Application information

AN4243

24/29

Doc ID 024199 Rev 1

3.3

Six-step driving method with BEMF zero crossing detection

To implement a sensorless motor control system, the information on rotor position is

achieved by BEMF zero-crossing detection; in this way, no hall-effect sensors or encoders

are needed.

In six-step driving mode one of the three phases is left in high-impedance state. Comparing

the voltage of this phase with the motor neutral point voltage (or star point) we can detect

the BEMF zero-crossing. This information about the commutation between two consecutive

steps allows the rotor synchronization to be achieved.

In the example of Figure 21, the OUT1 phase voltage is monitored by the CP+; the center-

tap voltage is obtained as combination of three phase voltages and monitored by the CP-

commutation each time a BEMF zero crossing is detected.

In this configuration one sense resistor is needed, the three OUT pins are connected

Figure 21.

Six-step with zero crossing detection typical application

EN3

CP+

CP-

GND

CPOUT

POWER

GROUND

SIGNAL

GROUND

+

-

VCP

VBOOT

SENSE

1

DIAG/EN

ENABLE

IN3

EN2

IN2

EN1

IN1

EN3

Zero Crossing

signal

IN3

EN2

IN2

EN1

IN1

SENSE

2

SENSE

3

THREE-PHASE

MOTOR

M

AM16583v1