qt1080 Quantum Research Group, qt1080 Datasheet - Page 8

• Manufacturer Part Number: qt1080
• Description: 8 Key Qtouch? Sensor Ic
• Manufacturer: Quantum Research Group

2.7 AKS Function Pins
The QT1080 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
Groups: AKS functions among two groups of four keys:
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.
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 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 60 seconds.
2.9 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 1 0ms to respond. This is
accomplished internally by setting the Detect Integrator to
only two counts, i.e. only two successive detections are
required to detect touch.
In LP mode, ‘Fast’ detection will not speed up the initial
delay (which could be up to 360ms nominal 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 another LP pulse is received.
When used in a ‘slider’ application, it is normally desirable to
run the keys without AKS.
In both normal and ‘Fast’ modes, the time required to
process a key release is the same . It takes six sequential
confirmations of non-detection to turn a key off.
Fast Detect mode can be enabled as shown in Tables 1.2
and 1.6.
2.10 Simplified Mode
A simplified operating mode which does not require the
majority of option resistors is available. This mode is set by
connecting a resistor labelled SMR between pins SNS6K
and SNS7 (see Figure 1.2).
In this mode there is only one option possible - AKS enable
or disable. When AKS is disabled, Fast Detect mode is
enabled; when AKS is enabled, Fast Detect mode is off.
lQ
means that only one key can be active at any one time.
0-1-4-5 and 2-3-6-7. This means that up to two keys can
be active at any one time.
8
AKS in this mode is Global only (i.e. operates across all
functioning keys).
The other option features are fixed as follows:
See Tables 1.6 and 1.7.
2.11 Unused Keys
Unused keys should be disabled by removing the
corresponding Cs, Rs, and Rsns components and
connecting SNS pins as shown in the ‘Unused’ column of
Table 1.1. Unused keys are ignored and do not factor into
the AKS function (Section 2.7).
3 Design Notes
3.1 Oscillator Frequency
The QT1080’s internal oscillator runs from an external
resistor network connected to the OSC and SS pins as
shown in Figures 1.1 and 1.2 to achieve spread spectrum
operation. If spread spectrum mode is not required, the OSC
pin should be connected to Vdd with an 18K
Under different Vdd voltage conditions the resistor network
(or the solitary 18K
adjustment to obtain the specified burst center frequency.
The network should be adjusted slightly so that the positive
pulses on any key are approximately 2µs wide in the ‘solitary
18K
burst with the recommended spread -spectrum circuit (see
next section).
In practice, the pulse width has little effect on circuit
performance if it varies in the range from 1.5µs to 2.5µs. The
only effects will be seen in non-LP mode, as proportional
variations in Max On-Duration times and response times.
3.2 Spread-spectrum Circuit
The QT1080 offers the ability to spectrally spread its
frequency of operation to heavily reduce susceptibility to
external noise sources and to limit RF emissions. The SS pin
is used to modulate an external passive RC netw ork that
modulates the OSC pin. OSC is the main oscillator current
input. The circuit is shown in both Figures 1.1 and 1.2.
The resistors Rb1 and Rb2 should be changed depending
on Vdd. As shown in Figures 1.1 and 1.2, two sets of values
are recommended for these resistors depending on Vdd.
The power curves in Section 4.6 also show the effect of
these resistors.
The circuit can be eliminated , if it is not desired, by using an
18K
connecting SS to Vss with a 100K
consumes significantly less current than spread spectrum
mode.
The spread-spectrum RC network might need to be modified
slightly if the burst lengths are particularly long. Vdd
variations can shift the center frequency and spread slightly.
OUT_n, DETECT Pins: Push-pull, active high, direct
SYNC/LP Function: LP mode, ~200ms response time
Max On-Duration: 60 seconds
resistor’ mode, or 2.15µs wide at the beginning of a
resistor from OSC to Vdd to drive the oscillator, and
outputs
resistor) might require minor
QT1080 R11.06/0806
resistor. This mode
1% resistor.