SLUSEV2C June 2022 – March 2023 UCC28C50-Q1 , UCC28C51-Q1 , UCC28C52-Q1 , UCC28C53-Q1 , UCC28C54-Q1 , UCC28C55-Q1 , UCC28C56H-Q1 , UCC28C56L-Q1 , UCC28C57H-Q1 , UCC28C57L-Q1 , UCC28C58-Q1 , UCC28C59-Q1
PRODUCTION DATA
An external series resistor (RCS) senses the current and converts this current into a voltage that becomes the input to the CS pin. The CS pin is the noninverting input to the PWM comparator. The CS input is compared to a signal proportional to the error amplifier output voltage. Calculate the current sense resistor based on the 2.2-A peak magnetizing current at PO_MAX of 48 W.
For any input voltage, if the output is shorted to ground or the output voltage ramps up quickly during soft-start, the controller duty cycle can easily reach the maximum duty cycle (DMAX), so the power rating of the RCS resistor(s) must maintain adequate design margin to support those transient events.
The applications schematic shows two 0.91-Ω resistors that are 2010 size in parallel, R24 and R25, for a combined resistance of 0.455 Ω. Each can handle 0.55 W at 105°C ambient and 1 W below 70°C ambient. For a traction inverter at 105°C ambient, the two paralleled resistors can handle the worst case and offer enough margin from resistor mismatch.