FireWire Frying Elucidated

About five months ago I privately implored James to publicly document the over-voltage protection they had quietly rolled into their Super Drive Dock, a feature which soon spread through their product line. While I'm disappointed they didn't release a dedicated press release on the topic, it is mentioned in this white paper. However James, being more of a gearhead than a PR maven, hid this nugget under section 5.2.2, Voltage Transient Suppression Circuitry On Bus Powered Devices:

WiebeTech has implemented a proprietary technique which prevents transients at power on time from being transmitted to the host computer via the Data lines. This resolves issues related to use of bus powered devices. This technique has been used with excellent results in WiebeTech's bus powered FireWire DriveDock devices, which are capable of bus powering 3.5 inch IDE hard drives.

Also hidden away in this white paper, under section 5.2.3, is a recommendation I've been making as well:

WiebeTech recommends the use of power switches in bus powered FireWire devices. This prevents the PHY within the FireWire device from transmitting voltage transients through the FireWire cable to the PHY on the motherboard of the host computer. Simply put, the FireWire device is not powered up until all connections have been made and voltages have had a chance to stabilize. This technique is used on WiebeTech's portable drives, including the MicroGB+; MicroGB+Combo; and 3.5 inch bus powered UltraGB.

Bottom line: ground yourself, plug in the cable, and then power-on the FireWire device.

Thursday, April 17, 2003
10:13 AM