1 Introduction

Smaller DC/DC bias supplies, such as IIB modules with small component footprint and high-power density are becoming more in demand in numerous applications. IC level transformers with remarkable isolation technologies using high frequency power conversion are the main technology drivers enabling smaller IC packages and higher power density. UCC33xx0-Q1 family of devices is part of this trend with its ultra-small 4x5x1- $\mathrm{m}{\mathrm{m}}^3$ package and 64MHz switching frequency.

In order to deliver the power from the primary to the secondary side, UCC33xx0-Q1 use a burst frequency in the range of 100-500kHz depending on the load condition. The burst frequency can be explained as low frequency buckets and within these buckets, the device switches at a high frequency of 64MHz.

Proper setup for CE and RE is crucial to keep emissions below the limits. A tightly coupled connection must be present to connect the LISNs to the DUT. The switching frequency 64MHz is next to the VHF band for CISPR25 CE and RE and to mitigate emissions at this frequency, a HF pi filter using a 2xDM inductor was designed. The HF harmonics of the fundamental 64MHz is present in the 30-200MHz RE when using a Logarithmic Periodic Antenna (LPA). In this case two ferrite beads (FB) were selected to mitigate these frequencies. Finally, a proper layout using PCB Faraday shield, Keep Out Zone (KOZ), copper cut below DM inductors and FB and proper distribution of the ground planes helped to keep the switching frequency and its harmonics below the limits.

CISPR25 class 5 is the most stringent EMI standard for automotive applications.