8.3.15.1 Failsafe OVP - Output Over-voltage Protection

Failsafe OVP prevents any single failure from allowing the output to boost above safe levels. Redundant paths for output voltage sensing provide additional protection against output over-voltage. Over-voltage protection is implemented through two independent paths: VSENSE and HVSEN.

VSENSE pin voltage is compared with two levels of over-voltage. If the lower one, V_{LOW_OV},is exceeded the COMP pin is discharged by an internal 2-kΩ resistance until the output voltage falls below V_{LOW_OV} reduced of 2% to provide hysteresis (ΔV_{LOW_OV_HYST}). If also the higher over-voltage threshold is exceeded in addition to activate the 2-kΩ pull down switching is soon disabled. In order to re-enable the switching the sensed voltage has to fall below V_{LOW_OV} reduced of 2%. Additional over-voltage protection can be implemented on HVSEN pin through a separate resistor divider to monitor output voltage. An over-voltage is detected if HVSEN pin voltage exceeds V_{HV_OV_FLT} an as consequence device stops switching and the 2-kΩ pull down is activated. The pull down 2-kΩ pull down is removed only if HVSEN pin goes below V_{HV_OV_CLR} threshold and the COMP pin is fully discharged to 20 mV. Both conditions needs to be true before the soft-start can begin.

The converter shuts down if either input senses a severe over-voltage condition. The output voltage can still remain below a safe limit if either sense path fails. The device is re-enabled when both sense inputs fall back into their normal ranges. At that time, the gate drive outputs will resume switching under PWM control. A low-level over-voltage on VSENSE does not trigger soft-start, an higher-level over voltage on VSENSE additionally shuts off the gate-drive outputs until the OV clears, but still does not trigger a soft-start. However, an over-voltage detected on HVSEN does trigger a full soft-start and the COMP pin is fully discharged to 20 mV before the soft-start can begin.