MAS6510 datasheet(26/32 Pages) MAS

26 / 32 page

DA6510.009

6 September, 2018

26 (32)

TRIMMING FOR SENSOR CAPACITANCE (continued)

Example 2: Only CS_EXT varies but fixed CR_EXT exists

CS_EXT_MIN=9pF and CR_EXT_MAX=10pF at sensed parameter (pressure, humidity etc.) minimum

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



COFS = [0.9*14pF*(9pF-10pF)-0.1*9pF*(14pF-10pF)]/(0.9*14pF-0.1*9pF)= -1.38pF < 0



CR_INT = 0pF

a = 0.8

b = 0.9*(14pF+9pF-10pF)-0.1*(14pF+9pF-10pF)= 10.4pF

c = 0.9*14pF*(9pF-10pF)-0.1*9pF*(14pF-10pF)= -16.2 pF^2

CS_INT1 = {-10.4pF+

 [(10.4pF)^2-4*0.8*(-16.2)pF^2]}/2/0.8= 1.406pF

CS_INT2 = {-10.4pF-

 [(10.4pF)^2-4*0.8*(-16.2)pF^2]}/2/0.8= -14.406pF



CS_INT = 1.406pF

KRATIO = 0.1*(9pF+1.406pF)/(9pF+1.406pF-10pF-0pF) = 2.563

REGE3HEX = OCDACS = (1.406pF/22pF)*255 = 16.29  16DEC (CS capacitor matrix)

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

REGE5HEX = GRDAC = 193.8/2.563 = 75.61  76DEC (Gain register)

Example 3: 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 = [0.9*14pF*(10pF-14.5pF)-0.1*10pF*(14pF-10pF)]/(0.9*14pF-0.1*10pF) = -5.23pF < 0



CR_INT = 0pF

a = 0.8

b = 0.9*(14pF+10pF-14.5pF)-0.1*(14pF+10pF-10pF) = 7.15pF

c = 0.9*14pF*(10pF-14.5pF)-0.1*10pF*(14pF-10pF) = -60.7 pF^2

CS_INT1 = {-7.15pF+

 [(7.15pF)^2-4*0.8*(-60.7)pF^2]}/2/0.8 = 5.321pF

CS_INT2 = {-7.15pF-

 [(7.15pF)^2-4*0.8*(-60.7)pF^2]}/2/0.8 = -14.259pF



CS_INT = 5.321pF

KRATIO = 0.1*(10pF+5.321pF)/(10pF+5.321pF-14.5pF-0pF) = 1.866

REGE3HEX = OCDACS = (5.321pF/22pF)*255 = 61.68  62DEC (CS capacitor matrix)

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

REGE5HEX = GRDAC = 193.8/1.866 = 103.86  104DEC (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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