qt320 Quantum Research Group, qt320 Datasheet - Page 9

• Manufacturer Part Number: qt320
• Description: 2-channel Progammable Advanced Sensor Ic
• Manufacturer: Quantum Research Group

2.5 DETECT INTEGRATORS (DIA, DIB, DIS)
DIAT1, 2
DIBT1, 2
DIS
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 QT320 incorporates two detection
integrator (‘DI’) counters per channel that serve to confirm
detections and slow down response time. The counter pairs
operate independently for each sensing channel.
DIA / DIAT: The first counter, DIA, increments after each
burst if the signal threshold has been exceeded in that burst,
until DIA reaches its terminal count DIAT, after which the
corresponding OUT pin goes active. If the signal falls below
the threshold level prior to reaching DIAT, DIA resets.
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).
DIA1 / DIAT1 and DIA2 / DIAT2 are used in conjunction with
their respective channels.
DIB / DIBT: If OUT is active and the signal falls below the
hysteresis level, detect integrator DIB, counts up towards
terminal count DIBT; when DIBT is reached, OUT is
deactivated. DIBT is the same as DIAT if DIBT <= 6;
If DIAT > 6, then DIBT = 6.
DIBT cannot be adjusted separately from DIAT.
DIS: 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 is counting up. 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. The control bit for the fast DI
mode is referred to as DIS. DIS applies to both channels; it
cannot be enabled for just one channel.
DIS gear-shifts the effect of both 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 an OUT pin thus
preventing normal operation. To provide a way around this, a
Max On-Duration (‘MOD’) timer is provided to cause a
channel recalibration if the activation lasts longer than the
designated timeout, Tmod.
The timeout applies individually per channel. If one channel is
active for the Max On-duration interval it will recalibrate, but
the other channel will remain unaffected.
lQ
Range: 1..256
Range: 1..6
Range: 0, 1
Default: 10
Default: 6
Default: 1
9
The MOD function can also be disabled, in which case the
channel 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:
Example:
If SC = 0, Tmod is a function of the total combined burst
durations, Tbd. If SC = 0, the delay is:
Example:
If MOD = 255, recalibration timeout = infinite (disabled)
regardless of SC.
An MOD induced recalibration will make an 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
underlying channel will have recalibrated.
2.7 OUTPUT FEATURES
Available output processing options accommodate most
requirements; these can be set via the clone process.
Both OUT pins are open-drain, and require pullup resistors.
2.7.1 DC M
In DC mode the OUT pins respond to detections with a
steady-state active logic level, this state will endure for the
length of time that a detection exists or until a MOD timeout
occurs (Section 2.6).
The polarity of OUT can be set via the cloning process. Each
channel can be set for this feature independently. Either
active-low or active-high can be selected.
2.7.2 T
Toggle mode gives OUT pins a touch-on / touch-off flip-flop
action, so that its state changes with each detection. It is most
useful for controlling power loads, for example kitchen
appliances, power tools, light switches, etc.
MOD time-outs (Section 2.6) will recalibrate the underlying
channel but leave the OUT state unchanged.
OUT polarity (Section 2.7.1) has no effect when toggle mode
is engaged. The initial state at power-up of the OUT pins in
toggle mode is always open drain (logic high).
Each channel can be set individually for this feature.
OGGLE
Tmod = (MOD + 1) x 16 x Tbs
Tbs = 100ms,
MOD = 9;
Tmod = (9 + 1) x 16 x 100ms = 160 secs.
Tmod = (MOD + 1) x 256 x Tbd
Tbd = 18ms,
MOD = 9;
Tmod = (9 + 1) x 256 x 18ms = 46 secs.
ODE
M
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ODE
OLARITY
QT320/R1.03 08/02