8 Channel Capacitive Touch Sensor with 8 LED Drivers
Datasheet
3. Pulse 2 - The LED is configured to “Breathe” while actuated and then “Pulse” when the sensor is
released.
4. Breathe - The LED is configured to fade continuously ON-OFF-ON (i.e. to "Breathe”) with a
programmable rate and min / max brightness.
In addition to these four behaviors, all LED drivers support host initiated LED actuation. All LEDs also
have an option to assert the ALERT# pin when the initated behavior has reached its maximum or
minimum brightness levels.
4.4.1
Linking LEDs to Capacitive Touch Sensors
All LEDs can be linked to the corresponding Capacitive Touch Sense input channel so that when the
sensor detects a touch, the corresponding LED will be actuated at one of the programmed responses.
4.5
Capacitive Touch Sensing
The CAP1088 contains eight (8) independent Capacitive Touch Sensor inputs. Each sensor has
dynamic range to detect a change of capacitance due to a touch. Additionally, each sensor can be
configured to be automatically and routinely re-calibrated.
4.5.1
Sensing Cycle
Each Capacitive Touch Sensor has controls to be activated and included in the sensing cycle. When
the device is active, it automatically initiates a sensing cycle and repeats the cycle every time it
finishes. The cycle polls through each active Sensor starting with CS1 and extending through CS8. As
each Capacitive Touch Sensor is polled, its measurement is compared against a baseline “not touched”
measurement. If the delta measurement is large enough, then a touch is detected and an interrupt
generated.
The sensing cycle time is programmable (see Section 5.10).
4.5.2
Recalibrating Sensors
Each sensor is regularly recalibrated at an adjustable rate. By default, the recalibration routine stores
the average 256 previous measurements and periodically updates the base “Not Touched” setting for
the Capacitive Touch Sensor input.
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, then the base untouched sensor may generate negative delta count values. The device will
detect this condition based on a programmable number of consecutive negative delta readings. When
it detects the condition, the CAP1088 will automatically re-calibrate the base-count settings. During this
recalibration, the device will not respond to touches.
4.6
ALERT# Pin
The ALERT# pin is an active low output that is driven when an interrupt event is detected.
Whenever an interrupt is generated, the INT bit (see Section 5.1) is set. The ALERT# pin is cleared
when INT bit is cleared by the user. Additionally, when the INT bit is cleared by the user, status bits
are only cleared if no touch is detected.
4.6.1
Sensor Interrupt Behavior
The sensor interrupts are generated in one of two ways:
1. An interrupt is generated when a touch is detected and when a release is detected (see Figure 4.3).
Revision 1.1 (08-05-09)
SMSC CAP1088
DATA3S0HEET
SMSC [ SMSC CORPORATION ]
