The inputs configuration for half-step driving is shown in the Figure 4 (page 8) of the L6219 datasheet
To implement a microstepping driving, a variable voltage proportional to the desired output current must be applied to each of the reference pins (VREF1, VREF2). The the two inputs voltage are rectified sine-wave voltages with a phase delay of 90°.
The inputs configuration can be full-step driving or the half-step to improve the performance
at the zero crossover of the current.
The ST portfolio offers more advanced devices for microstepping operation, in the "Stepper Motor Drivers" product selector you can find the best fitting according your application requirements.
In particular, L6228 or STSPIN820 (device with voltage/current ratings closer to L6219) integrate the control logic for easier microstepping driving.
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