Electronic Design

Power Supply Eyes Next Generation Of Blades

Five of these 850-W supplies will fit in a 1U rack enclosure, while I2C monitors volts and amps as well as controls VOUT and fan speed.

Five of these 850-W supplies will fit in a 1U rack enclosure, while I2C monitors volts and amps as well as controls VOUT and fan speed.

Blade servers—hot-swappable, independent server cards that fit in a rackmount enclosure like books in a bookshelf—hit the big time in 2002 after a flurry of startups began introducing the concept in 1999. Each blade server, with its own processors, memory, storage, and network controllers, slides into a bay in the chassis and plugs into a mid- or backplane. They share power, fans, floppy drives, switches, and ports with other blade servers. Blades are a distinct improvement over the older pizza-box approach, with individual supplies and fans, not to mention tortuous bundles of cables.

The first couple of blade-server generations ran their blades on 12 V dc, using off-the-shelf power supplies. To meet the needs of new generations, Power-One introduced the first member of a new, hot-swappable, power-factor-corrected, power-supply family for blade servers and other high-density networking and storage systems. Each FNP850-12 provides 850 W in a 1U high by 2U wide by 11-in. deep form factor. That's more than 15 W/in.3, compared to about 10 W/in.3 for its closest competitor. In practical terms, that means a 1U rack enclosure could hold five power supplies, providing 3.4 kW. That's enough for four blade chassis, with one supply left over for redundancy.

Blade servers themselves provide an I2C bus in the rack for control and monitoring of individual blades. The FNP850-12 takes advantage of that bus, along with an internal microprocessor, to provide the system monitor with basic information (power supply seated, fault monitor status, fan status, input and output voltages, output current, and temperature), as well as actual output voltage and current (to 0.1 V and 0.1-A resolution) and time in service for each supply.

Thus, it's possible to log these vital characteristics and spot potential problems well before they become failures. Supplies can also be interrogated for maintenance record-keeping data, including part number and revision level, output rating, serial number, date code, and manufacturing location.

Beyond that, network system operators can use the I2C bus to control each supply's output voltage and fan speed. Although each FNP850-12 is nominally rated for 12-V output, it can actually be remotely adjusted between 12 and 7 V.

Voltage control will be particularly significant in future blade-server generations. While today's blades typically run at 12 V, this isn't necessarily the optimum bus voltage for distribution to point-of-load (POL) regulators for the blade's CPU and custom chips, which operate at 2.5 V and below. The greater the step-down ratio of a non-isolated dc-dc POL buck converter, the more its efficiency suffers. Beyond a 10:1 ratio, POL inefficiency generates too much heat.

Arguably, then, something lower than 12 V should be bused to the blades. (On the other hand, 7 V is about as low as you can go before I2R transmission losses become significant.) I2C voltage control makes it possible to keep just one type of supply in backup inventory and program each unit in situ when needed.

The ability to control fan speed via I2C has two advantages. First, slowing the fan during periods when the supply isn't converting at maximum power extends fan life. And fans, being mechanical, are the most likely failure point in the supply. The other reason will be obvious to anyone who has spent much time in an equipment room. Any individual fan may seem quiet by itself. However, many fans working at the same time produce an appreciable level of background noise. Management of that din is a considerable boon for the technicians who have to work in that environment.

The FNP850-12, which operates from 85 to 264 V ac, measures 1.6 by 3.3 by 11 in. In addition to its main power output, an auxiliary or standby 12-V, 0.5-A output is also available for system startup and/or I2C operation. This output continues to work as long as the input ac is provided, enabling the system to continue to monitor and control the unit even in a power-supply Inhibit situation.

In addition to the status information on the I2C bus, logic signal and front-panel LEDs also indicate power-supply conditions. Overcurrent and overvoltage protection are standard features. An output blind-mate connector, built-in ORing diodes, and droop-current-sharing circuitry simplify hot-swapping in N+1 redundant applications.

Agency approvals include UL60950, CSA 6950 (UL/cUL), and EN60950 (TUV). It's CE-marked to the Low Voltage Directive (LVD). In addition, the unit meets the various EN61000-4 EMC susceptibility requirements, including ESD
(-2), Radiated (-3), Burst (-4), Surge (-5), Conducted (-6), and Input interruptions (-11). Class B is met for both radiated and conducted electromagnetic interference.

Pricing for the FNP850-12 is $500 each in quantities of 250 units.


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