DRV8873: For unipolar stepper

Hirotaka-san,

DRV8873 uses high side FET to do current mirror for Output Current Sensing: IPROPIx and current-chopping.
If the unipolar stepper's center tape is connected to VM as your drawing, we will see:
1. Current chopping or regulation is disabled due to current sensing on high-side FET only.
2. Only slow decay is available if the unipolar stepper's center tape is connected to VM
3. OCP works because it monitors all FETs and the FET's Vds is positive at the winding current rising edge
4. IPROPIx doesn't work because the current flows from OUTx to VM, not VM to OUTx when high-side FET is on.

If the unipolar stepper's center tape is connected to ground (change "VM" to ground on the motor connection), current regulation and IIPROPIx will work.

For the attached file questions:
1. So, using this construcution×2(DRV8873×2), is it possible to configure unipolar stepping driver?
Yes. But, to let current regulation and IPROPIx work, please change the unipolar stepper's center tape connection from "VM" to ground.

2. We guess that it is impossible to use OCP function, because current doesn’t flow high-side FET’s.
OCP works because it monitors all FETs and the FET's Vds is positive at the winding current rising edge