MAS6512 datasheet(23/32 Pages) MAS

23 / 32 page

DA6512.003

2 December, 2016

23 (32)

TRIMMING FOR SENSOR CAPACITANCE

MAS6512 in capacitance ratio mode

The reference capacitor CR is calculated from

CR = [CS MIN*CS MAX*(DMAX-DMIN)] / (CS MAX*DMAX-CS MIN*DMIN)

If an external CR is used, it is connected between pins CR and CC. If an internal CR is used, the trim code for CR

is calculated from

REGE4HEX = (CR/CR MAX)*255

where CR MAX is nominally 22pF, but subject to ±10 % (±3 sigma) process variation.

The reference voltage, VS, can be calculated using the following equation:

VS = 100.8mV * (CS MAX-CS MIN) / (CS MAX*DMAX-CS MIN*DMIN)

The gain register trim value is calculated from

REGE5HEX = (VS / 133.3mV)*255

REGE4HEX and REGE5HEX are 8-bit values, so they range from 0 to 255. When their values are found, the same

values can be written to corresponding EEPROM addresses C4HEX and C5HEX. However, with SPI bus, the

address MSB in write operation is 0, so the addresses are actually 44HEX and 45HEX.

Example: Single capacitance sensor

CS MIN=8pF

CS MAX=12pF

CR = [8pF*12pF*(0.9-0.1)] / (12pF*0.9-8pF*0.1) = 7.68pF

REGE4HEX = (7.68pF/22pF)*255 = 89.0 ~ 89

VS = 100.8mV*)/(12pF-8pF)/(12pF*0.9-8pF*0.1)=40.32mV

REGE5HEX = (40.32mV/133.3mV)*255 = 77.1 ~ 77

REGE3HEX = 0 (no internal CS capacitor matrix used)

MAS6512 Datasheet(PDF) 23 Page - Micro Analog systems