9.3.1.3 CS

CS is the PWM comparator and an overcurrent comparator. The UCC280x-Q1 family contains digital current sense filtering, which disconnects the CS terminal from the current sense comparator during the 100-ns interval immediately following the rising edge of the OUT pin. This digital filtering, also called leading-edge blanking, means that in most applications, no analog filtering (RC filter) is required on CS. Compared to an external RC filter technique, the leading-edge blanking provides a smaller effective CS to OUT propagation delay. Note, however, that the minimum non-zero on-time of the OUT signal is directly affected by the leading-edge-blanking and the CS to OUT propagation delay. The overcurrent comparator is only intended for fault sensing, and exceeding the overcurrent threshold causes a soft-start cycle.

The UCC280x-Q1 current sense is significantly different from its predecessor. The UC3842 family current sense input connects to only the PWM comparator. The UCC280x-Q1 current sense input connects to two comparators: the PWM comparator and the overcurrent comparator. Internal leading edge blanking masks the first 100 ns of the current sense signal. This may eliminate the requirement for an RC current sense filter and prevent false triggering due to leading edge noises. Connect CS directly to MOSFET source current sense resistor. The gain of the current sense amplifier on the UCC280x-Q1 family is typically 1.65 V/V versus typically 3 V/V with the UC3842 family.