FDC1004: Offset Calibration Registers format

Hi Jeff,

The measurement register's format is a little different than the offset calibration register's format. The capacitance measurement is a 24-bit two's complement value split between two 16-bit registers, MEASn_MSB and MEASn_LSB. MEASn_MSB[15:0] are the most significant 16 bits of measurement n. MEASn_MSB[15] is a sign bit because the value is in two's complement. MEASn_LSB[15:8] are the least significant 8 bits of measurement n, and MEASn_LSB[7:0] are reserved and are always 0. The measurement register is not split into an integer portion and a decimal portion like the offset calibration register.

Could you clarify what you mean by OoP mode? In general, you do not need to disable MEAS_4, though it is perfectly acceptable to do so. You may also set GAIN_CAL4 to 0 if you wish.

Regards,

Hello Jeff,

Decoding the FDC1004 measurement results is discussed in section 8.6.1.1 of the datasheet. The data is stored as 2s complement, not sign magnitude. The calculation is:
if measure_code > 2^23:
sensor_cap = ((measure_code - 2^24)/2^19 ) + Coffset
else
sensor_cap = (measure_code /2^19 ) + Coffset

The Measurement results are formatted in the same way as offset, but you should use the equation in the datasheet and add on the CAPDAC setting.

As for the second questions: if you do not configure a measurement, do not enable it; so 2A is yes.
The Gain Calibration is factory set as discussed in section 8.3.3.

Regards,

ChrisO