AN2459 - Application note

Signals measurement, processing & control

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4.4

MOSFET current measurement

The main reason for measuring a current flowing through the PFC MOSFET is to prevent

exceeding the maximum current rating and so saturating the boost inductor which results in

damaging components.

The software routines in general are too slow to perform fast reaction. For this reason, only

hardware peripherals are used, and the software is excluded from the detection of over-

current. Two extra features of the ST7LITE19B are important for this protection:

●

the analog comparator;

●

the break function.

The comparator integrated inside the microcontroller (datasheet ST7Lite1xB, 4 section 11.6)

is a general purpose analog comparator with either an external or internal reference. Output

can be seen on an external pin (Port PA7 - pin 11), or as it is in this case used only internally

as an input for the second peripheral - the Break.

The Break function is an emergency shutdown used to stop all PWM outputs (i.e. MOSFET

gate signals). A detailed description of it may be found in the ST7FLITE19B datasheet, 4

section 11.2.3.3.