AN2267

BLDC motor control using ST7FMC

5/19

3

BLDC motor control using ST7FMC

The main feature of ST7FMC is its powerful motor control macro cell, capable of generating

control signals to drive a sensorless or sensored 3 phase BLDC or AC motor.

STMicroelectronics application notes AN1946 [1] and AN2030 [2] explain, in detail, the

procedure to control a 3 phase BLDC motor using ST7FMC.

Figure 5 shows the simplified block diagram of the hardware motor control macro cell. The

macrocell has multiple timers performing various functions in parallel to generate control

pulses for the motor. An auto scalable 8-bit timer (MTIM) monitors the time difference

between successive phase back EMF zero crossings (Z events) of the motor. When a Z

event occurs, the timer value is captured into MZREG and the timer restarts counting from

zero, and, the previous content of MZREG is transferred to MZPRV. This timer is a part of

what is called DELAY MANAGER that, based on this time difference and a delay coefficient

(MWGHT), identifies the timing for next phase commutation instant (C events). All in

parallel, a 12-bit free running counter generates the PWM carrier for inverter switching.

Figure 5.

Simplified block diagram of Motor control Macro cell for BLDC motors

MCI

MCI

MCI

BEMF=

MCO

MCO

MCO

MCO

MCO

MCO

DELAY = WEIGHT x

MCCFI

MCCRE

NMCE

COMMUTE

In

(I

(V

C

(I

DELAY

CHANNEL

BEMF ZERO-CROSSING

PWM

[Z

(V

[Z] : Back EMF Zero-crossing

[C] : Commutation

C

(I): Current

(V): Voltage

U, V,

Phase

Phase

INPUT DETECTION

12-bit THREE-PHASE

PWM GENERATOR

MCVRE

MCAO

MCAO

MCPWM

MCPWM

MCPWM

(V

PCN

MCAOZ/

OAON

+

-

CFAV

AD

TACH

or SPEED MEASURE UNIT (not

=

Ex

Vre

WEIGH

CAPTURE

MTI

TIME

Encoder

MEASUREMENT

WINDOW

GENERATOR

MOD

CURRENT

VOLTAGE

P

H

A

S

Phase

Phase W

Phase V

12-bit

Vdd