18.4 An 11MHz Fully Integrated 5kV Isolated DC-DC Converter Without Cross-Isolation-Barrier Feedback
Lisong Li, Xiangming Fang, Rongxiang Wu
Abstract
Galvanic isolation greatly enhances system safety and reliability in applications such as medical devices and sensor interfaces. In these applications, space restriction is stringent and full integration is preferred. Several galvanically isolated power-transfer systems using on-chip capacitors or micro transformers have been reported [1]-[4]. In [1], isolated power transfer is achieved with on-chip capacitors, which are CMOS compatible. However, an off-chip inductor is needed in the power link. In addition, it is difficult for an on-chip-capacitor-based power-transfer system to achieve high isolation voltage and high output power at the same time with a reasonable silicon area. Coreless-micro-transformer-based power-transfer systems [2]-[3] operate at 160 to 330MHz with coil inductance of 10s of nH. It is very difficult to boost the efficiency at such high operation frequency. Meanwhile, the high-frequency operation also poses challenges to electromagnetic interference (EMI) control. A magnetic-core-micro-transformer-based power-transfer system can operate at 16 to 25MHz [4]. However, such a transformer is bulky and complex. Cross-isolation-barrier feedback devices are usually used for output regulation [1], [3], [4]. However, these devices take up additional space and increase packaging complexity for fully integrated power transfer systems. In this work, a fully integrated galvanically isolated DC-DC converter is presented. With a high-performance coreless micro transformer [5], a leakage-inductance-resonant flyback (LiRF) topology is proposed and the switching frequency is reduced to 11MHz. By adopting an energy-storing-capacitor-based controller, the output voltage (VO) can be regulated without a feedback device across the isolation barrier.