts for

the duration of a detection, until a MOD timeout occurs

(Section 2.6).

The OUT pin is push-pull CMOS.

2.7.1 P

OLARITY

(OUTP)

Options: active-low or -high; Default: active-low

The polarity of OUT can be set via option OUTP using the

cloning process. Either active-low or active-high can be

selected. This not the same as ‘direction of signal detection’

(Section 2.8.1).

In ‘active high’ mode the normal, inactive polarity of OUT is

low; in ‘active low’ mode the normal, inactive polarity of OUT

is high.

OUTP also selects the initial state of OUT when the sensor is

used in Toggle or Toggle Latch modes (Sections 2.7.2, 2.7.3);

for example, if OUTP is set active-low, the initial state of OUT

after power-up will be high.

2.7.2 T

OGGLE

ODE

(TOG)

Options: enabled or disabled; Default: disabled

Toggle mode gives the OUT pin a touch-on / touch-off flip-flop

action, so that its state changes with each new detection. It is

most useful for controlling power loads, for example kitchen

appliances, power tools, light switches, etc.

MOD time-outs (Section 2.6) and the /CAL_CLR pin will

recalibrate the sensor but leave the OUT state unchanged.

The OUTP option (Section 2.7.1) sets the initial state of the

sensor after power-up.

2.7.3 T

OGGLE

ATCH

ODE

(TOGL)

Options: enabled or disabled; Default: disabled

In this mode, OUT becomes active when a valid detection

occurs but will only go inactive again if an external clear signal

is applied to the part; further detections after the first one will

not change the state of OUT.

The external clear signal is applied to the

/CAL_CLR

which functions only as latch clear input if TOGL is enabled.

The only way to recalibrate the sensor externally in TOGL

mode is to cycle power off and back on.

A logic low pulse on

/CAL_CLR

will clear the latch and make

OUT inactive. As the

/CAL_CLR

pin is sampled once per

burst, the clear pulse has to be at least as long as Tbs (the

burst duration) to ensure the latch clears.

If any underlying threshold detection remains active for longer

than the Max On-Duration (MOD) period the device will

recalibrate automatically, but the OUT pin will not change

state.

8 QT310/R1.01 07/02

A clear pulse applied to

/CAL_CLR

will clear the latch even if

the part is in the process of recalibrating due to a MOD

timeout.

The clear state of OUT can be set via the OUTP option

(Section 2.7.1).

Toggle Latch Mode cannot be used with BG2 or OBJ modes,

/CAL_

CLR must be used as a calibrate input in these two

modes (Sections 1.6, 2.8.4, 2.8.5).

2.7.4 H

EART

EAT

™ O

UTPUT

(HB)

Setup: Enable/Disable; Default: Enabled

The OUT pin has HeartBeat™ ‘health’ indicator pulses

superimposed on it. This operates by floating the 'OUT' pin for

approximately 15µs before each burst.

This pulse can be used to determine if the sensor is operating

properly. The frequency of the pulses can be used to

determine if the IC is operating within desired limits. The

Heartbeat signal can be tested by connecting a 10K resistor

to OUT that is toggled by a microcontroller depending on the

logic level of OUT.

Heartbeat pulses can be removed simply by placing a 100pF

capacitor on the OUT pin; if OUT is loaded into a high-

impedance CMOS input, this is usually enough.

It is possible to disable HeartBeat provided SC is set to zero,

by setting the HB control bit to '1'.

2.7.5 O

UTPUT

RIVE

APABILITY

The OUT pin is a push-pull CMOS type.

OUT can source or sink up to 2mA of non-inductive current. If

an inductive load is used, such as a small relay, the load

should be diode-clamped to prevent damage. The current

must be limited to 2mA max continuous to prevent detection

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.

2.8 DETECTION MODES

SD - Sense Direction: Pos or Neg; Default: Positive

DM - Detect Mode: BG or OBJ; Default: BG

BG - BG Mode: BG1 or BG2; Default: BG1

It is possible to change the basic way the device detects and

operates via the cloning process as described below. In

particular, it is possible to determine whether the device

responds to increases in Cx (‘normal’ detection) or decreases

in Cx (‘absence’ detection). It is also possible to change how

the device calibrates itself, in one of three possible modes.

2.8.1 S

IGNAL

EFINITIONS

Increasing Cx load on the electrode will result in a shorter

burst length. Since internal computations are based on burst

length, a shorter burst length means a smaller internal signal

number; conversely, a longer burst length means less Cx but

higher internal signal numbers. In summary:

Cx rises  shorter Burst Length  less internal signal

Cx drops  longer Burst Length  more internal signal

These relationships, are important to understand to avoid

confusion. They mirror signal values shown in QT3View and

the burst length as viewed on an oscilloscope.

2.8.2 S

ENSE

IRECTION

(SD)

OPTIONS: POS OR NEG; DEFAULT:

OSITIVE

The programmable SD option controls whether the device

responds to increases in Cx (‘normal’ detection) or decreases

in Cx (‘absence’ detection). The default mode is positive.

2.8.2.1 Positive Sense Direction (default)

This is the normal mode of operation for touch sensing.

Calibration is normally done when an object is not present;

OUT becomes active if an object approaches.

In this configuration, if Cx increases enough the internal

signal will pass the threshold level, and OUT will become

active. Cx must fall again so the internal signal traverses the

hysteresis level for OUT to become inactive.

The threshold and hysteresis levels are set relative to the

reference level determined during calibration.

2.8.2.2 Negative Sense Direction

In this mode, if the part is made to calibrate when an object is

present, OUT will become active if the object departs (Cx

decreases).

In this configuration, if Cx decreases enough the internal

signal will pass the threshold level, and OUT will become

active. Cx must rise again so the internal signal traverses the

hysteresis level for OUT to become inactive.

The threshold and hysteresis levels are set relative to the

reference level determined during calibration.

2.8.3 D

ETECT

ODE

(DM) S

ELECTION

OPTIONS: BG OR OBJ; DEFAULT:

The IC can be set to calibrate and detect in one of two

different modes to suit the application. The selection is made

using the cloning process.

The device default is BG. There are two BG modes, BG1 and

BG2, which must be further selected as described below. The

BG mode default is BG1.

OBJ mode is described in Section 2.8.5.

2.8.4 BG (B

ACKGROUND

) D

ETECTION

ODES

OPTIONS: BG1 OR BG2; DEFAULT:

The BG modes are useful when it is easier to calibrate on the

baseline signal level than the signal from the object to be

detected. The detection is always made relative to this

reference level, and the sensitivity is governed by the

adjustable threshold level (as well as capacitor Cs, and load

Cx). The BG modes are generally easier to use than OBJ.

There are two BG modes, BG1 and BG2. In these modes,

threshold and hysteresis values are calculated relative to the

reference level, which in turn is determined during calibration.

The two modes differ in that BG1 mode the calibration is

volatile whereas in BG2 mode the calibration reference is

stored in eeprom and reused until the next calibration.

Hysteresis can be altered as per Section 2.4.

9 QT310/R1.01 07/02

Sense direction (SD) behavior: In both BG modes OUT can

be made active on either positive or negative Cx changes

(Section 2.8.2). SD selection affects which side of the

reference the threshold and hysteresis points are placed.

In addition, the OUT pin can be made either active low or

active high (Section 2.7.1).

2.8.4.1 BG1 Mode (volatile reference)

In BG1 mode, the reference is set via recalibration initiated

using the /CAL_CLR pin or on power-up. The resulting

reference level is not stored into EEPROM. Max On-Duration

and drift compensation are able to function normally.

BG1 mode is useful when the signal can change slightly over

time and temperature, and it is useful to track these changes

without a loss of sensitivity.

2.8.4.2 BG2 Mode (stored reference)

In BG2 mode, the reference level is fixed and stored in

internal EEPROM. Drift compensation (Section 2.2) can be

used, but changes to the reference due to drift compensation

are not updated to EEPROM. Max On-Duration can also be

enabled (Section 2.6); if a MOD timeout occurs, the new

reference will be stored in EEPROM.

The reference is normally set during recalibration when the

/CAL_CLR pin pulses low (Section 1.6); the resulting

reference value is then stored in EEPROM. At power-up the

part automatically restores this reference level and runs

without another recalibration.

The reference value can also be entered numerically via the

cloning process (Table 4-1, page 14) to precisely replicate the

calibration point across many devices.

BG2 mode is useful when it is desired to lock in the reference

to prevent changes on startup, for example to replace

mechanical switches in process controls.

2.8.5 OBJ (O

BJECT

) D

ETECTION

ODE

This mode is useful to do a ‘learn by example’ calibration.

Typically, a test object is placed at the electrode in such a

way as to create a 50% signal level change relative to a

normal, full presentation of the object. The QT310 is then

calibrated in OBJ mode. Calibration in OBJ mode should

never be done with a full presentation of signal, as this will

create a marginal, unreliable detection.

This mode is suited to material detection, fluid level sensing,

and similar applications.

In OBJ mode, on calibration the current signal value is

recorded as a fixed threshold point and stored to EEPROM.

The hysteresis level is made relative to the fixed threshold,

and can be altered as with the BG modes. If hysteresis is too

large, the sensor can ‘stick’ on; hysteresis should normally be

set to a small value, just enough to prevent output chatter.

Hysteresis can also be made intentionally large, for example

for ‘bang-bang’ fluid level sensing, where an ‘upper’ level is

calibrated using OBJ, and a ‘lower’ cut-out level is defined by

the hysteresis value. The sensor must have SD = positive for

this mode (Section 2.8.2).

OBJ mode does not make use of a reference level and does

not allow drift compensation or Max On-Duration to operate.

The threshold point is fixed for all time until another

/CAL_CLR signal is received.

The OBJ threshold value can also be entered numerically via

the cloning process (Table 4-1, page 14) to precisely replicate

the threshold point across many devices.

Positive, negative detection mode behavior: In OBJ mode

OUT can be made active on either positive or negative signal

changes (Section 2.8.2). The signal direction selection affects

which side of the threshold the hysteresis level is placed after

calibration.

The OUT pin can be made either active low or active high

(Section 2.7.1).

2.9 SYNCHRONISATION

The synchronization feature allows a QT310 to generate its

burst on demand from an external trigger rather than of its

own accord. This feature is made possible by the fact that the

QT310 operates in burst mode, rather than continuously.

Sync is a powerful feature that permits two important

operating modes: Daisy-chaining, and noise synchronization.

The SYNC_I pin is used to trigger the QT310 to generate a

burst. The sleep timer will always wake the part if a sync

pulse has not been received before the sleep time expires.

The sleep timer is always restarted when a sync pulse is

received.

The pulse applied to SYNC_I must be normally high,

negative-going, of >15µs pulse duration. SYNC_O emits a

80µs pulse at the end of each burst.

During calibration (Section 1.6) and fast integration (Section

2.5), where bursts are generated quickly a number of times in

sequence without regard to the sleep timer, a single SYNC_O

pulse is generated only after the last burst in the series of fast

spaced bursts in order to prevent downstream slave parts

from being triggered too rapidly.

10 QT310/R1.01 07/02

Figure 2-3 Daisy chain wiring

OUT

Closed Loop

/SYNC_I

/SYNC_O

/CAL

6 /SYNC_I

/CAL

OUT2

OUT1

SENSOR N

SENSOR 1

Open Loop

/SYNC_O

/CAL

Vdd

/SYNC_I

2 /SYNC_O

Vdd

OUT_N

CS2

5CS1

SENSOR 2

Vdd

CS3

SNS1

SNS2

SNS1

SNS2

SNS1

SNS2

Vdd

2.9.1 D

AISY

-C

HAINING

QT310’

One use for synchronization is where two or more QT310’s in

close proximity to each other are synchronously daisy-

chained to avoid crosstalk (Figure 2-3).

One QT310 should be designated as the ‘Master’; this part

must have the shortest sleep time, while the downstream

parts which depend on the master and any intermediary

devices must have longer sleep time settings than the master.

The parts can be chained in a loop (switch set to ‘closed

loop’); in this configuration the master will generates a new

burst after the last slave has finished, making the scan

sequence of all devices the most time-efficient possible. If the

master doesn’t received a pulse before the sleep time has

elapsed it will generate a new burst. This mode is most useful

if there are a relatively small number of devices in the chain

and there is a need for fast response.

In open-loop, the rep rate of acquisition is set purely by the

burst rate of the master. It is possible in this mode to have

very long chains of parts with relatively good response time.

The disadvantage of this mode is that it is possible for the

bursts of downstream slaves to overlap with upstream

devices, potentially causing interference if their electrodes are

in physical proximity to each other.

It is also possible to devise a tree structure of devices, where

some devices in the chain trigger two or more slaves. This

speeds up the acquisition process considerably, but some

thought must be given to timing considerations so that

adjacent electrodes do not have bursts which overlap each

other in time.

After the burst has completed the QT310 checks the level on

SYNC_I. If SYNC_I is high, the part goes back to sleep; if

SYNC_I is still low the device waits until the SYNC_I is high

again before going back to sleep. If this is the case, power

drain will be higher so it is important to limit the pulse width to

an amount less than the burst length (but greater than

>15µs).

2.9.2 N

OISE

YNCHRONIZATION

Using the sync feature, a QT310 can be synchronized to a

repetitive external source of interference such as the power

line frequency (Figure 2-4) in order to dramatically reduce

signal noise. If line frequency is present near the sensors, this

feature should be used.

With this circuit the sensor can tolerate hundreds of volts per

meter of electric field. It is particularly useful for line-powered

touch controls.

Noise sync and daisy-chaining can be combined by having

the first device in the chain sync to the external noise source.

3 Circuit Guidelines

3.1 SAMPLE CAPACITORS

Cs capacitors can be virtually any plastic film or low to

medium-K ceramic capacitor. The normal usable Cs range is

from 1nF ~ 200nF depending on the sensitivity required;

larger values of Cs require higher stability to ensure reliable

sensing. Acceptable capacitor types include NP0 or C0G

ceramic, PPS film, Y5E and X7R ceramic in that order.

3.2 POWER SUPPLY

3.2.1 S

TABILITY

The QT310 derives its internal references from the power

supply. Sensitivity shifts and timing changes will occur with

changes in Vdd, as often happens when additional power

supply loads are switched on or off via the Out pin.

These supply shifts 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.

Detection ‘stiction’, the opposite effect, can occur if a load is

shed when the output is active and the signal swings are

small: the Out pin can remain stuck even if the detected

object is no longer near the electrode.

3.2.2 S

UPPLY

EQUIREMENTS

Vdd can range from 1.8 to 5.0 volts. If Setups programming is

required during operation, the minimum Vdd is 2.2V. Current

drain will vary depending on Vdd, the chosen sleep cycles,

and the burst lengths. Increasing Cx values will decrease

power drain since increasing Cx loads decrease burst length

(Figures 5-1 and 5-2).

If the power supply is shared with another electronic system,

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

spikes, sags, and surges. In BG1 mode the QT310 will track

slow changes in Vdd if drift compensation is enabled, but it

can be adversely affected by rapid voltage steps and spikes

at the millivolt level.

If desired, the supply can be regulated using a conventional

low current regulator, for example CMOS LDO regulators with

low quiescent currents, or standard 78Lxx-series 3-terminal

regulators.

For proper operation a 100nF (0.1uF) ceramic bypass

capacitor must be used between Vdd and Vss; the bypass

cap should be placed very close to the Vdd and Vss pins.

11 QT310/R1.01 07/02

Figure 2-4 Line sync circuit

SNS2

VSS

VDD

3SNS1

OUT

Vdd

/SYNC_O

SENSOR

OUT1

/SYNC_I

/CAL

4.7k - 10K

100pF

2.2nF

/SYNC_O

74HC14

U2:A

Line Input

470K-1M

3.3 PCB LAYOUT

3.3.1 G

ROUND

LANES

The use of ground planes around the device is encouraged

for noise reasons, but ground should not be coupled too close

to the sense pins in order to reduce Cx load. Likewise, the

traces leading from the sense pins to the electrode should not

be placed directly over a ground plane; rather, the ground

plane should be relieved by at least 3 times the width of the

sense traces directly under it, with periodic thin bridges over

the gap to provide ground continuity.

3.3.2 C

LONE

ORT

ONNECTO

If a cloning connector is used, place this close to the QT310.

Placing the cloning connector far from the QT310 will increase

the load capacitance Cx of the sensor line SNS1 and

decrease sensitivity. Long distances on these lines can also

make the cloning process more susceptible to communication

errors from ringing and interference.

If the SYNC_I input is used, a 1K ohm resistor should be used

to avoid conflicts with the cloning process (Figure 2-4, page

11).

Cloning can be designed for production by using pads (SMT

or through-hole) on the solder side which are connected to a

fixture via spring loaded ATE-style ‘pogo-pins’. This eliminates

the need for an actual connector to save cost.

Figure 3-1 ESD/EMC protection resistors

VSS

VDD

OUT

SNS2 /SYNC_I

SNS1

32 /SYNC_O

/CAL RE2

RE1

RE5

SENSOR

RE3

RE4

3.4 ESD ISSUES

In cases where the electrode is placed behind a dielectric

panel, the device will usually be well protected from static

discharge. However, even with a plastic or glass panel,

transients can still flow into the electrode via induction, or in

extreme cases, via dielectric breakdown. Porous materials

may allow a spark to tunnel right through the material; partially

conducting materials like 'pink poly' static dissipative plastics

will conduct the ESD right to the electrode. Panel seams can

permit discharges through edges or cracks.

Testing is required to reveal any problems. The QT310 has

internal diode protection which can absorb and protect the

device from most induced discharges, up to 20mA; the

usefulness of the internal clamping will depend on the

dielectric properties, panel thickness, and rise time of the

ESD transients.

ESD protection can be enhanced with an added resistor RE1

(Figure 3-1). As the transfer time is only 1us, the circuit can

tolerate values of RE1 which result in an RC time-constant of

about 200ns. The ‘C’ of the RC is the Cx load on the distant

side from the QT310. Thus, for a Cx load of 20pF, the

maximum RE1 should be 10K ohms. Larger amounts of RE1

will result in an increasingly noticeable loss of sensitivity.

3.5 EMC ISSUES

Electromagnetic and electrostatic susceptibility are often a

problem with capacitive sensors. QT310 behavior under these

conditions can be improved by adding RE1 (Figure 3-1),

exactly as for ESD protection. The resistor should be placed

next to the chip.

This works because the inbound RC network formed by RE1

and Cs has a very low cut-off frequency which can be

computed by the formula:

Fc =

2✜RCs

If R = 10K and Cs = 10nF, then Fc = 1.6kHz.

This leads to very strong suppression of external field effects.

Nevertheless, it is always wise to reduce lead lengths by

placing the QT310 as close to the electrode as possible.

Likewise, RF emissions are sharply curtailed by the use of

RE1, which bandwidth limits RF emissions based on the value

of RE1 and Cx, the electrode capacitance.

Line conducted EMI can be reduced by making sure the

power supply is properly bypassed to chassis ground. The

OUT line can also be paths for conducted EMI, and these can

be bypassed to circuit ground with an RC filter network. The

additional resistors RE2 through RE5 can also help with

conducted EMI.

4 Parameter Cloning

The cloning process allows user-defined settings to be loaded

into internal eeprom, or read back out, for development and

production purposes.

The QTM300CA cloning board in conjunction with QT3View

software simplifies the cloning process greatly. The E3B eval

board has been designed with a connector to facilitate direct

connection with the QTM300CA. The QTM300CA in turn

12 QT310/R1.01 07/02

Figure 4-1 Clone interface wiring

SCK

VSS

Vdd

VDD

SDI

SCK

/SYNC_I

/SYNC_O

SDO

/SYNC_O

SENSOR

/CAL

OUT

GND

SDO

SNS2

connects to any PC with a serial port which can run QT3View

software (included with the QTM300CA and available free on

Quantum’s web site).

The connections required for cloning are shown in Figure 4-1.

Further information on the cloning process can be found in

the QTM300CA instruction guide. Section 3.3.2 above

discusses wiring issues associated with cloning.

The parameters which can be altered are shown in Table 4-1,

page 14.

It is possible for a host controller to read and change the

internal settings via the interface connections shown, but

doing so will disturb the sensing process even when data

transfers are not occurring. The additional capacitive loading

of the interface pins will contribute to Cx; also, noise on the

interface lines can cause erratic operation.

The internal eeprom has a life expectancy of 100,000

erase/write cycles.

A serial interface specification for the device can be obtained

by contacting Quantum.

13 QT310/R1.01 07/02

countsReference (BG modes), Threshold (OBJ mode)65,536

-0 - 65536

REF

Reference / Thresh

Disabled1-Can only be disabled when SC = 00

Enabled0

HeartBeat

On1--0

Off0

TOGL

Toggle Latch

On1--0

Off0

TOGToggle

Active High1--0

Active Low0

OUTP

Output Polarity

Sleep1 - 255 -Burst rep interval = Tbs = SC x Ti

1 (~47ms Tbs

@3V)

No Sleep0

Sleep Cycles

Positive1 -

Negative: detects a drop of Cx

Positive: detects a rise of Cx

Negative0

SDSense Direction

BG21

BG1: The reference is volatile

BG2: Reference is stored in EEPROM

BG10

BG Mode

OBJ

1-0

BG0

Detection Mode

Tmod = (MOD + 1) x 16 x TbsSC > 0Infinite255 Seconds

Tmod = (MOD + 1) x 256 x TbsSC = 0

Finite0 - 254

MODMax-On Duration

Tpdc = (PDC + 1) x TbsSC > 0Off255 Seconds

Tpdc = (PDC + 1) x 16 x TbsSC = 0

100 (~4.36s/bit

@ 3V)

On0 - 254

PDC

Positive Drift Comp

Tndc = (NDC + 1) x TbsSC > 0Off255 Seconds

Tndc = (NDC + 1) x 16 x TbsSC = 0

2 (~0.13s/bit @

3V)

On0 - 254

NDC

Negative Drift Comp

Fast1

-1

Slow0

DISBEnd Det Integ. Speed

Fast1

-1

Slow0

DISA

Det Integrator Speed

Burst Cycles-10-1 - 256DIBT

End Det Integrator

Burst CyclesHigher = slower, more robust10-1 - 256DIATDet Integrator

CountsHigher = more hysteresis2-0 - 255HYSHysteresis

CountsHigher = less sensitive6-1 - 255THRThreshold

UnitCalculation / NotesDefaultValid ValuesSymbolDescription

TABLE 4-1: SETUPS SUMMARY CHART

14 QT310/R1.01 07/02

5 Electrical specifications

5.1 ABSOLUTE MAXIMUM SPECIFICATIONS

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

Storage temp........................................................................................ -65

C to +150

VDD...................................................................................................... -0.5 to +6V

Max continuous pin current, any control or drive pin.............................................................. ±40mA

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

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

Voltage forced onto any pin..................................................................... -1V to (Vdd + 0.5) Volts

5.2 RECOMMENDED OPERATING CONDITIONS

VDD....................................................................................................... +1.8 to 5V

VDD min required for eeprom programming of Setups.............................................................. +2.2V

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

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

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

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

5.3 AC SPECIFICATIONS

Vdd = 3.0, Ta = recommended operating range, Cs=100nF unless noted

µs80Output sync pulseT

SOP

µs15Input sync pulseT

SIP

µs15Heartbeat pulse widthT

Cs = 4.7nF to 200nF; Cx = 0ms250.5Burst lengthT

µs1Transfer durationT

µs3Charge durationT

Cs, Cx dependentms150Recalibration timeT

NotesUnitsMaxTypMinDescriptionParameter

5.4 SIGNAL PROCESSING

secsinfinite<1Post-detection recalibration timer duration

ms/level-Negative drift compensation rate

ms/level-Positive drift compensation rate

samples2561Consensus filter length

counts2540Hysteresis

counts2551Threshold differential

NotesUnitsMaxTypMinDescription

5.5 DC specifications

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

Ref Figs. 5-1, 5-2fF71,000Sensitivity rangeS

bits16Acquisition resolutionA

pF1000Load capacitance rangeC

OUT, 1.5mA sourceVVdd-0.6High output voltageV

OUT, 2mA sinkV0.4Low output voltageV

Vdd = 2.5 to 5.0VV0.6 VddInput high voltageV

Vdd = 2.5 to 5.0VV0.3 VddInput low voltageV

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

DDS

µA1,50060060Supply currentI

V51.8Supply voltageV

NotesUnitsMaxTypMinDescriptionParameter

15 QT310/R1.01 07/02

16 QT310/R1.01 07/02

Figure 5-1 Typical sensitivity vs Cx;

Threshold = 16, Vdd = 3.0 Volts

0.01

0.10

1.00

10.00

0 1020304050

Cx Load

Detection Threshold, pF

4.7nF

9nF

19nF

43nF

74nF

124nF

200nF

Figure 5-2 Typical sensitivity vs Cx;

Threshold = 6, Vdd = 3.0 Volts

0.01

0.10

1.00

10.00

0 1020304050

Cx Load

Detection Threshold, pF

4.7nF

9nF

19nF

43nF

74nF

124nF

200nF

Figure 5-3 Typical Burst length vs Cx, Cs;

Vdd = 3.0 Volts

52 118 228 507 884 1450 2357

Cx = 0pF

Cx = 21pF

Cx = 48pF

0.000

5.000

10.000

15.000

20.000

25.000

Burst Length (ms)

Sampling Capacitor (nF) Load (pf)

Figure 5-4 Typical Burst spacing vs Vdd;

SC = 1 and Tbd < 10ms

100

120

140

160

180

1.5 2 2.5 3 3.5 4 4.5 5 5.5

Power Supply (Volts)

Burst Spacing (ms)

17 QT310/R1.01 07/02

Figure 5-5 Typical internal signal count change vs Vdd

-2

1.5 2 2.5 3 3.5 4 4.5 5 5.5

Vdd (Volts)

Signal count variation (%)

Figure 5-6: Typical Signal Deviation vs. Temperature

Vdd = 5.0 Volts, Cx = 10pF, Cs = 5nF - 200nF PPS Film

18 QT310/R1.01 07/02

Figure 5-7 Power Consumption vs Cs

at Selected values of Sleep Cycles;

Cx = 10pF, Vdd = 2.0 Volts

100

150

200

250

300

350

400

450

0 102030405060

Sampling Capacitor (nF)

Cuurent (uA)

None

One

Two

Thre e

Five

Sleep Cycles

Figure 5-8 Power Consumption vs Cs

at Selected values of Sleep Cycles;

Cx = 10pF, Vdd = 3.3 Volts

100

200

300

400

500

600

700

800

900

0 102030405060

Sampling Capacitor (nF)

Current (uA)

None

One

Two

Three

Five

Ten

Sleep Cycles

Figure 5-9 Power Consumption vs Cs

at Selected values of Sleep Cycles;

Cx = 10pF, Vdd = 5.0 Volts

200

400

600

800

1000

1200

1400

1600

1800

2000

0 102030405060

Sampling Capacitor (nF)

Current (uA)

None

One

Two

Three

Five

Ten

Sleep Cycles

0.4310.9x

0.21-5.33-S1

0.150.1153.812.92S

-0.015-0.38r

BSC-0.1BSC-2.54F

0.0120.0080.3050.203L2

0.070.0451.781.14L1

0.0220.0140.5590.356L

0.0370.0270.940.69Q

Typical-0.3Typical-7.62m

0.40.35510.169.02M

0.3250.38.267.62A

0.280.247.116.1a

NotesMaxMinNotesMaxMin

InchesMillimeters

SYMBOL

Package type: 8-pin Dual-In-Line

0.0350.020.8890.508E

0.010.0070.2540.178e

0.080.072.031.78H

0.0130.0040.330.102h

0.020.0120.5080.305L

BSC0.05BSC1.27F

0.2120.2035.385.16M

0.330.38.387.62A

0.2130.2055.415.21a

NotesMaxMinNotesMaxMin

InchesMillimeters

SYMBOL

Package type: 8-pin Wide SOIC

19 QT310/R1.01 07/02

Pin 1

L1 L

Pin 1

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

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