The UCC280x devices feature undervoltage lockout protection circuits for controlled operation during power-up and power-down sequences. Both the supply voltage (VCC) and the reference voltage (Vref) are monitored by the UVLO circuitry. An active low, self-biasing totem pole output during UVLO design is also incorporated for enhanced power switch protection.

Undervoltage lockout thresholds for the UCC2802, UCC2803, UCC2804, and UCC2805 devices are different from the previous generation of UCx842, UCx843, UCx844, and UCx845 PWMs. Basically, the thresholds are optimized for two groups of applications: off-line power supplies and DC-DC converters.

The UCC2802 and UCC2804 feature typical UVLO thresholds of 12.5 V for turnon and 8.3 V for turnoff, providing 4.3 V of hysteresis.

For low voltage inputs, which include battery and 5-V applications, the UCC2803 and UCC2805 turn on at 4.1 V and turn off at 3.6 V with 0.5 V of hysteresis.

The UCC2800 and UCC2801 have UVLO thresholds optimized for automotive and battery applications.

During UVLO the IC draws approximately 100 μA of supply current. Once crossing the turnon threshold the IC supply current increases typically to about 500 μA, over an order of magnitude lower than bipolar counterparts.

Figure 9-1 IC Supply Current at UVLO