50 V Isolation, 100 MHz, 50 mW Single-Chip Junction Isolated DC-DC Converter with Self-Tuned Maximum Power Transfer Frequency

A fully-integrated, point-of-load, low noise, isolated DC-DC converter for supply regulation of high dynamic range analog and mixed-signal isolated sensor signal-chains is presented. The isolated DC-DC converter utilizes an integrated planar air-core micro-transformer as a coupled-resonator and an isolation barrier, and enables direct connection of low-voltage mixed-signal circuits to higher supply rails for current and voltage sensing. The transformer is driven at its resonant frequency of 100 MHz to achieve maximum power transfer. A mixed-signal perturb-and-observe based frequency search algorithm is developed to improve maximum power transfer efficiency by 60% across the isolation barrier compared to fixed driving frequency method. The switching ripple at output is reduced by 11 dB utilizing spread spectrum clocking in the driver, and 21 dB using a low-dropout regulator. Conducted and radiated EMI distribution on the IC is measured by a set of proposed ring oscillator based noise sensors with -68 dBm noise sensitivity. The proposed isolated converter achieves the highest level of integration compared to state-of-the-art integrated isolated converters, and provides 50 V on-chip junction isolation using standard CMOS technology.