CAP1296 datasheet(19/68 Pages) MICROCHIP

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DS00001569B-page 19

CAP1296

4.5

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). Generally, sensor inputs used to detect proximity have physically larger pads than standard buttons. In addition,

gain should be increased to increase sensitivity. To improve the signal, the signal guard feature may be used.

4.5.1

SIGNAL GUARD

The signal guard isolates the signal from virtual grounds, as shown in Figure 4-3. It can be used to isolate the proximity

antenna from nearby conductive surfaces that would otherwise attenuate the e-field.

4.6

Power Button

The CAP1296 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 5.26, "Power Button

before an interrupt is generated; different times can be selected for the Standby and the Active states (see Section 5.27,

"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. If the power button feature is enabled for both

Standby and Active and the COMBO bit is set, the Standby power button settings will be

used.

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").

4.7

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 5.15, "Multiple Touch Pattern Configuration Register").

FIGURE 4-3:

SIGNAL GUARD

CAP129X Device

CS pin

SIGNAL_GUARD

CS pin

Touch Pad

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