A blade server is essentially a single circuit board populated with components such as processors, memory, and network connections that are usually found on multiple boards. The explosive growth of mobile applications and the increasing use of Software as a Service (SaaS) has made protecting the blade servers that store data “in the cloud” and keeping them operating efficiently more important than ever. Making that happen depends in part on preventing over-current damage that can shorten their lives and disrupt datacenter operations.

One factor complicating ensuring blade protection is the trend toward concentrating ever-higher levels of computing power on each blade. Once, blades typically ran at maximum power levels of 200–400W; today, however, blade power levels of 600–800W, sometimes even 1000W, are increasingly common. The trend toward increasing power has developed at the same time as a trend has emerged toward decreasing blade operating voltages in order to reduce DC-DC conversion costs and power efficiency losses within the data center power distribution scheme. In some popular designs, a typical low side voltage is 12VDC, which can drive input current levels to greater than 80A per blade. For the blade’s circuit designers, the challenge is to ensure over-current fault protection in a cost-effective, reliable, safe and feasible way to prevent costly hardware damage and service outages.

Figure 1. A blade server chassis is designed to hold multiple blade servers and provides services such as power cooling, networking, various interconnects, and management.
Because blades are intended to be hot-swappable (i.e., to allow maintenance personnel to remove them from the chassis and plug in new ones while the main power is still on), they are designed with a hot-swap controller IC. This IC provides the primary fault protection mechanism by first sensing over-current and other fault conditions, then signaling a MOSFET to shut down power to the board. The objective is to prevent adjacent blades within a chassis from going down due to undervoltage lock-out (a short circuit can cause the backplane power rail voltage to go down due to droop) and also prevent damage to the faulted blade and backplane. Critical components within this system are the backplane traces, backplane connectors, and power connector on the board. Backplane damage can be particularly problematic because it could lead to the loss of an entire chassis within the data center.

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