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PDF QT310-IS Data sheet ( Hoja de datos )
| Número de pieza | QT310-IS | |
| Descripción | PROGRAMMABLE CAPACITANCE SENSOR IC | |
| Fabricantes | ETC | |
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LQ
QPROX™ QT310
PROGRAMMABLE CAPACITANCE SENSOR IC
Single channel digital advanced capacitance sensor IC
Spread spectrum burst modulation for high EMI rejection
Full autocal capability
User programmable via cloning process
Internal eeprom storage of user setups, cal data
Variable drift compensation & recalibration times
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
Fluid level sensors
Industrial panels
Appliance controls
Security systems
Access controls
Material detection
Micro-switch replacement Toys & games
This device requires only a few external passive parts to operate. It uses spread-spectrum burst modulation to dramatically
reduce interference problems.
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 permits electrodes from two or more QT310’s to be adjacent to each other without interference. The
burst rate can be programmed to a wide variety of settings, allowing the designer to trade off power consumption for response
time.
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 operating parameters can be
user-altered via Quantum’s cloning process to alter sensitivity, drift compensation rate, max on-duration, output polarity,
calibration mode, Heartbeat™ feature, and toggle mode. The settings are permanently stored in onboard eeprom.
The Quantum-pioneered HeartBeat™ signal is also included, allowing a host controller to monitor the health of the QT310
continuously if desired.
By using Quantum’s advanced, patented charge transfer principle, the QT310 delivers a level of performance clearly superior
to older technologies yet is highly cost-effective.
LQ
AVAILABLE OPTIONS
TA
00C to +700C
-400C to +850C
SOIC
-
QT310-IS
8-PIN DIP
QT310-D
-
Copyright © 2002 QRG Ltd
QT310/R1.03 21.09.03
1 page  
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 using a 750K resistor in series with probe)
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 DECREASING SENSITIVITY
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:
Tbd
Tbs
Tsc
Tmod
Tdet
Burst duration
Burst spacing
Sleep Cycle duration
Max On-Duration
Detection response time
(1.5.1)
(1.5.2)
(1.5.2)
(1.5.3)
(1.5.4)
The number of pulses in a burst and hence its duration
increases with Cs and decreases with Cx.
1.5.2 BURST SPACING: TBS, TSC
Between acquisition bursts, the device can go into a low
power sleep mode. The duration of this is a multiple of Tsc,
the basic sleep cycle time. Tsc depends heavily on Vdd as
shown in Figure 5-4, page 16. The parameter SC calls out
how many of these cycles are used. More SC means lower
power but also slower response time.
Tbs is the spacing from the start of one burst to the start of
the next. This timing depends on the burst length Tbd and the
dead time between bursts, i.e. Tsc.
The resulting timing of Tbs is:
Tbs = Tbd + (SC x Tsc)
-or-
Tbs = Tbd + 2.25ms
where SC > 0
where SC = 0
If SC = 0, the device never sleeps between bursts (example:
Figure 1-8). In this case the value of Tsc is fixed at about
2.25ms, but this time is not spent in Sleep mode and maximal
power is consumed.
if SC >> 0 (example: SC=15), the device will spend most of its
time in sleep mode and will consume very little power, but it
will be much 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.
1.5.1 BURST FREQUENCY AND DURATION
The burst duration depends on the values of Cs and Cx, and
to a lesser extend, Vdd. The burst is normally composed of
hundreds of charge-transfer cycles (Figure 1-6) operating at
about 240kHz. This frequency varies by about ±7% during the
burst in a spread-spectrum modulation pattern. See Section
3.5.2 page 13 for more information on spread-spectrum.
1.5.3 MAX ON-DURATION, TMOD
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 (see
Section 2.6).
Tmod restarts if the sensor becomes inactive before the end
of the Max On Duration period.
LQ
5 QT310/R1.03 21.09.03
5 Page 
During fast integration (Section 2.5), when 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.
If SC=0 (no sleep cycles), no Sync_O pulses are generated.
Disabling Sync: Connecting Sync_I to +Vdd will disable Sync
and the part will acquire bursts at the normal rate. If Sync is at
Vss, the device will wait for a Sync pulse, until the Tsc period
Vdd
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).
Line Input
R1
1M
R3
1M
2.2nF
C2
SENSOR
OUT1
U2:A
74HC14
C1
R4 100pF
4.7k - 10K
Vdd
U1
8
VDD
7 OUT
/CAL 1
3 SNS1
/SYNC_I 6
R2
470K-1M
2.9.2 NOISE SYNCHRONIZATION
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 up to 100V/M of AC
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.
CS 5 SNS2 /SYNC_O 2 /SYNC_O 3 Circuit Guidelines
VSS
4
Figure 2-4 Line sync circuit
expires; at that point the part will acquire regardless of the
absence of a Sync pulse.
2.9.1 DAISY-CHAINING QT310’S
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
should have the shortest SC sleep time, while the
downstream parts which depend on the master and any
intermediary devices should have longer sleep time settings
than the master.
The parts can be chained in a loop (Fig 2-4 switch set to
‘closed loop’); in this configuration the master will generate 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.
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 10nF ~ 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, Polypropylene film, and X7R ceramic in
that order.
3.2 POWER SUPPLY
3.2.1 STABILITY
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 SUPPLY REQUIREMENTS
Vdd can range from 2.0 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).
LQ
11 QT310/R1.03 21.09.03
11 Page | ||
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