If the LP input is at a constant high level, then the QT1103
will enter low power operation whenever it is not detecting a
touch. It will switch automatically to full speed operation while
there is a touch, and revert to low power operation at the end
of the touch. This is shown in Figure 2.3.
Figure 2.3 Low Power/Full Speed Operation
e
touch
LP pin
bursts
full speed low power low power
While there is no touch, if the LP input is driven high then
low, the QT1103 will enter low power operation, as described
previously, and remain in low power operation when LP is
taken low. When there is a touch the QT1103 will switch
automatically to full speed operation. At the end of the touch
the choice of operation depends on the state of the LP input.
This is shown in Figures 2.4 and 2.5 - the first with the LP pin
being low at the end of the touch, and the second with the LP
pin being high at the end of the touch.
Figure 2.4 LP Pin Low at End of Touch
e
touch
LP pin
bursts
full speed
low powe
Figure 2.5 LP Pin High at End of Touch
e
touch
LP pin
bursts
full speed low power low power
Note that the LP input must remain at one level (high or low)
for >150µs to guarantee that the QT1103 will recognise that
level.
Optimization of LP Mode
For low power consumption, when up to eight keys are
required, all keys should be connected to QT1103 channels
that are measured during acquire bursts A and B
(i.e. K0...K7).
For the lowest possible power consumption, when up to four
keys are required, all keys should be connected to QT1103
channels that are measured during acquire burst B (i.e. K2,
K3, K6, K7).
If this is done the QT1103 automatically selects an optimized
LP operation, which gives a significantly lower power
consumption than would be achieved if additional acquire
bursts were used.
Optimized LP operation is identical to the standard LP
operation in all other ways; it is controlled as described
previously.
2.6 AKS™ Function Pins
The QT1103 features an adjacent key suppression (AKS™)
function with two modes. Option resistors act to set this
feature according to Tables 1.2 and 1.6. AKS can be
disabled, allowing any combination of keys to become active
at the same time. When operating, the modes are:
Global: The AKS function operates across all ten keys. This
means that only one key can be active at any one time.
Groups: The AKS function operates among three groups of
keys: 0-1-4-5, 2-3-6-7, and 8-9. This means that up to three
keys can be active at any one time.
In Group mode, keys in one group have no AKS interaction
with keys in any other group.
Note that in Fast Detect mode, AKS can only be off.
2.7 MOD_0, MOD_1 Inputs
In full option mode, the MOD_0 and MOD_1 resistors are
used to set the 'Max On-Duration' recalibration timeouts. If a
key becomes stuck on for a lengthy duration of time, this
feature will cause an automatic recalibration event of that
specific key only once the specified on-time has been
exceeded. Settings of 10s, 60s, and infinite are available.
The Max On-Duration feature operates on a key-by-key
basis; when one key is stuck on, its recalibration has no
effect on other keys.
The logic combination on the MOD option pins sets the
timeout delay; see Table 1.3.
Simplified mode MOD timing: In simplified mode, the max
on-duration is fixed at 60s.
2.8 Fast Detect Mode
In many applications, it is desirable to sense touch at high
speed. Examples include scrolling ‘slider’ strips or ‘Off’
buttons. It is possible to place the device into a ‘Fast Detect’
mode that usually requires under 14ms (typical) to respond.
This is accomplished internally by setting the Detect
Integrator to only three counts, i.e. only three successive
detections are required to detect touch.
In LP mode, ‘Fast’ detection will not speed up the initial delay
(which could be up to 190ms typical depending on the option
setting). However, once a key is detected the device is forced
back into normal speed mode. It will remain in this faster
mode until requested to return to LP mode.
When used in a ‘slider’ application, it is normally desirable to
run the keys without AKS.
In Fast mode the time required to process a key release is
reduced from three samples to two. Fast Detect mode can be
enabled as shown in Tables 1.2 and 1.6.
Lq
9 QT1103_3R0.03_0607
