MPR03X

Sensors

8

Freescale Semiconductor

Preliminary

3

Functional Overview

3.1

Introduction

The MPR03X has an analog front, a digital filter, and a touch recognition system. This data interpretation can be done many

different ways but the method used in the MPR03X is explained in this chapter.

3.2

Understanding the Basics

MPR03X is a touch pad controller which manages two or three touch pad electrodes. An I²C interface communicates with the

host, and an optional interrupt output advises the host of electrode status changes. The interrupt output is a multiplexed function

with the third electrode input, so using the interrupt output reduces the number of electrode inputs to two.

The primary application for MPR03X is the management of user interface touch pads. Monitoring touch pads involves detecting

small changes of pad capacitance. MPR03X incorporates a self calibration function which continually adjusts the baseline

capacitance for each individual electrode. Therefore, the host only has to configure the delta thresholds to interpret a touch or

release.

MPR03X uses a state machine to operate a capacitive measurement engine to analyze the electrodes and determine whether a

pad has been touched or released. Between measurements the MPR03X draws negligible current. The application controls

MPR03X's configuration, making trade-offs between noise rejection, touch response time, and power consumption.

3.3

Implementation

The touch sensor system can be tailored to specific applications by varying the following: a capacitance detector, a raw data low

pass filter, a baseline management system, and a touch detection system. In the following sections, the functionality and

configuration of each block will be described.

Electrodes can be connected to the MPR03X in two different configurations, one with an IRQ and one without (Figure 13).

Figure 13. MPR03X Pad and Interrupt Connection Options

1

2

3

ELE0

ELE1

ELE2

Interface

I²C Serial

VSS

SDA

SCL

MPR03X

ELE0

ELE1

VDD

INT

1

2

SDA

SCL

MPR03X

VDD

Interface

I²C Serial

VSS

VSS

75k

REXT

VSS

75k

REXT

MPR03X with 2 Electrodes and 2 Pads

MPR03X with 3 Electrodes and 3 Pads