4. Functional Description

4.1 Capacitive Sensing Input

4.1.1 Introduction

The capacitive to digital converter uses an iterative, charge-timing self-capacitance technique to measure capacitance on an input pin.

Sampling is configured and controlled by settings in the non-volatile configuration profile, which can be changed through the 2-pin con-

figuration interface.

Baseline

Active threshold

Touch delta

Inactive threshold

Time

Figure 4.1. Capacitive Sense Data Types

4.1.2 Touch Qualification Criteria

The device detects a touch event when an inactive (untouched) input enabled by the input enable mask detects an sequence of meas-

urements that cross the active threshold.

The device detects a touch release event when an active (touched) input enabled by the input enable mask detects an sequence of

measurements that cross the inactive threshold.

The debounce configuration profile parameter defines how many measurements in a row must cross a threshold before a touch or re-

lease is qualified. In electrically noisy environments more heavily filtered data is used for qualification.

4.1.3 Thresholds

Capacitive sensing inputs use input-specific thresholds for touch qualification. Each input uses two thresholds, one to detect inactive-to-

active transitions on the input, and another to determine active-to-inactive transitions on the input. The inputs use two thresholds to add

hysteresis and prevent active/inactive ringing on inputs. Each threshold can be set through Simplicity Studio tools and all thresholds are

stored in non-volatile memory in the device's configuration profile.

Thresholds are defined as percentages of a capacitive sensing input's touch delta.

CPT112S Data Sheet

Functional Description

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