UM0522
Motor control operations
31/39
At this point the system is ready to run. If the hardware current limitation set by default for
this board (8 A) has to be modified, go to next paragraph, otherwise it is possible to skip to
paragraph
Section 8.16: Driving the BLDC motor (trapezoidal - sensorless) on page 32
8.15
Changing the maximum current level allowed
An overcurrent protection mechanism is included inside the board that protects the system,
disabling all the power switches if current that flows inside the motor is greater than a certain
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 8 A.
To change this threshold to I
MAX
(expressed in A), resistor R51 (expressed in k
Ω
) must be
modified according to equation
.
Equation 1:
For example if the desired threshold is 2.2 A it is required to use R
51
=200k
Ω
.
Note:
A place holder named R53 in parallel to R51 is also included that can be useful if the
calculated value is not a standard value resistor. In this case it is possible to get better
accuracy using two standard value resistors in parallel to get the calculated value.
For a lower value of current threshold, in order to avoid noise on current feedback, the shunt
resistor R10 may be reduced, in which case the formula that should be used is equation
:
Equation 2:
If R51 and/or R10 are changed, the "gui.ini" file must be modified. This file is stored in the
same folder as the "STEVAL-IHM017.01 - GUI" file.
First calculate the Amplification factor using equation
Equation 3:
Open the "gui.ini" file using the notepad and change the value of the following line:
MAX_CURRENT = 4.4
…
AMP_SENS = 5.6
R_SENS = 0.1
Replace the value 4.4 with I
MAX
expressed in amps, the value 5.6 with the A value
calculated by equation
, and 0.1 with the value of R10.
R
51
450
I
MAX
------------
K
Ω
=
R
51
45
I
MAX
R
⋅
10
-----------------------------
K
Ω
=
A
R
51
10K
Ω
---------------
=
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