CAP1293 datasheet(18/63 Pages) MICROCHIP

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CAP1293

DS00001566B-page 18

 2013-2015 Microchip Technology Inc.

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 CAP1293 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").

4.8

Noise Controls

4.8.1

LOW FREQUENCY NOISE DETECTION

Each sensor input has a low frequency noise detector that will sense if low frequency noise is injected onto the input

with sufficient power to corrupt the readings. By default, if this occurs, the device will reject the corrupted samplesee

DIS_ANA_NOISE bit in Section 5.6.1, "Configuration - 20h") and the corresponding bit is set to a logic ‘1’ in the Noise

Flag Status register (see SHOW_RF_NOISE bit in Section 5.6.2, "Configuration 2 - 44h").

4.8.2

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. By default, if RF noise is detected on a CS line, that sample

is removed and not compared against the threshold (see DIS_RF_NOISE bit in Section 5.6.2, "Configuration 2 - 44h").

FIGURE 4-3:

SIGNAL GUARD

CAP129X Device

CS pin

SIGNAL_GUARD

CS pin

Touch Pad

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