13/35

AN1946

Advantages

With the classical method, BEMF sampling is done during the PWM “ON” state allowing up to

a maximum PWM duty cycle (100%).

Drawbacks

Due to the voltage divider being used to sense BEMF, this method is less sensitive that the ST

method. This sampling method is dependent on the motor speed because the different net-

works are influenced by BEMF levels and components are to be dimensioned according to the

nominal operation point of the motor.

4.2 PRACTICAL IMPLEMENTATION OF SAMPLING DURING PWM ON

The starter kit board is delivered with a daughter board allowing classical sampling method

use.

Figure 12 gives an example of network use to implement the classical method with an analog

filter.

Figure 12. Classical method of implementation with daughter board.

R5

R3

R1

R10

C1

C2

C3

C4

MCVREF

MCIA

ST7FMC

Three

Phase

Power

Converter

V

U

W

6_MCOx

Motor

MCIB

MCIC