QT110H-IS View Datasheet(PDF) - Quantum Research Group
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QT110H-IS Datasheet PDF : 12 Pages
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Figure 2-4
Getting HB pulses with a pull-down resistor (QT110 shown;
use pull-up resistor with QT110H)
Figure 2-5
Using a micro to obtain HB pulses in either output state
(QT110 or QT110H)
+2 .5 to 5
H eartBeat™ P ulses
1
2
Vdd
7
O UT
SNS2
Ro
3
O PT1
5
GAIN
P O RT_M.x
Ro
M icro processo r
2
OUT
3
OPT1
7
SN S 2
5
GA IN
4
O PT2
6
SNS1
Vss
8
P O RT_M.y
4
OPT2
6
SN S 1
Care should be taken when the IC and the load are both
powered from the same supply, and the supply is minimally
regulated. The device 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.
QT110: The output of the QT110 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-low. If desired the LED can be connected from
Out to ground, and driven on when the sensor is inactive, but
only with less drive current (1mA).
QT110H: This part is active-high, so it works in reverse to that
described above.
3.2 ELECTRODE WIRING
See also Section 3.4.
The wiring of the electrode and its connecting trace is important
to achieving high signal levels and low noise. Certain design
rules should be adhered to for best results:
1. Use a ground plane under the IC itself and Cs and Rs but
NOT under Re, or under or closely around the electrode or
its connecting trace. Keep ground away from these things
to reduce stray loading (which will dramatically reduce
sensitivity).
2. Keep Cs, Rs, and Re very close to the IC.
3. Make Re as large as possible. As a test, check to be sure
that an increase of Re by 50% does not appreciably
decrease sensitivity; if it does, reduce Re until the 50%
test increase has a negligible effect on sensitivity.
4. Do not route the sense wire near other ‘live’ traces
containing repetitive switching signals; the sense trace will
pick up noise from them.
3 - CIRCUIT GUIDELINES
3.1 SAMPLE CAPACITOR
When used for most applications, the charge sampler Cs can
be virtually any plastic film or good quality ceramic capacitor.
The type should be relatively stable in the anticipated
temperature range. If fast temperature swings are expected,
especially at higher sensitivity, a more stable capacitor might
be required for example PPS film.
In most moderate applications a low-cost X7R type will work
fine.
Figure 2-6 Eliminating HB Pulses
G AT E OR
MIC RO INP U T
CMO S
Co
100pF
2
O UT
3
O PT1
7
SN S 2
5
GA IN
4
O PT2
6
SN S 1
3.3 POWER SUPPLY, PCB LAYOUT
See also Section 3.4.
The power supply can range from 2.5 to 5.0 volts. At 2.5 volts
current drain averages less than 10µA with Cs = 10nF,
provided a 470K Rs resistor is used (Figure 2-6). Idd curves
are shown in Figure 4-4.
Higher values of Cs will raise current drain. Higher Cx values
can actually decrease power drain. Operation can be from
batteries, but be cautious about loads causing supply droop
(see Output Drive, Section 2.2.6) if the batteries are
unregulated.
As battery voltage sags with use or fluctuates slowly with
temperature, the IC 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
device. The IC will track slow changes in Vdd, but it can be
affected by rapid voltage steps.
if desired, the supply can be regulated using a conventional
low current regulator, for example CMOS LDO regulators that
have nanoamp quiescent currents. Care should be taken that
the regulator does not have a minimum load specification,
which almost certainly will be violated by the QT110's low
current requirement. Furthermore, some LDO regulators are
unable to provide adequate transient regulation between the
LQ
6
QT110/110H R1.03/0604
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