8 Channel Capacitive Touch Sensor with 2 LED Drivers
Datasheet
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).
Table 5.8 DELTA_SENSE Bit Decode
DELTA_SENSE[2:0]
2
1
0
SENSITIVITY MULTIPLIER
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
128x (most sensitive)
64x
32x (default)
16x
8x
4x
2x
1x - (least sensitive)
Bits 3 - 0 - BASE_SHIFT[3:0] - Controls the scaling and data presentation of the Base Count registers.
The higher the value of these bits, the larger the range and the lower the resolution of the data
presented. The scale factor represents the multiplier to the bit-weighting presented in these register
descriptions.
APPLICATION NOTE: The BASE_SHIFT[3:0] bits normally do not need to be updated. These settings will not affect
touch detection or sensitivity. These bits are sometimes helpful in analyzing the Cap Sensing
board performance and stability.
SMSC CAP1128
Revision 1.32 (01-05-12)
DATA4S5HEET
SMSC [ SMSC CORPORATION ]
