MTD1120F stepper motor control circuit

MTD1120F four-phase stepper motor driver is shown in Figure 5 12.
The output power stage of this chip is composed of four Darlington transistors and some freewheeling diodes.
The transistor withstand voltage V_-80V, please pay attention to adding a zener when using it. Diode y for protection
. Logic power supply Vcc is commonly used 5v.
    The chopper current control here is slightly different from that of MT D2003F. Use a monostable circuit to replace
the RS trigger circuit. When the phase current rises to a predetermined value, it turns off and triggers the monostable circuit. After a
constant time TrwF, the phase winding is reconnected. TOFF is decided by external R. and CT.
    TOFF=0. 69GR.
    The phase current is determined by the reference electromagnetic field REF and the sampling resistor R.
    ,V.EF
    I=hundred