CAP1106 datasheet(16/48 Pages) MICROCHIP

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CAP1106

DS00001624B-page 16

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5.2.2.3

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 acci-

dental 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 6.17, "Recalibration Configuration

5.2.2.4

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 6.6, "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 6.8,

"Sensor Input Configuration Register").

5.2.3

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.

5.2.4

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").

5.2.5

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’.

5.2.6

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.

5.3

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.

5.3.1

SENSOR INTERRUPT BEHAVIOR

The sensor interrupts are generated in one of two ways:

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.

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).

Note:

During this recalibration, the device will not respond to touches.

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.

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