The TPSM8A28 and TPSM8A29 devices monitor a resistor-divided feedback voltage to detect overvoltage and undervoltage events. When the FB voltage becomes lower than 80% of the V_INTREF voltage, the UVP comparator detects and an internal UVP delay counter begins counting. After the 68-µs UVP delay time, the device enters Hiccup mode and re-starts with a sleep time of 14 ms. The UVP function enables after the soft-start period is complete.

When the FB voltage becomes higher than 116% of the V_INTREF voltage, the OVP comparator detects and the circuit latches OFF the high-side MOSFET driver and turns on the low-side MOSFET until reaching a negative current limit I_NOCL. Upon reaching the negative current limit, the low-side FET is turned off, and the high-side FET is turned on again for a proper on time (determined by V_IN/V_O/f_SW). The device operates in this cycle until the output voltage is pulled lower than the UVP threshold voltage for 68 µs. After the 68-µs UVP delay time, both the high-side FET and the low-side FET are latched OFF. The fault is cleared with a reset of VIN or by retoggling the EN pin.

During the 68-μs UVP delay time, if output voltage becomes higher than the UV threshold, thus it is not qualified for the UV event, the timer is reset to zero. When the output voltage triggers the UV threshold again, the timer of the 68 μs re-starts.