Datasheet

8 Channel Capacitive Touch Sensor with 8 LED Drivers
Datasheet
SMSC CAP1188 45 Revision 1.32 (01-05-12)
DATASHEET
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 4.5.1, "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
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 C 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 C of 3.33pF from a 10pF base capacitance).
16h R
Sensor Input 7
Delta Count
Sign 64 32 16 8 4 2 1 00h
17h R
Sensor Input 8
Delta Count
Sign 64 32 16 8 4 2 1 00h
Table 5.7 Sensitivity Control Register
ADDR R/W REGISTER B7 B6 B5 B4 B3 B2 B1 B0 DEFAULT
1Fh R/W Sensitivity Control - DELTA_SENSE[2:0] BASE_SHIFT[3:0] 2Fh
Table 5.8 DELTA_SENSE Bit Decode
DELTA_SENSE[2:0]
SENSITIVITY MULTIPLIER2 1 0
0 0 0 128x (most sensitive)
Table 5.6 Sensor Input Delta Count Registers (continued)
ADDR R/W REGISTER B7 B6 B5 B4 B3 B2 B1 B0 DEFAULT