This application note reviews sensor RP configuration for LDC devices. LDC1000, LDC1041, LDC1051, LDC1312, LDC1314, LDC1612, LDC1614 are covered in this note. Clear understanding on how to set the RP_MIN and RP_MAX registers is necessary for not only RP measurements, but also for optimum L measurements.
The fundamental principle of RP measurements is that magnetic fields from an LC circuit generate eddy currents on the surface of nearby conductive materials. These currents appear as additional parasitic resistance in the LC circuit. The energy dissipated as heat due to this resistance will be lost, and LDC devices can measure this loss. The amount of parasitic resistance generated by eddy currents is a function of the inductor shape, distance between inductor and conductive target, temperature, and the target composition.
RP configuration is quite different for LDC10xx devices and LDC13xx/16xx devices.
• While the LDC131x and LDC161x devices do not measure RP, they still need to be configured to accommodate the change in RP as the target moves. Due to the different architecture between the LDC10xx family of devices and the LDC131x and LDC161x devices, the process is different.
• LDC10xx devices use RP_MIN and RP_MAX settings to determine minimum and maximum amount of energy inserted into the resonator. The converters are also able to measure the amount of energy dissipated at each point of time. Therefore, resistive losses can be determined and proximity values are used as the output.
LDC13xx/16xx devices use only one register setting, represented as drive current, to configure the maximum amount of energy inserted into the resonator. The current drive is usually constant during normal operation.