AN2009 Datasheet, PDF (1/39 Pages) STMicroelectronics – PWM MANAGEMENT FOR 3-PHASE BLDC MOTOR DRIVES USING THE ST7MC

AN2009
APPLICATION NOTE
PWM MANAGEMENT FOR
3-PHASE BLDC MOTOR DRIVES USING THE ST7MC
INTRODUCTION
The ST7MC microcontroller family is the second generation of the 8-bit microcontroller family
dedicated to the driving of 3-phase brushless motors. Permanent Magnet Brushless DC mo-
tors are replacing DC brush motors more and more in many applications due to advantages
such as higher efficiency, quieter operation and better reliability. These motors require the
control of an inverter stage. In most cases the switching devices are MOSFET transistors or
IGBTs and are organized in a three-phase bridge with free-wheeling diodes as shown in
Figure 1. There are two methods of controlling the motor and reading information back from
the rotor. These are called the sensor and the sensorless methods. The sensor method uses
Hall sensors whereas the sensorless method reads the Back Electromotive Force (BEMF)
signal back to determine the position of the rotor and so is less expensive.
The ST7MC microcontroller features a dedicated peripheral to drive this type of motor with the
best efficiency in order to maintain the advantages of these types of motor. Besides the high
flexibility of this dedicated peripheral, its high hardware integration allows cost savings for the
application by reducing external components. It is suitable for both sensor and sensorless
methods of PM BLDC motor control.
Although using the sensorless mode has big advantages in terms of cost and size, it makes
the motor drive a little more complicated. The purpose of this application note is to explain in
which cases the ST7MC motor control unit can directly read the BEMF voltage and how to
quickly set up its control registers in order to use all the advanced features of this product. We
will detail and explain the PWM management inside the ST7MC in order to help the developer
use all the advantages of this flexibility to optimize the design and the efficiency of the appli-
cation.
AN2009
Rev 2
1/39
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