8 Channel Capacitive Touch Sensor with 2 LED Drivers
Datasheet
4.5.2.1
Manual Recalibration
The Calibration Activate Registers (Section 5.11, "Calibration Activate Register") force recalibration of
selected sensor inputs. When a bit is set, the corresponding capacitive touch sensor input will be
recalibrated (both analog and digital). The bit is automatically cleared once the recalibration routine
has finished.
Note: During this recalibration routine, the sensor inputs will not detect a press for up to 200ms and
the Sensor Base Count Register values will be invalid. In addition, any press on the
corresponding sensor pads will invalidate the recalibration.
4.5.2.2
4.5.2.3
4.5.2.4
Automatic Recalibration
Each sensor input is regularly recalibrated at a programmable rate (see Section 5.17, "Recalibration
Configuration Register"). By default, the recalibration routine stores the average 64 previous
measurements and periodically updates the base “not touched” setting for the capacitive touch sensor
input.
Note: Automatic recalibration only works when the delta count is below the active sensor input
threshold. It is disabled when a touch is detected.
Negative Delta Count Recalibration
It is possible that the device loses sensitivity to a touch. This may happen as a result of a noisy
environment, an accidental recalibration during a touch, or other environmental changes. When this
occurs, the base untouched sensor input may generate negative delta count values. The
NEG_DELTA_CNT bits (see Section 5.17, "Recalibration Configuration Register") can be set to force
a recalibration after a specified number of consecutive negative delta readings.
Note: During this recalibration, the device will not respond to touches.
Delayed Recalibration
It is possible that a “stuck button” occurs when something is placed on a button which causes a touch
to be detected for a long period. By setting the MAX_DUR_EN bit (see Section 5.6, "Configuration
Registers"), a recalibration can be forced when a touch is held on a button for longer than the duration
specified in the MAX_DUR bits (see Section 5.8, "Sensor Input Configuration Register").
Note: Delayed recalibration only works when the delta count is above the active sensor input
threshold. If enabled, it is invoked when a sensor pad touch is held longer than the MAX_DUR
bit setting.
4.5.3
4.5.4
Proximity Detection
Each sensor input can be configured to detect changes in capacitance due to proximity of a touch.
This circuitry detects the change of capacitance that is generated as an object approaches, but does
not physically touch, the enabled sensor pad(s). When a sensor input is selected to perform proximity
detection, it will be sampled from 1x to 128x per sampling cycle. The larger the number of samples
that are taken, the greater the range of proximity detection is available at the cost of an increased
overall sampling time.
Multiple Touch Pattern Detection
The multiple touch pattern (MTP) detection circuitry can be used to detect lid closure or other similar
events. An event can be flagged based on either a minimum number of sensor inputs or on specific
sensor inputs simultaneously exceeding an MTP threshold or having their Noise Flag Status Register
bits set. An interrupt can also be generated. During an MTP event, all touches are blocked (see
Section 5.15, "Multiple Touch Pattern Configuration Register").
Revision 1.32 (01-05-12)
SMSC CAP1128
DATA3S4HEET
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