DA6510.009

6 September, 2018

22 (32)

CAPACITANCE MEASUREMENT MODES

MAS6510 has two capacitance measurement modes. Selection between modes is done by XRC bit in the

ratio mode by XRC=0. See table 3 on page 12.

Capacitance difference mode

In the capacitance difference mode the CDC output result (CODE) is proportional to capacitance difference

between CR and CC pins. See equation 3.



























−

+



=

























 

+



=

DIFF

REF

R

S

DIFF

REF

K

C

C

C

CODEFS

K

C

C

CODEFS

CODE

1

2

1

2

Equation 3.

where

CODEFS = Maximum output code range which depends on OSR selection. See page 7

“Full scale output code

range” specification in the ELECTRICAL CHARACTERISTICS table.

Equation 4.

Internal reference capacitor

External sensor + internal sensor matrix capacitance

Equation 5a.

between CS and CC pins

External reference + internal reference matrix capacitance

Equation 5b.

between CR and CC pins

Equation 5c.

Equation 5d.

Overall capacitance difference

Substituting equation 5d to equation 3 lead to equation 6.





























+



+



=

DIFF

REF

INT

EXT

K

C

C

C

CODEFS

CODE

1

2

Equation 6.

From equations 5c and 6 we see that offset trimming of the CODE is achieved using internal capacitance matrices

which define the

Internal capacitor matrix registers in tables 4 and 5). Gain trimming is achieved by gain register GRDAC value

The CDC output result (CODE) ranges from 0 to CODEFS. These correspond to following minimum (

and maximum (

(

INT

DIFF

REF

MIN

EXT

C

K

C

C



−

−

=



_

,

INT

DIFF

REF

MAX

EXT

C

K

C

C



−

=



_

Equations 7a, 7b

DIFF

REF

MIN

EXT

MAX

EXT

TOT

EXT

K

C

C

C

C



=



−



=



2

_

_

_

Equations 7c.

However linear measurement range of CDC is from 10% to 90% of CODEFS. To avoid non-linearity error in the

measurements the capacitive front-end should be trimmed to keep the measured external capacitance within the

linear measurement range of the CDC. In the linear measurement range the minimum (

maximum (

(