MAS6510 datasheet(24/32 Pages) MAS

24 / 32 page

DA6510.009

6 September, 2018

24 (32)

TRIMMING FOR SENSOR CAPACITANCE

MAS6510 in capacitance difference mode

Optimal trim settings which adjust capacitive signal to linear conversion range 10%...90% of the CDC are

calculated as follows. At first offset COFS_EXT of external capacitance ranges CS_EXT and CR_EXT is calculated.

COFS_EXT = (

CEXT_MIN + CEXT_MAX) / 2 =

= (CS_EXT_MIN

– CR_EXT_MAX + CS_EXT_MAX – CR_EXT_MIN) / 2

Equation 11.

The offset compensated to zero by using either CS_INT or CR_INT capacitor matrices depending on the offset

polarity.

If COFS_EXT

≥ 0pF

then CR_INT = COFS_EXT and CS_INT = 0pF

else CR_INT = 0pF and CS_INT = -COFS_EXT

Corresponding capacitance matrix register values (decimal) are calculated as follows.

REGE3HEX = OCDACS = (CS_INT/22pF)*255DEC

Equation 12.

REGE4HEX = OCDACR = (CR_INT/22pF)*255DEC

Equation 13.

Optimal gain coefficient (KDIFF) value scales capacitive signal to linear conversion range 10%...90% of the CDC

and it is calculated as follows.

KDIFF = 1.6*CREF / (

CEXT_MAX - CEXT_MIN) =

= 1.6*CREF / (CS_EXT_MAX

– CS_EXT_MIN + CR_EXT_MAX - CR_EXT_MIN)

Equation 14.

where CREF = 6pF ±10%.

Corresponding Gain register (REGE5HEX) value (decimal) can be solved from the equation 4 presented on page

22 as follows.

REGE5HEX = GRDAC = (KDIFF-0.229)/0.02

Equation 15.

Example 1: No external reference capacitor CR_EXT

CS_EXT_MIN = 8pF and CR_EXT_MAX = 0pF at sensed parameter (pressure, humidity etc.) minimum

CS_EXT_MAX = 12pF and CR_EXT_MIN = 0pF at sensed parameter (pressure, humidity etc.) maximum



CR_OFS_EXT = (8pF-0pF+12pF-0pF)/2=10pF

COFS_EXT

≥ 0



CR_INT = COFS_EXT = 10pF and CS_INT = 0

KDIFF = 1.6*6pF/(12pF-8pF+0pF-0pF) = 2.4



REGE3HEX = OCDACS = (0pF/22pF)*255 = 0DEC (CS capacitor matrix)

REGE4HEX = OCDACR = (10pF/22pF)*255 = 115.91  116DEC (CR capacitor matrix)

REGE5HEX = GRDAC = (2.4-0.229)/0.02 = 108.55  109DEC (Gain register)

Example 2: Both CS_EXT and CR_EXT vary but to opposite directions

CS_EXT_MIN = 10pF and CR_EXT_MAX = 14.5pF at sensed parameter (pressure, humidity etc.) minimum

CS_EXT_MAX = 14pF and CR_EXT_MIN = 10pF at sensed parameter (pressure, humidity etc.) maximum



COFS_EXT = (10pF-14.5pF+14pF-10pF)/2 = -0.25pF

COFS_EXT < 0



CR_INT = 0pF and CS_INT = -COFS_EXT = 0.25pF

KDIFF = 1.6*6pF/(14pF-10pF+14.5pF-10pF) = 1.129



REGE3HEX = OCDACS = (0.25pF/22pF)*255 = 2.90  3DEC (CS capacitor matrix)

REGE4HEX = OCDACR = (0pF/22pF)*255 = 0DEC (CR capacitor matrix)

REGE5HEX = GRDAC = (1.129-0.229)/0.02 = 45.00  45DEC (Gain register)

The found REGE3HEX, REGE4HEX and REGE5HEX trim register values need to be stored to corresponding non-

volatile EEPROM addresses. In I2C communication these are C3HEX, C4HEX and C5HEX but in SPI write

communication the addresses are 43HEX, 44HEX and 45HEX since in SPI write the MSB address bit is 0. See table

1 on page 9.

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