SNVSBJ0A December 2019 – June 2020 LM5170
The SS pin also fulfills the function of a restart timer in an OVP event or following a DIR command change:
(1) Restart Timer in OVP: When OVPA or OVPB catches an overvoltage event (refer to Overvoltage Protection (OVPA, OVPB)), CSS is discharged immediately by the internal pulldown FET, and 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 may 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.
(2) 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.