MPR081

Sensors

6

Freescale Semiconductor

DETAILED DESCRIPTION

FUNCTIONAL OVERVIEW

The MPR081user interface controller monitors various

combinations of capacitive touch pads, capacitive sliders,

capacitive rotaries, and mechanical keys. The device

includes a piezo buzzer driver which generates key click

sounds to provide audible feedback of pad touches and/or

key presses. The MPR081 also uses a standardized user

register set to configure the part on power up, and to read

pad, slider and key status. The commonality between

products in the MPR08 family of controllers simplifies

migration between parts.

A quick word on terminology:

–

A mechanical keyswitch is a switch containing, at its

simplest, two contacts which have either a high (>10 M

Ω)

or a low resistance (<10 k

Ω) between them depending on

switch position. Momentary push switches normally are

low resistance when pressed. Latching switches (such as

slide switches) provide high resistance in one position,

low resistance in the other.

–

A capacitive touch pad is a contactless 'key' which

detects the presence or absence of a finger. The raw

detection output is a single bit giving touch condition.

–

A capacitive rotary is a group of touch pads arranged in

a ring for which not only the presence or absence of a

finger is detected, but also the position of a finger along

the circumference of the rotary.

–

A capacitive slider is an elongated touch pad for which

not only the presence or absence of a finger is detected,

but also the position of a finger along the length of the

slider. The raw detection output is a single bit giving touch

condition, plus a multi-bit word for position. A typical

application is a volume control, where one end of the

slider corresponds to minimum volume and the other end

to maximum.

–A full pad is a touch pad whose conductive area is

connected to one electrode of the touch controller and

ground.

–A split pad is a touch pad whose conductive area is

connected to more than one electrode of the touch

controller. For the MPR08 family, a split pad is always

connected to two electrodes and typically looks like a pair

of interlaced fingers.

–A pad array is a collection of full and split pads

interconnected to each other and a number of electrode

lines. The number of pads available in a pad array with N

electrode lines using full and two-electrode split pads is

sum(1 to N), made up of N full pads and sum(1 to (N-1))

split pads. The MPR082 uses two sets of 4 electrode lines

and, therefore, each 4-electrode pad array has a

capability of 4 full pads and sum(1 to 3) or 1+2+3 = 6 split

pads, and a total pad count of sum(1 to 4) or 1+2+3+4 =

10 full plus split pads.

–

A pad array with n key lockout will only report one touch

at a time. Multiple simultaneous touches are ignored.

–

A pad array with 2 key rollover ignores further pads after

touching a first pad. If a pad is touched and held, and then

a second pad is touched, the second pad is ignored. If the

first pad is released while the second pad is still touched,

then the second pad will be reported as a new touch.

–

A pad array with n-key rollover allows any number of

pads will be detected as pressed in succession or

simultaneously without requiring any previous pads to be

released first.

Table 7. MPR08 Family Overview

Product

Bus

Sounder

Rotary Slider

Touch Pad Array

Main Attribute

MPR081

Yes

16-Positions

—

Highest resolution rotary

MPR082

Yes

—

1. The 20 pads are implemented by two independent arrays of 10 touch pads.

Two independent arrays of 10 touch pads