The SS pin also fulfills the function of a restart
timer in an OVP event or following a DIR command change:
- Restart timer in OVP: When OVPA or OVPB catches an overvoltage event (refer to
Section 8.3.17), CSS is discharged immediately by the internal pulldown
FET. This FET remains ON as long as the overvoltage condition persists. When the
overvoltage condition is removed and after the SS voltage is discharged to below
0.23 V, the SS pulldown is released, setting off a new soft-start cycle. The
circuit can run in retry or hiccup mode if the overvoltage condition reappears.
The retry frequency is determined by the SS capacitor as well as the nature of
the overvoltage condition.
- Restart timer: When DIR dynamically flips its state from 0 to 1, or 1 to 0
during operation, CSS is first discharged to 0.23 V by the internal
pulldown FET. Then, the pulldown is released to set off a new soft-start cycle
to gradually build up the channel current in the new direction. In this way, the
channel current overshoot is eliminated.