AN2009 datasheet(9/39 Pages) STMICROELECTRONICS

Part #	AN2009

Description	PWM MANAGEMENT FOR 3-PHASE BLDC MOTOR DRIVES USING THE ST7MC

PDF	39 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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PWM MANAGEMENT FOR 3-PHASE BLDC MOTOR DRIVES USING THE ST7MC

3.2 ST METHOD

With the ST Method, by using the free-wheeling diodes during the OFF time of the PWM

signal, the M potential is put to ground and the ST7MC microcontroller samples the BEMF

signal voltage during the OFF time of the PWM signal. This involves the fact that the PWM has

to be applied on the high side and that an OFF time is needed as explained in the next section

of this application note. However, fewer external components are required as it is no longer

necessary to divide and filter the signal coming from the non-powered winding. As shown in

Figure 6, only 3 external resistors are needed to limit the current input in the microcontroller

pins.

Figure 6. ST sensorless control Method

Low

Side

outputs

High

Side

outputs

ST7FMC

Rotor

position

inputs

internal

Vref

External

Vref

Level

Shifter

AN2009 Datasheet(PDF) 9 Page - STMicroelectronics