2 Device Operation
2.1 Reset and Startup Time
After a reset event, the device typically requires 260ms to
initialize, calibrate, and start operating normally. Keys will
work properly once all keys have been calibrated after reset.
The QT1103 does not have a brownout detector; its reset
input must be taken active (low) following power-up and when
Vdd falls below 2V.
2.5.2 Sync Mode
Sync mode allows the designer to synchronize acquire bursts
to an external signal source, such as mains frequency
(50/60Hz), to suppress interference. It can also be used to
synchronize two QT parts which operate near each other, so
that they will not cross-interfere if two or more of the keys (or
associated wiring) of the two parts are near each other.
The SYNC input is positive pulse triggered. Following each
rising edge the device will generate three acquire bursts in
C-A-B sequence.
2.2 Option Resistors
The option resistors are read on power-up only. There are
two primary option mode configurations: full, and simplified.
Full options mode:
Seven 1M option resistors are required
as shown in Figure 1.1. All seven resistors are mandatory.
Simplified mode:
A 1M resistor should be connected from
SNS6K to SNS7. In simplified mode, only one additional 1M
option resistor is required for the AKS feature (Figure 1.2).
Note that the presence and connection of option resistors will
influence the required values of Cs; this effect will be
especially noticeable if the Cs values are under 22nF. Cs
values should be adjusted for optimal sensitivity after the
option resistors are connected.
Figure 2.1 Acquire Bursts in C-A-B Sequence
SYNC
Burst C
Burst A
Burst B
If the SYNC input does not change level for ~150ms, the
QT1103 will free-run, generating a continuous stream of
acquire bursts C-A-B-C-A-B-C-A-... . While the QT1103 is in
free-run operation, a rising edge on the SYNC input will
return the QT1103 to synchronised operation.
Note that the SYNC input must remain at one level (high or
low) for >150µs to guarantee that the QT1103 will recognise
that level.
2.3 DETECT Pin
DETECT represents the functional logical-OR of all ten keys.
DETECT can be used to wake a battery-operated product
upon human touch.
The output polarity and drive of DETECT are governed
according to Table 1.4, page 6, and Table 1.7, page 7.
2.5.3 Low Power (LP) Mode
LP mode allows the device to be switched between full speed
operation (14ms (normal mode) or 28ms (fast mode) typical
response time and normal power consumption), and Low
Power operation (low average power consumption but an
increased maximum response time) according to the needs
of the application. There are three maximum response time
settings for low power operation: 70ms, 110ms, and 190ms
nominal; the response time setting is determined by option
resistors SL_1 and SL_0 (see Table 1.5). Slower response
times result in a lower average power drain.
Operation in low power mode is governed by the state of the
LP input and whether at least one key has a confirmed touch.
If the LP input is at a constant low level, then the QT1103 will
remain in full speed operation (14ms or 28ms typical
response time and normal power consumption), as in
Figure 2.2.
2.4 /CHANGE Pin
The /CHANGE pin can be used to tell the host that a change
in touch state has been detected (i.e. a key has been
touched or released), and that the host should read the new
key states over the serial interface. /CHANGE is pulled low
when a key state change has occurred.
/CHANGE is very useful to prevent transmissions with
duplicate data. If /CHANGE is not used, the host would need
to keep polling the QT1103 constantly, even if there are no
changes in touch. Upon detection of a key, /CHANGE will pull
low and stay low until the serial interface has been polled by
the host. /CHANGE will then be released and return high until
the next change of key state, either on or off, on any key
(Figures 2.6, 2.9).
The /CHANGE pin is open-drain, and requires a ~100k
pull-up resistor to Vdd in order to function properly.
Figure 2.2 Full Speed Operation
2.5 SYNC/LP Pin
2.5.1 Introduction
The SYNC / LP pin function is configured according to the
SL_0 and SL_1 resistor connections to either Vdd or Vss
(see Table 1.5).
touch
LP pin
bursts
full speed operation
Lq
8
QT1103_3R0.03_0607
QUANTUM [ QUANTUM RESEARCH GROUP ]
