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
The input capacitors must be rated for the maximum input voltage, limit the input voltage ripple, and support the required RMS current. The primary peak current (IM_VIN) and duty cycle (DVIN) at any input voltage (VIN) can be derived with the following equations
The minimum input capacitance (CIN_MIN) and RMS current (ICIN_RMS) they must support can be estimated with the following
Assuming 30% input voltage ripple for both 20 W at 40-V and 40 W at 125-V, the required minimum input capacitance is calculated for each case based on the above equations. CIN_MIN at 40-V input is 1.15 µF, while CIN_MIN at 125-V input is only 0.24 µF.
Low voltage operation requires almost 5x more input capacitance to produce the same percentage of input voltage ripple. If the input of auxiliary power supply is tapped to the input of the system power converters, such as the back-up power supply of traction inverters, the input capacitance of the power converters may be sufficient to meet the CIN_MIN requirement at 40-V input. Therefore, the design example only parallels 2-3 high-voltage film capacitors near the regulator for high frequency decoupling.