3 Channel Capacitive Touch Sensor with 3 LED Drivers
Datasheet
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.
4.3.3
4.3.4
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").
4.3.5
4.3.6
Low Frequency Noise Detection
Each sensor input has an EMI noise detector that will sense if low frequency noise is injected onto the
input with sufficient power to corrupt the readings. If this occurs, the device will reject the corrupted
sample and set the corresponding bit in the Noise Status register to a logic ‘1’.
RF Noise Detection
Each sensor input contains an integrated RF noise detector. This block will detect injected RF noise
on the CS pin. The detector threshold is dependent upon the noise frequency. If RF noise is detected
on a CS line, that sample is removed and not compared against the threshold.
4.4
ALERT# Pin
The ALERT# pin is an active low (or active high when configured) output that is driven when an
interrupt event is detected.
Whenever an interrupt is generated, the INT bit (see Section 5.1, "Main Control Register") is set. The
ALERT# pin is cleared when the 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.
4.4.1
Sensor Interrupt Behavior
The sensor interrupts are generated in one of two ways:
1. An interrupt is generated when a touch is detected and, as a user selectable option, when a release
is detected (by default - see Section 5.6). See Figure 4.3.
2. If the repeat rate is enabled then, so long as the touch is held, another interrupt will be generated
based on the programmed repeat rate (see Figure 4.2).
When the repeat rate is enabled, the device uses an additional control called MPRESS that determines
whether a touch is flagged as a simple “touch” or a “press and hold”. The MPRESS[3:0] bits set a
minimum press timer. When the button is touched, the timer begins. If the sensor pad is released
before the minimum press timer expires, it is flagged as a touch and an interrupt is generated upon
release. If the sensor input detects a touch for longer than this timer value, it is flagged as a “press
SMSC CAP1133
Revision 1.32 (01-05-12)
DATA2S1HEET
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