7.3.3 Measuring Inductance With LDC1001

LDC1001 measures the sensor’s frequency of oscillation using a frequency counter. The frequency counter timing is set by an external clock applied on TBCLK pin. The sensor frequency can be calculated from the frequency counter register value (see registers 0x23 through 0x25) in Equation 3:

Equation 3.

where

• ƒ_SENSOR is the measured sensor frequency
• ƒ_EXT is the frequency of the external clock.
• FCOUNT is the value obtained from the Frequency Counter Data registers (address 0x23,0x24,0x25).
• RESPONSE_TIME is the programmed response time (set in the LDC configuration register, address 0x04).

Use Equation 4 to determine the sensor inductance:

Equation 4.

where

• C is the parallel sensor capacitance
• ƒ_SENSOR is the sensor frequency calculated in Equation 3

Example: If ƒ_EXT = 6MHz, RESPONSE_TIME = 6144, C = 100 pF and measured Fcount = 3000 (dec) (address 0x23 through 0x25)

ƒ_sensor=(1/3) × (6000000/3000) × (6144)= 4.096 MHz

Using the ƒ_sensor = 4.096 MHz example for Equation 4, the sensor inductance L = 15.098 µH.