8.4.18 Brownout

The UCD90320U device triggers brownout event when the V33D pin voltage drops below the brownout threshold voltage, (V_BOR). During a brownout event, the device continues to write fault logs into the EEPROM that occurred before the brownout event. As the supply voltage continues to drop, the device fully shuts down when the V33D pin voltage is below the shutdown threshold voltage (V_SHDN). Any fault event that has not been written into the EEPROM before the device shutdown is lost.

In the scenario where several faults happen immediately before the brownout event, the device requires a capacitance of 500 µs in order to write the first fault event into the EEPROM. The write function requires an additional 4 ms to write the Black Box fault log into the EEPROM. Therefore, in order to preserve at least the first fault log, user must provide enough local capacitance to maintain the V33D rail above VSHDN for 500 µs (or 4.5ms with the Black Box fault log). Longer holdup time allows more fault events to be written into the EEPROM during brownout.

Figure 36. Reset and Brownout Thresholds