Lc Sensor Metering Principle; Figure 13. Functional Block Diagram Of Lc Sensor Metering - ST STM32L073Z-EVAL User Manual

Hardware layout and configuration
7.20.1

LC sensor metering principle

Figure 13. Functional block diagram of LC sensor metering

The port PD7 of the microcontroller STM32L073VZT6 is configured in GPIO output to
deliver a high state. PD7 is in fact the signal called POWER_CONTROL. It is in charge to
provide power supply to the resistor divider Ra, Rb and the follower amplifier based on an
operational amplifier. The DC voltage at the output the operational amplifier is approximately
VDD/2 as Ra = Rb.
In a second phase, the port PB4 is used in GPIO output to cause a DC current flowing inside
the inductor of the LC sensor.
In steady state, the DC current is V
magnetic core.
PB4 is internally disconnected from the GPIO and connected to the positive input of the
comparator Comp2 of the microcontroller STM32L073VZT6. The current disruption causes
high frequency voltage self-oscillations of the LC resonator circuit. The lower connection of
the LC resonator is considered grounded from an AC point of view thanks to the capacitor
and the low output impedance of the follower amplifier. Then, the voltage oscillations are
32/64
/2 Re. The inductor stores the electrical energy in his
DD
UM1878 Rev 2
UM1878