In embedded applications that use the PC architecture, the USB interface has supplanted RS-232 for remote control, diagnostics, firmware updates, configuration of operational settings, and data exchange. As with its predecessor, one drawback to USB in medical and certain industrial applications is the lack of a provision for isolation in the basic standard, though mains-powered patient monitors require it for safety cer tification, and industrial-control gear often benefits from isolation to eliminate ground loops and to protect inputs from electrostatic events and sensors from power anomalies.
A simple way to implement isolated USB ports now comes from Analog Devices, which has offered its line of iCoupler MEMS-transformer isolators as a general-purpose alternative to optoisolators. The latest iCoupler, the ADuM4160 USB isolator, uses that technology to provide a complete USB 2.0 bidirectional isolator in a 16-lead SOIC for less than $5 in 1000-unit quantities.
The couplers provide 5-kV rms medical-grade isolation and upstream short-circuit protection, while passing USB 1.5-Mbit/s and 12-Mbit/s data. ADI says IEC 60601-1 medical safety approvals are pending. Also, the ADuM4160 operates off the 5-V USB supply or system-supplied 3.3-V power using an internal regulator. The isolator provides isolated control of the pull-up resistor, allowing the peripheral to control connection timing. Maximum idle current is 2 mA.
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