CAP1203 datasheet(16/59 Pages) MICROCHIP

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4.4.1

AUTOMATIC RECALIBRATION

Each sensor input is regularly recalibrated at a programmable rate(see CAL_CFG[2:0] in Section 5.17, "Recalibration

Configuration Register"). By default, the recalibration routine stores the average 64 previous measurements and peri-

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

APPLICATION NOTE: Automatic recalibration only works when the delta count is below the active sensor input

threshold. It is disabled when a touch is detected.

4.4.2

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, recalibra-

tion when the pad is touched but delta counts do not exceed the threshold, or other environmental changes. When this

occurs, the base untouched sensor input may generate negative delta count values. The NEG_DELTA_CNT[1:0]

bits(see Section 5.17, "Recalibration Configuration Register") can be set to force a recalibration after a specified number

of consecutive negative delta readings. After a delayed recalibration (see Section 4.4.3, "Delayed Recalibration") the

negative delta count recalibration can correct after the touch is released.

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

4.4.3

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 5.6, "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[3:0] bits (see Section

5.8, "Sensor Input Configuration Register").

Note 4-1

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 settings.

Note 4-2

For the power button, which requires that the button be held longer than a regular button, the time

specified by the MAX_DUR[3:0] bits is added to the time required to trigger the qualifying event. This

will prevent the power button from being recalibrated during the time it is supposed to be held.

4.5

Power Button

The CAP1203 has a “power button” feature. In general, buttons are set for quick response to a touch, especially when

buttons are used for number keypads. However, there are cases where a quick response is not desired, such as when

accidentally brushing the power button causes a device to turn off or on unexpectedly.

The power button feature allows a sensor input to be designated as the “power button” (see Section 5.25, "Power Button

before an interrupt is generated; different times can be selected for the Standby and the Active states (see Section 5.26,

"Power Button Configuration Register"). The feature can also be enabled / disabled for both states separately.

APPLICATION NOTE: For the power button feature to work in the Standby and/or Active states, the sensor input

must be enabled in the applicable state.

After the designated power button has been held for the designated time, an interrupt is generated and the PWR bit is

set in the General Status Register (see Section 5.2, "Status Registers").

4.6

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 5.14, "Multiple Touch Pattern Configuration Register").

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