CAP1298 datasheet(48/68 Pages) MICROCHIP

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CAP1298

DS00001571B-page 48

 2013-2015 Microchip Technology Inc.

APPLICATION NOTE: The programmed sensing cycle time (STDBY_CY_TIME[1:0] is only maintained if the actual

time to take the samples is less than the programmed cycle time. The STBY_AVG[2:0] bits

will take priority, so the sensing cycle time will be extended as necessary to accommodate

the number of samples to be measured.

5.23

Standby Sensitivity Register

The Standby Sensitivity register controls the sensitivity for sensor inputs enabled in Standby.

Bits 2 - 0 - STBY_SENSE[2:0] - Controls the sensitivity for sensor inputs that are enabled in Standby. The sensitivity

settings act to scale the relative delta count value higher or lower based on the system parameters. A setting of 000b is

the most sensitive while a setting of 111b is the least sensitive. At the more sensitive settings, touches are detected for

a smaller delta capacitance corresponding to a “lighter” touch. These settings are more sensitive to noise, however, and

a noisy environment may flag more false touches than higher sensitivity levels.

APPLICATION NOTE: A value of 128x is the most sensitive setting available. At the most sensitivity settings, the

MSB of the Delta Count register represents 64 out of ~25,000 which corresponds to a touch

of approximately 0.25% of the base capacitance (or a

C of 25fF from a 10pF base

capacitance). Conversely a value of 1x is the least sensitive setting available. At these

settings, the MSB of the Delta Count register corresponds to a delta count of 8192 counts

out of ~25,000 which corresponds to a touch of approximately 33% of the base capacitance

(or a

C of 3.33pF from a 10pF base capacitance).

TABLE 5-8:

STBY_CY_TIME BIT DECODE

STBY_CY_TIME[1:0]

Programmed Sensing Cycle Time

35ms

70ms (default)

105ms

140ms

TABLE 5-9:

STANDBY SENSITIVITY REGISTER

Addr

R/W

B5B4

B3B2

B1B0

Default

42h

R/W

Standby

Sensitivity

STBY_SENSE[2:0]

02h

TABLE 5-10:

STBY_SENSE BIT DECODE

STBY_SENSE[2:0]

Sensitivity Multiplier

210

128x (most sensitive)

001

64x

32x (default)

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