3 Channel Capacitive Touch Sensor with 3 LED Drivers
Datasheet
5.4
Sensor Input Delta Count Registers
Table 5.6 Sensor Input Delta Count Registers
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
Sensor Input 1
Delta Count
10h
11h
12h
R
Sign
64
32
16
8
4
2
1
00h
Sensor Input 2
Delta Count
R
R
Sign
Sign
64
64
32
32
16
16
8
8
4
4
2
2
1
1
00h
00h
Sensor Input 3
Delta Count
The Sensor Input Delta Count registers store the delta count that is compared against the threshold
used to determine if a touch has been detected. The count value represents a change in input due to
the capacitance associated with a touch on one of the sensor inputs and is referenced to a calibrated
base “Not Touched” count value. The delta is an instantaneous change and is updated once per sensor
input per sensing cycle (see Section 4.3.1, "Sensing Cycle").
The value presented is a standard 2’s complement number. In addition, the value is capped at a value
of 7Fh. A reading of 7Fh indicates that the sensitivity settings are too high and should be adjusted
accordingly (see Section 5.5).
The value is also capped at a negative value of 80h for negative delta counts which may result upon
a release.
5.5
Sensitivity Control Register
Table 5.7 Sensitivity Control Register
ADDR
R/W
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
1Fh
Sensitivity Control
-
DELTA_SENSE[2:0]
BASE_SHIFT[3:0]
2Fh
The Sensitivity Control register controls the sensitivity of a touch detection.
Bits 6-4 DELTA_SENSE[2:0] - Controls the sensitivity of a touch detection. The sensitivity settings act
to scale the relative delta count value higher or lower based on the system parameters. A setting of
000b is the most sensitive while a setting of 111b is the least sensitive. At the more sensitive settings,
touches are detected for a smaller delta capacitance corresponding to a “lighter” touch. These settings
are more sensitive to noise, however, and a noisy environment may flag more false touches with higher
sensitivity levels.
APPLICATION NOTE: A value of 128x is the most sensitive setting available. At the most sensitivity settings, the
MSB of the Delta Count register represents 64 out of ~25,000 which corresponds to a touch
of approximately 0.25% of the base capacitance (or a ΔC of 25fF from a 10pF base
capacitance). Conversely, a value of 1x is the least sensitive setting available. At these
settings, the MSB of the Delta Count register corresponds to a delta count of 8192 counts
out of ~25,000 which corresponds to a touch of approximately 33% of the base capacitance
(or a ΔC of 3.33pF from a 10pF base capacitance).
SMSC CAP1133
Revision 1.32 (01-05-12)
DATA2S9HEET
SMSC [ SMSC CORPORATION ]
