UM0432
Motor control operations
37/53
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 I
MAX
, the
R77 resistor must be modified as per
Equation 1
(changing the hardware current protection
threshold).
Equation 1
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
Then, the value of R
20
can be calculated using
Equation 3
(changing the maximum allowed
current).
Equation 3
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
…
AMP_SENS = 11
Replace the value 8 with I
MAX
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
.
R
77
10K
5
0.07
I
MAX
•
------------------------------
1
–
---------------------------------------------
=
AMP
5
0.07
I
MAX
•
------------------------------
=
R
20
AMP
1
–
(
)
10K
•
=
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