8 Channel Capacitive Touch Sensor with 2 LED Drivers
Datasheet
4.4
LED Drivers
The CAP1128 contains two (2) LED drivers. Each LED driver can be linked to its respective capacitive
touch sensor input or it can be controlled by the host. Each LED driver can be configured to operate
in one of the following modes with either push-pull or open drain drive.
1. Direct - The LED is configured to be on or off when the corresponding input stimulus is on or off
(or inverted). The brightness of the LED can be programmed from full off to full on (default).
Additionally, the LED contains controls to individually configure ramping on, off, and turn-off delay.
2. Pulse 1 - The LED is configured to “Pulse” (transition ON-OFF-ON) a programmable number of
times with programmable rate and min / max brightness. This behavior may be actuated when a
press is detected or when a release is detected.
3. Pulse 2 - The LED is configured to “Pulse” while actuated and then “Pulse” a programmable
number of times with programmable rate and min / max brightness when the sensor pad is
released.
4. Breathe - The LED is configured to transition continuously ON-OFF-ON (i.e. to “Breathe”) with a
programmable rate and min / max brightness.
When an LED is not linked to a sensor and is actuated by the host, there’s an option to assert the
ALERT# pin when the initiated LED behavior has completed.
4.4.1
Linking LEDs to Capacitive Touch Sensor Inputs
All LEDs can be linked to the corresponding capacitive touch sensor input so that when the sensor
input detects a touch, the corresponding LED will be actuated at one of the programmed responses.
4.5
Capacitive Touch Sensing
The CAP1128 contains eight (8) independent capacitive touch sensor inputs. Each sensor input has
dynamic range to detect a change of capacitance due to a touch. Additionally, each sensor input can
be configured to be automatically and routinely re-calibrated.
4.5.1
Sensing Cycle
Each capacitive touch sensor input 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 input starting with CS1 and extending through
CS8. As each capacitive touch sensor input is polled, its measurement is compared against a baseline
“Not Touched” measurement. If the delta measurement is large enough, a touch is detected and an
interrupt is generated.
The sensing cycle time is programmable (see Section 5.10, "Averaging and Sampling Configuration
Register").
4.5.2
Recalibrating Sensor Inputs
There are various options for recalibrating the capacitive touch sensor inputs. Recalibration re-sets the
Base Count Registers (Section 5.24, "Sensor Input Base Count Registers") which contain the “not
touched” values used for touch detection comparisons.
APPLICATION NOTE: The device will recalibrate all sensor inputs that were disabled when it transitions from
Standby. Likewise, the device will recalibrate all sensor inputs when waking out of Deep
Sleep.
SMSC CAP1128
Revision 1.32 (01-05-12)
DATA3S3HEET
SMSC [ SMSC CORPORATION ]
