Datasheet

32
9502A–AT42–07/08
AT42QT2160
7.19 Address 22...37: Key Control
AKS GROUP: these bits configure which AKS group a key is within (0 - AKS disabled, 1, 2 or 3).
Keys in the same group cannot both be in detect at the same time, unless they both form part of
the slider (see Section 4.9.2 on page 10).
Default: 0 (AKS disabled)
7.20 Address 38...53: Negative Threshold
The negative threshold value is established relative to a key’s signal reference value. The
threshold is used to determine key touch when crossed by a negative-going signal swing after
having been filtered by the detection integrator. Larger absolute values of threshold desensitize
keys since the signal must travel farther in order to cross the threshold level.
Conversely, lower thresholds make keys more sensitive.
As Cx and Cs drift, the reference point drift-compensates for these changes at a user-settable
rate; the threshold level is recomputed whenever the reference point moves, and thus it also is
drift compensated.
The amount of NTHR required depends on the amount of signal swing that occurs when a key is
touched. Thicker panels or smaller key geometries reduce “key gain", i.e. signal swing from
touch, thus requiring smaller NTHR values to detect touch.
Negative hysteresis: this is fixed at two less than the negative threshold value and cannot be
altered. It is implemented to stop keys from dithering in and out of detect.
NTHR Typical values:7 to 12
NTHR Default value: 10 (10 counts of threshold)
7.21 Address 54...69: Burst Length
The QT2160 uses a fixed number of pulses which are executed in burst mode. This number is
set in groups of four. Therefore, the value send to the QT2160 is multiplied by four to get the
actual number of burst pulses.
Table 7-20. Key Control
Addressb7b6b5b4b3b2b1b0
22...37000000AKS GROUP
Table 7-21. Negative Threshold
Addressb7b6b5b4b3b2b1b0
38...53 THRESHOLD
Table 7-22. Burst Length
Addressb7b6b5b4b3b2b1b0
54...69 BURST LENGTH