AN1946 datasheet(9/35 Pages) STMICROELECTRONICS

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AN1946

The implemented resistors are used to limit the input current in the pad diode which clamps

the voltage on MCIA, MCIB and MCIC microcontroller inputs.

The current in the clamping diode should not exceed 5mA and should typically be around

2mA.

For a high voltage (400V) DC bus, 200k resistors are to be used. For safety and power dissi-

pation, two 100k resistors in serial are implemented on each phase.

Resistors implemented on the starter kit board are two 82k which is suitable both for the 24V

motor included and also for high voltage motors.

3.3 PRACTICAL RESULTS

The sampling below (Figure 8) shows the voltage signal on one phase of the motor drive in 6-

step mode.

During both steps where the phase is not energized, corresponding to the floating state of the

winding, we can follow the progression of BEMF:

For the "rising transition" between T1 & T2 where BEMF passes from a negative to

positive value;

For the "falling transition" between T4 & T5 where BEMF passes from a positive to

negative value.

We can note the PWM superposition with the BEMF signal for both "ON" and "OFF" states of

the PWM.

For compare values set to zero, we get the zero crossing information only when the PWM is

in an "OFF" state.

AN1946 Datasheet(PDF) 9 Page - STMicroelectronics