CAP1133 datasheet(24/63 Pages) MICROCHIP

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CAP1133

DS00001625B-page 24

 2015 Microchip Technology Inc.

The value presented is a standard 2’s complement number. In addition, the value is capped at a value of 7Fh. A reading

of 7Fh indicates that the sensitivity settings are too high and should be adjusted accordingly (see Section 6.5).

The value is also capped at a negative value of 80h for negative delta counts which may result upon a release.

6.5

Sensitivity Control Register

The Sensitivity Control register controls the sensitivity of a touch detection.

Bits 6-4 DELTA_SENSE[2:0] - Controls the sensitivity of a touch detection. The sensitivity settings act to scale the rel-

ative 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 with 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

ΔC 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

ΔC of 3.33pF from a 10pF base capacitance).

Bits 3 - 0 - BASE_SHIFT[3:0] - Controls the scaling and data presentation of the Base Count registers. The higher the

value of these bits, the larger the range and the lower the resolution of the data presented. The scale factor represents

the multiplier to the bit-weighting presented in these register descriptions.

APPLICATION NOTE: The BASE_SHIFT[3:0] bits normally do not need to be updated. These settings will not affect

touch detection or sensitivity. These bits are sometimes helpful in analyzing the Cap Sensing

board performance and stability.

TABLE 6-7:

SENSITIVITY CONTROL REGISTER

ADDR

R/W

Default

1Fh

R/W

Sensitivity Control

DELTA_SENSE[2:0]

BASE_SHIFT[3:0]

2Fh

TABLE 6-8:

DELTA_SENSE BIT DECODE

DELTA_SENSE[2:0]

Sensitivity Multiplier

210

128x (most sensitive)

001

64x

32x (default)

011

16x

100

101

110

1x - (least sensitive)

TABLE 6-9:

BASE_SHIFT BIT DECODE

BASE_SHIFT[3:0]

Data Scaling Factor

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