Norwood, Mass., USA: A novel packaging technology for digital isolators achieves a minimum of 8mm creepage distance required to ensure safe operation in high-voltage medical and industrial applications. Developed by Analog Devices, the CSA-certified package (which actually achieves 8.3mm creepage) is designed for systems that operate up to 220V to 250V ac.
Creepage is the shortest distance over an insulating surface, such as an IC package, over which an arc may travel between two galvanically isolated conductors. To ensure adequate insulation, a 125V working voltage needs 6mm of creepage, while a 220V to 250V working voltage requires a package with a minimum of 8mm. The JEDEC standard 16-lead SOIC has 7.6mm of creepage measured around the end of the package. Thus, it doesn’t meet the 220V to 250V ac requirements to ensure safe operation in high-voltage medical and industrial applications.
By increasing the length of the standard JEDEC package by 2.5mm, ADI could enlarge the creepage path to 8.3mm. The resulting package remains compatible with the JEDEC standard footprint, and there’s minimal impact on board space.
The new packaging technology employs ADI’s iCoupler digital isolation technology. As a result, designers can now replace lower performing optocouplers with its digital isolators, according to the company.
The iCoupler technology is based on chip-scale transformers, rather than on LEDs and photodiodes found in optocouplers. Transformers are said to support higher data rates, consume less power, and feature more stability over life compared to LEDs and photodiodes. By fabricating the transformers directly on-chip using wafer-level processing, iCoupler channels can be integrated with each other and other semiconductor functions at low cost. The transformers are planar structures formed from CMOS and gold metal layers.