at42qt2160 ATMEL Corporation, at42qt2160 Datasheet - Page 32

• Manufacturer Part Number: at42qt2160
• Description: Qslide?, 16-key Qmatrix? Sensor Ic
• Manufacturer: ATMEL Corporation

7.19
7.20
7.21
32
Address 22...37: Key Control
Address 38...53: Negative Threshold
Address 54...69: Burst Length
AT42QT2160
Table 7-20.
Table 7-21.
Table 7-22.
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
Default: 0 (AKS disabled)
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)
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.
Address
Address
Address
22...37
38...53
54...69
Key Control
Negative Threshold
Burst Length
Section 4.9.2 on page
b7
b7
b7
0
b6
b6
b6
0
10).
b5
b5
b5
0
BURST LENGTH
b4
b4
THRESHOLD
b4
0
b3
b3
b3
0
b2
b2
b2
0
b1
b1
b1
AKS GROUP
9502A–AT42–07/08
b0
b0
b0