CAP1133 datasheet(16/63 Pages) MICROCHIP

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CAP1133

DS00001625B-page 16

 2015 Microchip Technology Inc.

5.3.2.1

Manual Recalibration

The Calibration Activate Registers (Section 6.11, "Calibration Activate Register") force recalibration of selected sensor

inputs. When a bit is set, the corresponding capacitive touch sensor input will be recalibrated (both analog and digital).

The bit is automatically cleared once the recalibration routine has finished.

5.3.2.2

Automatic Recalibration

Each sensor input is regularly recalibrated at a programmable rate (see Section 6.17, "Recalibration Configuration Reg-

ister"). By default, the recalibration routine stores the average 64 previous measurements and periodically updates the

base “not touched” setting for the capacitive touch sensor input.

5.3.2.3

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

5.3.2.4

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").

5.3.3

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.

5.3.4

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").

5.3.5

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’.

Note:

During this recalibration routine, the sensor inputs will not detect a press for up to 200ms and the Sensor

Base Count Register values will be invalid. In addition, any press on the corresponding sensor pads will

invalidate the recalibration.

Note:

Automatic recalibration only works when the delta count is below the active sensor input threshold. It is dis-

abled when a touch is detected.

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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