CAP1298 datasheet(16/68 Pages) MICROCHIP

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CAP1298

DS00001571B-page 16

 2013-2015 Microchip Technology Inc.

4.1

Power States

The CAP1298 has 4 power states depending on the status of the STBY, COMBO, and DSLEEP bits. When the device

transitions between power states, previously detected touches (for channels that are being de-activated) are cleared

and the sensor input status bits are reset.

Active - The normal mode of operation. The device is monitoring capacitive sensor inputs enabled in the Active

state.

Standby - When the STBY bit is set, the device is monitoring the capacitive sensor inputs enabled in the Standby

state. Interrupts can still be generated based on the enabled channels. The device will still respond to communi-

cations normally and can be returned to the Active state of operation by clearing the STBY bit. Power consump-

tion in this state is dependent on the number of sensor inputs enabled as well as averaging, sampling time, and

cycle time.

Combo - When the COMBO bit is set, the device is monitoring capacitive sensor inputs enabled in the Active

state as well as inputs enabled in the Standby state (hence the name “Combo”). Interrupts can still be generated

based on the enabled channels. The device will still respond to communications normally and can be returned

to the Active state of operation by clearing the COMBO bit. Power consumption in this state is dependent on the

number of sensor inputs enabled as well as averaging, sampling time, and cycle time.

Deep Sleep - When the DSLEEP bit is set, the device is in its lowest power state. It is not monitoring any capac-

itive sensor inputs. While in Deep Sleep, the CAP1298 can be awakened by SMBus communications targeting

the device. This will not cause the DSLEEP to be cleared so the device will return to Deep Sleep once all com-

munications have stopped. The device can be returned to the Active state of operation by clearing the DSLEEP

bit.

4.2

Reset

The Power-On Reset (POR) circuit holds the device in reset until VDD has reached an acceptable level, Power-on Reset

Release Voltage (VPORR), for minimum operation. The power-up timer (PWRT) is used to extend the start-up period until

all device operation conditions have been met. The power-up timer starts after VDD reaches VPORR. POR and PORR

with slow rising VDD is shown in Figure 4-2.

The Brown-Out Reset (BOR) circuit holds the device in reset when VDD falls to a minimum level, VBOR for longer than

the BOR reset delay (tBORDC). After a BOR, when VDD rises above VPORR, the power-up timer is started again and must

finish before reset is released, as shown in Figure 4-2.

4.3

Capacitive Touch Sensing

The CAP1298 contains eight (8) 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 recalibrated.

4.3.1

CAPACITIVE TOUCH SENSING SETTINGS

Controls for managing capacitive touch sensor inputs are determined by the power state.

FIGURE 4-2:

POR AND PORR WITH SLOW RISING VDD AND BOR WITH FALLING VDD

VDD

VBOR

TPWRT

GND

Undefined

SYSRST

VPOR

VPORR

TBORDC TPWRT

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