AN1946 datasheet(21/35 Pages) STMICROELECTRONICS

Part #	AN1946

Description	SENSORLESS BLDC MOTOR CONTROL AND BEMF SAMPLING METHODS WITH ST7MC

PDF	35 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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AN1946

Advantages

This method of BEMF sampling is done during PWM “ON” state allowing up to a maximum

duty cycle (100%). Use of high frequency sampling without analog filtering and with the possi-

bility of digital filtering gives more flexibility to this method.

Drawbacks

This method is less sensitive than the ST method because the voltage divider is used to sense

BEMF.

5.2 PRACTICAL IMPLEMENTATION

The following schema shows the network for sampling during PWM ON using a digital filter im-

plemented with the use of an external reference voltage following the DC bus variation.

The network on the DC bus used to realize the reference voltage can be removed in the situ-

ation where the DC bus is constant.

In its place we use the internal programmable reference (from 0.2V to 3.5V) of the ST7MC.

Figure 21. Digital PWM ON Sampling Implementation

R10

Three

Phase

Power

Converter

VDC

Motor

MCVREF

MCIA

ST7FMC

6_MCOx

MCIB

MCIC

AN1946 Datasheet(PDF) 21 Page - STMicroelectronics