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 QT1081 will
remain in full speed operation (20ms typical response time
and normal power consumption), as in Figure 2.2.
Figure 2.5 LP Pin High at End of Touch
touch
e
LP pin
bursts
low power
full speed
low power
Figure 2.2 Full Speed Operation
touch
LP pin
bursts
full speed operation
Note that the LP input must remain at one level (high or low)
for >150µs to guarantee that the QT1081 will recognise that
level.
Optimization of LP Mode:
For the lowest possible power
consumption when up to four keys are required, all keys
should be connected to QT1081 channels that are measured
during acquire burst B (i.e. k2, k3, k6 and k7). If this is done
the QT1081 automatically selects optimized LP operation,
which gives a significantly lower power consumption than
would be achieved if the burst A channels were used.
Optimized LP operation is identical to the standard LP
operation in all other ways; it is controlled as described above.
If the LP input is at a constant high level, then the QT1081 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
touch
e
LP pin
bursts
low power
full speed
low power
2.7 AKS™ Function Pins
The QT1081 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 also be
disabled, allowing any combination of keys to become active
at the same time. When operating, the modes are:
Global:
AKS functions operates across all eight keys. This
means that only one key can be active at any one time.
Groups:
AKS functions among two groups of four keys:
0-1-4-5 and 2-3-6-7. This means that up to two keys can be
active at any one time.
In Group mode, keys in one group have no AKS interaction
with keys in the other group.
Note that in Fast Detect mode, AKS can only be off.
While there is no touch, if the LP input is driven high then low,
the QT1081 will enter low power operation, as described
above, and remain in low power operation when LP is taken
low. When there is a touch the QT1081 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.
2.8 MOD_0, MOD_1 Inputs
In full option mode, 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
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.
Figure 2.4 LP Pin Low at End of Touch
touch
e
LP pin
bursts
low power
full speed
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 60 seconds.
2.9 Fast Detect Mode
lQ
9
QT1081_1R0.04_0307
QUANTUM [ QUANTUM RESEARCH GROUP ]
