QT411 Datasheet, PDF (2/12 Pages) Quantum Research Group – QSLIDE TOUCH SLIDER IC

1 Operation
Figure 1-1 QT411 Wiring Diagram
The QT411 uses a SPI slave mode
interface for control and data
VIN
Regulator
1
communications with a host
controller. Acquisition timings and
operating parameters are under host
control; there are no option jumpers
and the device cannot operate in a
stand-alone mode.
The output data is a 7-bit binary
number (0...127) indicating angular
position.
Like all QProx™ devices, the QT411
operates using bursts of
charge-transfer pulses; burst mode
permits an unusually high level of
VIN VOUT
C1
GND
C2
R1
2.2uF
2.2uF
22k
VDD
SNS3B ⁵
SPI BUS
1= Detect Output
R2
100k
R3
1k
C3
1nF
SNS3A ⁶
13 _DRDY
2 _SDO
3 _/SS
4 _SCLK
11 _SDI
SNS2A ⁸
SNS2B ⁷
SNS1A ¹⁰
12 _{DETECT SNS1B} 9
VSS
14
Rs3 4.7k
Cs3
100nF
Cs2
100nF
Rs2 4.7k
Cs1
100nF
Rs1 4.7k
Rs5 8.2k ^'RIGHT'
127
~400k
83
~400k
45
~400k
0
Rs4 8.2k _'LEFT'
control over spectral modulation,
power consumption, and response
time.
If power is not an issue the device can run constantly under
The QT411 modulates its bursts in a spread-spectrum
host control, by always raising /SS after 35µs from the last
fashion in order to heavily suppress the effects of external
rising edge of CLK. Constant burst operation can be used by
noise, and to suppress RF emissions.
the host to gather more data to filter the position data further
to suppress noise effects , if required.
1.1 Synchronized Mode
Refer also to Figure 3-1, page 6.
Sync mode allows the host device to control the rep etition
rate of the acquisition bursts, which in turn govern response
time and power consumption.
In sync mode, the device will wait for the SPI slave select line
/SS to fall and rise and will then do an acquisition burst;
actual SPI clocks and data are optional. The /SS pin thus
becomes a ‘sync’ input in addition to acting as the SPI
framing control.
Within 35µs of the last rising edge of CLK, the device will
enter a low power sleep mode. The rising edge of /SS must
occur after this time; when /SS rises, the device wakes from
sleep, and shortly thereafter does an acquisition burst. If a
more substantial sleep time is desired, /SS should be made
to rise some delay period later.
By increasing the amount of time spent in sleep mode, the
host can decrease the average current drain at the expense
of response time. Since a burst typically requires 31ms (at
3.3V, reference circuit), and an acceptable response time
might be ~100ms, the power duty cycle will be 31/100 or 31%
of peak current.
Synchronized mode also allows the host device to control the
rate of drift compensation, by periodically sending a ‘drift’
command to the device.
Mains Sync: Sync mode can and should be used to sync to
mains frequency via the host controller, if mains interference
is possible (ie, running as a lamp dimmer control). The host
should issue SPI commands synchronously with the mains
frequency. This form of operation will heavily suppress
interference from low frequency sources (e.g. 50/60Hz),
which are not easily suppressed using spread-spectrum pulse
modulation.
Cross-talk suppression: If two or more QT411’s are used in
close proximity, or there are other QTouch™ type device(s)
close by, the devices can interfere strongly with one another
to create position jitter or false triggering. This can be
suppressed by making sure that the devices do not perform
acquisition bursts at overlapping times. The host controller
can make sure that all such devices operate in distinctly
different timeslots, by using a separate /SS line for each part.
Acquire Burst
DRDY from QT
lQ
Figure 1-2 Free-Run Timing Diagram ( /SS = high )
~31ms
~31ms
<4ms
~30us
~25ms
2
QT411-ISSG R6.01/1005