Current, and what limits it
R1 and R2 are fitted at 0 Ω, which turns off the DRV8833's current regulation. What is left setting the current is the supply and the winding, a continuous rating of 1.5 A per bridge, and an overcurrent trip that uses neither.
What 0 Ω switches off
The DRV8833 can regulate current. It measures the voltage across a sense resistor on each channel, and when that reaches 200 mV it switches the drive off until the next cycle of its own 50 kHz clock. The resistor's value sets the current.
R1 and R2 on this board are 0 Ω, so the voltage never gets there and the regulation never acts. TI's advice for a design that does not want it is to tie those pins to ground, which is what the 0 Ω links do.
For a DC motor this is what you want
A DC motor draws what its load makes it draw. There is little useful for a current limit to do, and VM sets the speed in the way anybody expects.
For a stepper it is the design constraint
A stepper coil held still is a resistor as far as the driver is concerned. The current is VM divided by the winding resistance plus the bridge's own resistance, about 0.36 Ω for one high-side and one low-side switch at 5 V.
That makes the supply voltage a per-motor decision. Match VM to the motor's rated voltage; a 5 V stepper on a 10.8 V supply takes more than twice its rated current, holds position hot, and gains nothing for it.
The two limits the chip does have
1.5 A per bridge, continuously. That is the datasheet's figure for the package on this board, with 2 A peak, at VM 5 V and 25 °C, with its thermal limits respected. Below 5 V the switches' resistance rises and the figure falls. It assumes the heat can get away, and this small board's copper is what decides how close you get. Nothing on the chip stops you going past it short of thermal shutdown.
The overcurrent trip, somewhere between 2 and 3.3 A. It does not use the sense circuitry, so the 0 Ω links do not remove it. It switches off the bridge that tripped, holds FLT low for 1.35 ms, and tries again. That is protection against a short or a hard stall, not a rating to run at, which reaches you as a buzz, a twitch, and a fault pin nobody wired up — unless you did.
When it does not work
There is nothing to trim. Current regulation needs sense resistors, this board fits 0 Ω in their place, and the feature is off in copper rather than in configuration. Set the current by choosing VM to suit the motor.
An A4988 regulates coil current to a level you set, and this board does not regulate it at all. At the same supply voltage the same stepper will draw more here. Lower VM until the current matches the motor's rating.
Between the 1.5 A continuous figure and the 2 A bottom of the trip band nothing on the chip limits current, so it heats. If it reaches thermal shutdown it switches its outputs off and pulls FLT low, and starts again once it has cooled. Lower VM, or use a motor that draws less.
The specs, the pin table and the short answers, in one place — for when you know the board and want the number rather than the explanation.
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