qt511 Quantum Research Group, qt511 Datasheet - Page 3

• Manufacturer Part Number: qt511
• Description: Qwheel? Touch Slider Ic
• Manufacturer: Quantum Research Group

DETECT pin can be used to wake up the host when it goes
high upon touch.
In free-run mode, the device does not sleep between bursts.
In this mode the QT511 performs automatic drift
compensation at the maximum rate of one count per 1 20
acquisition burst cycles, or about one count every 7 seconds
without host intervention. It is not possible to change this
setting of drift compensation in Free-Run mode. See also
Section 3.3.3.
1.3 Sleep Mode
After an SPI transmission, the device will enter a low power
sleep state; see Figure 3-1, page 6, and Section 3.2.4, page
7 for details. This sleep state can be extended in order to
lower average power, by simply delaying the rise of /SS.
Coming out of sleep state when /SS is pulsed, the DETECT
and DRDY pins will float for ~400µs. It is recommended that
the DRDY pin be pulled to Vss with a resistor and DETECT
by bypassed with a capacitor to avoid false signalling if they
are being monitored during this time ; see Section 1.4.
Note: Pin /SS clamps to Vss for 250ns after coming out of
sleep state as a diagnostic pulse. To prevent a possible pin
drive conflict, /SS should either be driven by the host as an
open-drain pull-high drive (e.g. with a 100K pullup resistor), or
there should be a ~1K resistor placed in series with the /SS
pin. See Figure 1-1.
Note that activity on SCLK will also wake the QT511, which
in turn will then wait for the /SS to rise. For lowest possible
operation in Sleep mode, do not pulse on SCLK until after
/SS goes low.
1.4 DETECT Output Pin
This pin drives high when touch is detected and the chip is
reporting an angular position . This condition is also found as
bit 7 in the standard response.
This output will float for ~400µs during wake from Sleep mode
(see Section 1.3). It is recommended that the DETECT pin (if
it is used) be shunted to ground with a 1nF capacitor to hold
its state during the 400µs float interval when emerging from
Sleep.
lQ
Table 1-1 Pin Descriptions
Note (1): Pin floats ~400µs after wake from Sleep mode.
PIN
10
11
12
13
14
1
2
3
4
5
6
7
8
9
DETECT
NAME
SNS3B
SNS3A
SNS2B
SNS2A
SNS1B
SNS1A
DRDY
SCLK
VDD
SDO
VSS
/SS
SDI
Ground
TYPE
Power
I/O
I/O
I/O
I/O
I/O
I/O
O
O
O
I
I
I
DESCRIPTION
Positive power pin (+2.5 .. +5V)
Serial data output
Slave Select pin. This is an active low input that enables serial communications
Serial clock input. Clock idles high
Sense pin (to Cs3, Rs3); connects to 127/0 position (12:00) of wheel
Sense pin (to Cs3)
Sense pin (to Cs2, Rs2); connects to 85 position (8:00) of wheel
Sense pin (to Cs2)
Sense pin (to Cs1, Rs1); connects to 43 position (4:00) of wheel
Sense pin (to Cs1)
Serial data input
Active high touch detected. May be left unconnected. Note (1)
Data ready output. Goes high to indicate it is possible to communicate with the QT511. Note (1)
Negative power pin
3
Note that in the QT511, detection occurs when one or two of
the sensing channels becomes un balanced with respect to
the other channel(s). A touch at one position will always
cause such an imbalance. However, a signal change that is
balanced among all 3 channels will not cause a detection. For
example, if a book is placed on top of the rotor, the channels
will all change in the same way and as a result, detection will
be suppressed. This feature is significantly different from the
way the QT510 operates.
1.5 Position Data
The position value is internally calculated and can be
accessed only when the sensor is touched (Detect pin high).
The position data is a 7-bit number (0..127) that is computed
in real time; the position number returned is 0 or 127 with
position at SNS3, 43 when at SNS1 and 85 at SNS2. The
position data will update either with a single rapid touch or will
track if the finger is moved along the surface of the element.
The position data ceases to be reported when touch detection
is no longer sensed.
1.6 Calibration
Calibration is possible via two methods:
The calibration period requires 10 burst cycles, which are
executed automatically without the need for additional SPI
commands from the host. The spacing between each Cal
burst is 1ms, and the bursts average about 31ms each, i.e.
the Cal command requires ~325ms to execute. The power up
calibration has 6 extra bursts to allow for power supply
stabilization, and requires a total of ~550ms to begin normal
operation.
Calibration should be performed when there is no hand
proximity to the element, or the results may be in error.
Should this happen, the error flag (bit 1 of the standard
response, see Section 3.3) will activate when the hand is
withdrawn. In most cases this condition will self-correct if drift
compensation is used, and it can thus be ignored. See
Section 1.9 below.
1) Power up or power cycling (there is no reset input).
2) On command from the host via the SPI port
(Command 0x01: see Section 3.3.2).
QT511-ISSG R6.01/1005