CAP1126 Datasheet, PDF (26/73 Pages) Microchip Technology – 6 Channel Capacitive Touch Sensor with 2 LED Drivers

CAP1126
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.
5.5.3 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.
5.5.4 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 exceed-
ing 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 6.15, "Multiple Touch Pattern Configuration Register").
5.5.5 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 suffi-
cient 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’.
5.5.6 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.
5.6 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 6.1, "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.
5.6.1 SENSOR INTERRUPT BEHAVIOR
The sensor interrupts are generated in one of two ways:
1. An interrupt is generated when a touch is detected and, as a user selectable option, when a release is detected
(by default - see Section 6.6). See Figure 5-3.
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 5-2).
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 and hold” event. So long as the touch is held, interrupts will be generated at the programmed
repeat rate and upon release (if enabled).
APPLICATION NOTE: Figure 5-2 and Figure 5-3 show default operation which is to generate an interrupt upon
sensor pad release and an active-low ALERT# pin.
APPLICATION NOTE: The host may need to poll the device twice to determine that a release has been detected.
DS00001623B-page 26
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