User manual

F1 LV Evaluation Platform Motor Control Add-Ons
DS41629A-page 44  2012 Microchip Technology Inc.
5.3.5 Protection
Two 5A fuses (F1 and F2) are used to protect your add-on in case of an overcurrent
situation of the supply voltage. In case one or both of them get burnt, remove power
immediately from the board and inspect the add-on for further damage. Do not replace
the burnt fuses with other values than the ones provided with the board.
5.3.6 UNI/O
®
Memory Chip
The UNI/O
®
memory chip stores the board ID and the application parameters. It is
accessed by the Motor Control GUI at start-up in order to recognize which of the four
motor control add-on boards had been attached to the F1 LV Evaluation Platform, thus
loading the appropriate parameters for the add-on used.
5.3.7 Speed Control
Speed control can be performed through either the Motor Control GUI or the 10K POT
R4 located on the F1 LV Evaluation Board.
5.3.8 Current Control
The demo software is intended for control without an actual current feedback. However,
by reading the voltage level on shunt resistor R3, you can implement a software
overcurrent protection and perform current control.
For example, a chopper circuit, perhaps the most used method of current control in
motor control drives, can be emulated just by using PIC MCU
modules. The
PIC16LF1947 has a Fixed Voltage Reference of 1.024V selectable as an input to the
internal 5-bit DAC, which in turn can be used by the internal comparators as a reference
on the positive inputs. If we select the minimum 1/32 step in the DAC we obtain a
comparator trigger level of 32mV, which is sufficient to chop the current to the motor in
order to maintain it under its maximum rating given by the motor manufacturer (1A in
the case of the Leadshine unipolar stepper).
The Enhanced Capture/Compare/PWM modules have built-in features in PWM mode
for automatically shutting down the PWM if the comparators are triggered and
auto-restarting the PWM if certain conditions are met (please consult the PIC16LF1947
data sheet to learn more).
By adjusting the values of the shunt resistors accordingly, you can emulate the chopper
circuitry, thus reducing the costs of external components and saving up precious space
on your board.
Figure 5-2 below gives an insight on how to use the PIC MCU modules as parts of a
current chopper: