CAP1126 datasheet(25/73 Pages) MICROCHIP

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DS00001623B-page 25

CAP1126

5.5

Capacitive Touch Sensing

The CAP1126 contains six (6) 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.

5.5.1

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 CS6. 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 6.10, "Averaging and Sampling Configuration Register").

5.5.2

RECALIBRATING SENSOR INPUTS

There are various options for recalibrating the capacitive touch sensor inputs. Recalibration re-sets the Base Count Reg-

isters (Section 6.24, "Sensor Input Base Count Registers") which contain the “not touched” values used for touch detec-

tion 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.

5.5.2.1

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.

5.5.2.2

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.

5.5.2.3

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

5.5.2.4

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").

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.

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