I am driving a bipolar hybrid stepper motor rated 1A with a DRV8825 at 12 V.
About current regulation the datasheet says:
184.108.40.206 Current Regulation
In a stepper motor, the set full-scale current (IFS) is the maximum current driven through either winding. This quantity depends on the xVREF analog voltage and the sense resistor value (RSENSE). During stepping, IFS defines the current chopping threshold (ITRIP) for the maximum current step. The gain of DRV8825 is set for 5 V/V.
To achieve IFS = 1.25 A with RSENSE of 0.2 Ω, xVREF should be 1.25 V.
In my circuit, RSENSE is 0.1 Ω. Following, in order to get IFS of 1.0 A, xVREF should be 0.5 V.
However, when I set the reference voltage to 0.5 V, I can measure only 0.5 A in both windings in full-step mode. Through experimentation I found that I get 1.0 A with a reference voltage of 1 V - which should give 2 A following the equation above.
On page 4, the datasheet says the VREF input voltage should be 1 - 3.5 V with the following note:
(2) Operational at VREF between 0 to 1 V, but accuracy is degraded.
Can it really be so inaccurate just slightly below 1 V, or am I getting something wrong here?