UM0432 Datasheet, PDF(37/53 Page) STMicroelectronics – Low voltage motor control demonstration board

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UM0432 Datasheet, PDF (37/53 Pages) STMicroelectronics – Low voltage motor control demonstration board

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UM0432

Motor control operations

7.4.16

Changing the maximum allowed current level

An over-current protection mechanism is included inside the board to protect the system,

disabling all the power switches if the current that flows inside the motor is greater than a

given threshold. If this occurs, the red LED starts blinking. This mechanism is called

hardware current protection.

This threshold value is fixed by the hardware to 7.65 A. To change this threshold to IMAX, the

R77 resistor must be modified as per Equation 1 (changing the hardware current protection

threshold).

Equation 1

R77

------------------1---0----K-------------------

--------------5--------------- â 1

0.07 â¢ IMAX

When the BLDC (trapezoidal) driving strategy is used, there is another current protection

mechanism called software current limitation, which regulates the current that flows inside

the motor. In current mode, the current is regulated to a certain value, and in voltage mode

the current is limited to a maximum value.

The maximum current allowed by this mechanism is related to the hardware and is fixed at

6.5 A. To change this threshold, the R20 resistor must be modified as described below.

First, the amplification factor called AMP must be calculated using Equation 2 (amplification

factor).

Equation 2

AMP = --------------5---------------

0.07 â¢ IMAX

Then, the value of R20 can be calculated using Equation 3 (changing the maximum allowed

current).

Equation 3

R20 = (AMP â 1) â¢ 10K

After this modification, the "gui.ini" file must be modified. This file is inside the same folder

as the "LVST7MC - GUI" file.

Open the "gui.ini" file using the notepad tool and change the values of the following lines:

MAX_CURRENT = 8

â¦

AMP_SENS = 11

Replace the value 8 with IMAX expressed in amps and 11 with the AMP value calculated by

Equation 2.

Remember to close and re-open the "LVST7MC - GUI" file to activate this modification and

follow the instructions in Section 7.4.2.

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