CS is the input to the current-sense comparators. The UCCx813-x current sense is significantly different from its predecessor. The UCCx813-x device family has two different current-sense comparators: the PWM comparator and an overcurrent comparator. The overcurrent comparator is intended only for fault sensing, and exceeding the overcurrent threshold causes a soft-start cycle. The earlier UC3842 family current-sense input connects to only the PWM comparator.
The UCCx813-x device 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, prevents false triggering due to leading edge noises which means that in most applications, no analog filtering (external R-C filter) is required on CS. Compared to an external RC filter technique, the leading-edge blanking provides a smaller effective CS-to-OUT delay. However, the minimum non-zero on-time of the OUT signal is determined by the leading-edge-blanking time and the CS-to-OUT propagation delay. The gain of the current sense amplifier is typically 1.65 V/V in the UCCx813-x family versus typically 3 V/V in the UC3842 family. Connect CS directly to MOSFET source current sense resistor.