Table 1-1 Pin Descriptions
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
NAME
VDD
SDO
/SS
SCLK
SNS3B
SNS3A
SNS2B
SNS2A
SNS1B
SNS1A
SDI
PROX
DRDY
VSS
TYPE
Power
O
I
I
I/O
I/O
I/O
I/O
I/O
I/O
I
O
O
Ground
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 when hand approaches and during touch. May be left unconnected.
Note (1)
Data ready output. Goes high to indicate it is possible to communicate with the QT510.
Note (1)
Negative power pin
Note (1):
Pin floats ~400µs after wake from Sleep mode.
detector first, perhaps to wake a host controller. The PROX
pin can be used to wake up the host when it goes high.
In free-run mode, the device does not sleep between bursts.
In this mode the QT510 performs automatic drift
compensation at the maximum rate of one count per 180
acquisition burst cycles, or about one count every 3 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.
1.5 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.
1.3 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 rises, the PROX and
DRDY pins will float for ~400µs; it is recommended that these
pins be pulled low to Vss to avoid false signalling if they being
monitored during this time .
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.
N.B Activity on the clock line will wake the QT510, which in
turn will then wait for the SS to rise.
1.6 Calibration
Calibration is possible via two methods:
1) Power up or power cycling (there is no reset input).
2) On command from host via SPI (Command 0x01: see
Section 3.3.2).
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 1.5ms, and the bursts average about 31ms each, i.e.
the Cal command requires ~325ms to execute.
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 1.8 below.
Note: During calibration, the device cannot communicate.
DRDY will remain low during this interval.
1.4 PROX Output
There is an active-high output pin for the detection of hand
proximity.
PROX output:
This pin goes high when a hand is detected
in free space near the slider. This condition is also found
as bit 0 in the standard response when there is no touch
detection (Section 3.3).
The sensitivity of this function can be set using serial
commands (Sections 3.3.4 and 3.3.5).
This output will float for ~400µs after wake from Sleep mode
(see Section 1.3). It is recommended that PROX (if used) be
shunted to ground with 1nF capacitors to hold its state during
the 400µs float interval when emerging from Sleep.
1.7 Drift Compensation
The device features an ability to compensate for slow drift
due to environmental factors such as temperature changes or
humidity. Drift compensation is performed completely under
host control via a special drift command. See Section 3.3.3
for further details.
1.8 Error Flag
An error flag bit is provided in the standard response byte but
only when there is no touch detection present (Section 3.3); if
lQ
3
QT510 R6.04/0505
QUANTUM [ QUANTUM RESEARCH GROUP ]
