How Does MagSense Work?
Cypress’ PSoC 4700 MCUs provide support for MagSense inductive-sensing. This figure shows the inductive-sensing system using a PSoC 4700 MCU. A capacitor, C, is placed in parallel with the coil to create a parallel LC “tank”. The tank has a resonant frequency provided by the following equation: f_0= 1/(2π √LC)
The frequency of the Lx GPIO (sensor excitation pin) is set to the resonant frequency of the tank (f0). The pin drives the tank circuit through a resistor, RLX. The impedance of the tank circuit is the maximum at the resonant frequency, so a significant sinusoidal component with amplitude VAMP (peak) appears across the tank circuit. This signal is AC-coupled into the Amplitude to Digital Converter through the capacitance Cc and is then converted into equivalent raw counts. A change in inductance of the LC tank causes a change in VAMP resulting in a change in the raw count of corresponding channels.
PSoC 4700 MCU MagSense Inductive-Sensing System
This system has the advantage that it excites the tank circuit to a know frequency. Multiple tank s can be set to resonate at different frequencies. Also, the frequency of operation of the tank circuit is controlled and can be designed for robust EMC performance. The practical coil impedance is represented as an Inductance (L) with a series resistor (Rs).
LC Tank Resonance Circuit
To find out more, checkout the Inductive Sensing Design Guide.