5
https://eckstein-shop.de/
rates, but the current must actively be limited to under 1 A to prevent damage to the
motor.
The DRV8825 supports such active current limiting, and the trimmer potentiometer on
the board can be used to set the current limit. You will typically want to set the driver’s
current limit to be at or below the current rating of your stepper motor. One way to set
the current limit is to put the driver into full-step mode and to measure the current
running through a single motor coil without clocking the STEP input. The measured
current will be 0.7 times the current limit (since both coils are always on and limited to
approximately 70% of the current limit setting in full-step mode).
Another way to set the current limit is to measure the voltage on the “ref” pin and to
calculate the resulting current limit (the current sense resistors are 0.100Ω). The ref pin
voltage is accessible on a via that is circled on the bottom silkscreen of the circuit board.
The current limit relates to the reference voltage as follows:
So, for example, if you have a stepper motor rated for 1 A, you can set the current limit
to 1 A by setting the reference voltage to 0.5 V.
Note: The coil current can be very different from the power supply current, so you
should not use the current measured at the power supply to set the current limit. The
appropriate place to put your current meter is in series with one of your stepper motor
coils.
POWER DISSIPATION CONSIDERATIONS
The DRV8825 driver IC has a maximum current rating of 2.5 A per coil, but the current
sense resistors further limit the maximum current to 2.2 A, and the actual current you
can deliver depends on how well you can keep the IC cool. The carrier’s printed circuit
board is designed to draw heat out of the IC, but to supply more than approximately
1.5 A per coil, a heat sink or other cooling method is required.
