MAS6512 datasheet(13/32 Pages) MAS

13 / 32 page

DA6512.003

2 December, 2016

13 (32)

CS AND CR CAPACITOR MATRIX REGISTERS (E3/63HEX AND E4/64HEX)

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

±10%.The CS capacitor matrix register (E3/63HEX)

has a corresponding EEPROM byte (C3/43HEX) for

storing the trim value. Also the CR capacitor matrix

byte (C4/44HEX) for storing the trim value. After

finding suitable CS and CR capacitor matrix register

values the trim values can be stored in the

corresponding non-volatile EEPROM addresses.

In normal operating mode these trim values are

automatically read from the EEPROM during each

conversion start. See also table 10 Trimming control

Table 4. CS capacitor matrix register (E3/63HEX), EEPROM (C3/43HEX)

Bit Number

Bit Name

Description

Value

Function

7-0

OCDACS

CDAC control bits

0HEX…FFHEX

CS offset trimming

Table 5. CR capacitor matrix register (E4/64HEX), EEPROM (C4/44HEX)

Bit Number

Bit Name

Description

Value

Function

7-0

OCDACR

CDAC control bits

0HEX…FFHEX

CR offset trimming

GAIN REGISTER (E5/65HEX)

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

-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 ΔΣ-modulator output:

CODEFS

CODE

AVE 



QAVE is the average measurement result (from the

over sampling) of the ΔΣ-modulator and varies from

0 to 1. The CODEFS is the maximum output code

which depends on OSR. See page 5 Full output

code

range

specification

the

Electrical

characteristics table. The linear signal range of the

modulator is from QAVE=10% to QAVE =90%.

In case of capacitance difference measurement

mode;

REF

AVE









In this mode the gain register value GRDAC sets

the VS level.

VS= (VDD/1.8V)*(33mV+GRDAC*2.88mV)

VR = (VDD/1.8V)*144mV

CS = External sensor + CS matrix capacitance

CR = External reference + CR capacitance

CREF = 6pF, three sigma variation ±10%

In case of capacitance ratio measurement mode;

AVE

















 1

In this mode the gain register value GRDAC sets

the VS level.

VS = (VDD/1.8V)*GRDAC*0.52mV

VR= (VDD/1.8V)*100.8mV

CS = External sensor + CS matrix capacitance

CR = External reference + CR capacitance

The gain register (E5/65HEX) has a corresponding

EEPROM byte (C5/45HEX). After finding a suitable

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. Gain register (E5/65HEX), EEPROM (C5/45HEX)

Bit Number

Bit Name

Description

Value

Function

7-0

GRDAC

RDAC control bits

0HEX…FFHEX

Gain control by sensor excitation signal

level control

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