CAP1026 datasheet(37/70 Pages) SMSC

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6 Channel Capacitive Touch Sensor with 2 LED Drivers

Datasheet

SMSC CAP1026

Revision 1.1 (08-05-09)

DATASHEET

The Sensor Delta Count registers store the delta count that is compared against the threshold used to

determine if a touch has been detected. The count value represents a change in input due to the

capacitor associated with a touch on one of the sensors and is referenced to a calibrated base “Not

touched” count value. The delta is an instantaneous change and is updated once per sensor per

sensing cycle (see Section 4.5.1 - sensor cycle).

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 5.5).

The value is also capped at a negative value of FFh for negative delta counts which may result upon

a release.

5.5

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 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 C 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

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).

11h

Sensor 2 Delta

Count

Sign

00h

12h

Sensor 3 Delta

Count

Sign

00h

13h

Sensor 4 Delta

Count

Sign

00h

14h

Sensor 5 Delta

Count

Sign

00h

15h

Sensor 6 Delta

Count

Sign

00h

Table 5.6 Sensitivity Control Register

ADDR

R/W

DEFAULT

1Fh

R/W

Sensitivity Control

DELTA_SENSE[2:0]

BASE_SHIFT[3:0]

2Fh

Table 5.5 Sensor Delta Count Registers (continued)

ADDR

R/W

DEFAULT

CAP1026 Datasheet(PDF) 37 Page - SMSC Corporation

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