UM0432 datasheet(40/53 Pages) STMICROELECTRONICS

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Motor control operations

UM0432

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The maximum current allowed by the GUI has been set to 8 A (see Section 7.4.8).

7.5.7

Stopping the motor (LED action)

Push the Start/Stop button to stop the motor. The LEDs toggle from green to red to indicate

an "idle" state.

7.5.8

Configuring the system for BEMF amplification

It is possible to configure the system to enable a BEMF amplification network. This

configuration can be useful in any circumstance where the BEMF signal is very low, such as

low speed for instance. This network can also compensate the free-wheeling diode voltage

drop, which is not negligible in the case of a low bus voltage value. See AN1103 "Improved

B-EMF detection for low-speed and low-voltage applications". Use the settings in Table 16

to enable this feature.

7.5.9

Detecting the BEMF during the PWM on time

The direct back-EMF sensing scheme used by default by the STEVAL-IHM015V1

demonstration board, synchronously samples the motor back-EMF during PWM "off" time

without needing to sense or reconstruct the motor’s neutral point in a sensorless BLDC

motor drive system. Since this direct back-EMF sensing scheme requires a minimum PWM

"off" time to sample the back-EMF signal, the duty cycle cannot reach 100%. Furthermore,

in some applications, that is, HVAC using high-inductance motors, the zero crossing

detection is unsymmetrical at high speeds. It has been noted that the long settling time of a

parasitic resonant between the motor inductance and the parasitic capacitance of power

devices causes false zero crossing detections of the back-EMF. In such cases, the back-

EMF detection during PWM "on" time can be used to solve the problem.

More information on this issue can be found in the application notes AN2030, AN1946 and

AN1103. The STEVAL-IHM015V1 demonstration board can be configured to detect the

BEMF during the PWM "on" time.

Sampling of the BEMF can be performed using three different references.

●

Internal reference (default configuration)

●

VBus/2 external reference

●

Reconstructed neutral point external reference.

Table 16.

BLDC SL with BEMF amplification jumper settings

Driving mode

Jumper setting

BLDC_3PH_SL

J11 between 2-3, J12 between 2-3, J13 between 1-2

J15 between 2-3, J16 between 2-3, J17 between 1-2

J18 between 2-3, J19 between 2-3, J20 between 1-2

J3 Closed, J4 variable (2-3)

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