MAS6510 datasheet(25/32 Pages) MAS

25 / 32 page

DA6510.009

6 September, 2018

25 (32)

TRIMMING FOR SENSOR CAPACITANCE (continued)

MAS6510 in capacitance ratio mode

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

as follows.

COFS = [0.9*CS_EXT_MAX*(CS_EXT_MIN

– CR_EXT_MAX) – 0.1*CS_EXT_MIN *(CS_EXT_MAX - CR_EXT_MIN)] /

[0.9*CS_EXT_MAX - 0.1*CS_EXT_MIN]

Equation 16.

If COFS

≥ 0pF

then CR_INT = COFS and CS_INT = 0pF

else CR_INT = 0pF and CS_INT is calculated as follows.

a = 0.8

b = 0.9*(CS_EXT_MAX + CS_EXT_MIN

– CR_EXT_MAX) – 0.1*(CS_EXT_MAX + CS_EXT_MIN - CR_EXT_MIN) Equation 17a.

c = 0.9*CS_EXT_MAX *(CS_EXT_MIN

– CR_EXT_MAX) – 0.1*CS_EXT_MIN *(CS_EXT_MAX - CR_EXT_MIN)

Equation 17b.

CS_INT1 = [-b+

(b^2-4*a*c)]/2/a

Equation 17c.

CS_INT2 = [-b-

(b^2-4*a*c)]/2/a

Equation 17d.

If CS_INT1

≥ 0pF then CS_INT = CS_INT1 else CS_INT= CS_INT2

If CR_EXT does not exist (CR_EXT = 0pF) the equation 16 simplifies to following form.

COFS = CR_INT = 0.8*CS_EXT_MAX*CS_EXT_MIN / (0.9*CS_EXT_MAX - 0.1*CS_EXT_MIN)

Equation 18.

Corresponding capacitance matrix register (REGE3HEX and REGE4HEX) values (decimal) are calculated using

equations 12 and 13 presented on page 24.

Optimal gain coefficient (KRATIO) value is calculated as follows.

KRATIO = 0.1 * (CS_EXT_MIN + CS_INT) / (CS_EXT_MIN + CS_INT

– CR_EXT_MAX - CR_INT) =

Equation 19a.

= 0.9 * (CS_EXT_MAX + CS_INT) / (CS_EXT_MAX + CS_INT

– CR_EXT_MIN - CR_INT)

Equation 19b.

Corresponding Gain register (REGE5HEX) value (decimal) can be solved from the equation 10 presented on page

23 as follows.

GRDAC = 193.8/ KRATIO (see table 6 for Gain register setting)

Equation 20.

Example 1: Only CS_EXT varies and CR_EXT does not exist (CR_EXT = 0pF)

CS_EXT_MIN=4pF at sensed parameter (pressure, humidity etc.) minimum

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

CR_EXT_MIN/MAX = 0pF (no external reference capacitor)



COFS = 0.8*12pF*4pF/(0.9*12pF-0.1*4pF) = 3.69pF

≥ 0



CR_INT = COFS = 3.69pF and CS_INT = 0pF

KRATIO = 0.1*(4pF+0pF)/(4pF-0pF-0pF-3.69pF) = 1.3

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

REGE4HEX = OCDACR = (3.69pF/22pF)*255  43DEC (CR capacitor matrix)

REGE5HEX = GRDAC = 193.8/1.3 = 149.08  149DEC (Gain register)

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