DA6512.000

11 July, 2012

11 (26)

There are two internal capacitor matrices that add

capacitance in parallel to the sensor capacitor (CS)

and the reference capacitor (CR). These offset

capacitances are used to adjust the sensor signal to

an optimal range. Each capacitor matrix has a

selectable capacitance from 0pF up to 22pF in

typical 86fF steps. The three sigma process

variation of the capacitor matrix capacitance is

storing the trim value. Also the CR capacitor matrix

finding suitable CS and CR capacitor matrix register

values the trim values can be stored in the non-

volatile EEPROM.

In normal operating mode these trim values are

automatically read from the EEPROM during each

conversion start. See also table 9 Trimming control

Table 4.

Bit Number

Bit Name

Description

Value

Function

7-0

OCDACS

CDAC control bits

CS offset trimming

Table5.

Bit Number

Bit Name

Description

Value

Function

7-0

OCDACR

CDAC control bits

CR offset trimming

The gain register sets the excitation signal level for

the capacitive sensor. The eight bits (GRDAC) can

be programmed to values between 0 and 255.

Together with the CS and the CR capacitor matrix

trim parameters it’s used to adjust the sensor signal

to an optimal range. The goal is to get a maximum

dynamic range and keep the signal within linear

input range of the ∆Σ-modulator. This condition is

met when the signal minimum and maximum

covers the whole linear input range.

The

output

of

MAS6512

has

the

following

relationship to the Σ-modulator output:

RANGE

AVE

OUT

CODE

Q

CODE

⋅

=

over sampling) of the

Σ-modulator and varies from

which depends on OSR and measurement mode

selections. See page 5 Full output code range

specification in the Electrical characteristics table.

The linear signal range of the modulator is from

In case of capacitance difference measurement

mode;

R

S

REF

R

S

AVE

V

V

C

C

C

Q

∗

∗

−

+

=

2

2

1

In this mode the gain register value GRDAC sets

In case of capacitance ratio measurement mode;

S

R

S

R

AVE

V

V

C

C

Q

∗













−

= 1

In this mode the gain register value GRDAC sets

gain register value it can be stored in the EEPROM

memory. In normal operating mode the gain trim

value is read automatically from the EEPROM

during each conversion start.

Table 6.

Bit Number

Bit Name

Description

Value

Function

7-0

GRDAC

RDAC control bits

Gain control by sensor excitation signal

level control