Altera/Enpirion DC-DCs aim to solve FPGA-power-supply challenges
Altera’s acquisition of Enpirion, designers of small-outline high-efficiency DC/DC converter modules, was one of the more unexpected corporate merger-and-acquisition deals – now, the company has announced the first results from the joint operation that are specifically aimed at Altera FPGAs. According to an Altera’s Mark Davidson, marketing director, power business unit, the company’s customers often face big challenges in providing correct power supplies to its FPGAs. There are multiple power rails, requiring precisely-controlled levels at low voltages and high currents: demanding transient response performance must be met; and in addition, correct sequencing at power-up and power-down is essential. Its customers, Davidson says, have had to apply, “engineering bandwidth to areas that are not key [to designing the actual functionalities of the FPGA]”
Accordingly, Altera has announced “Power-optimised FPGA reference designs” – both product and design process – to simplify the development of FPGA-based systems. Primarily for Cyclone V parts, there are four reference designs in this release. Davidson says its parts built in 14-nm silicon technology will require ±3% voltage rail stability and as with all complex FPGA designs, actual currents will be dependent on the configuration and operating parameters of the FPGA so point-of-load regulation will need to handle large current variations. Up to five power rails are needed for core, I/O, PLLs, peripherals and SERDES functions, with appropriate sequencing. Davidson emphasises the need for voltage stability, “[when] supplying a SERDES [function], noise on the rail appears as jitter on the data stream.” “All FPGAs need significant bulk capacitance,” he adds, before going on to detail how the solution reduces that need.
Enpirion brought expertise in three area, in its miniature-packaged-DC/DC designs; efficient high-frequency switching in CMOS; miniature magnetics; and the packaging itself. The four reference designs exploit those features, as “turnkey” power solutions that increase power efficiency by up to 35% (that is, reduce the losses by that percentage), reduce board area (used by the regulation) by up to 50%, and reduce overall bill-of-material (BOM) bulk capacitance costs by up to 50%. Multiple high-quality tantalum capacitors can amount to a significant cost in themselves. The designs are offered to customers as downloadable design packages and are demonstrated in hardware on development kits. A design package targeting Cyclone V SoCs is available for download, with additional design packages targeting 28-nm FPGAs available later in 2013. The designs include optimised board layouts and detailed schematics and have been verified by Altera to work corectly with its FPGAs and SoCs. Each design package contains the schematics for the FPGA’s power circuits, application notes, bill-of-materials list, power tree layout guidelines and Gerber files for individual power components.
The first power reference design available for download targets the Cyclone V SoC. Power reference designs targeting the Stratix V, Arria V and Cyclone V FPGAs will be available later this quarter. There are four corresponding 28 nm development kits. Among the features of the designs is that regualtion is good enough o enable provision to the SERDES function with a switching design; previously, usual practice has been to use a linear regulator in this function for noise reasons, with a corresponding efficiency penalty. “That design achieves the same, or lower, jitter, than the LDO version,” Davidson says. You can use fewer tanatalum capacitors, or an all-ceramic design may be feasible with attention to impedance issues; and the reference design will always work, irrespective of the FPGA configuration. Switching frequencies are in the range 2 to 9 MHz – the technology is capable of 18 MHz, but Davidson notes that this is not easy to use at present.
Going forward, Altera says that Enpirion’s primary goal will be to develop power solutions for its FPGAs – but the unit will continue to provide product to the wider market and will support applications that have similar needs for precisely regulated power.
The current Enpirion/Altera designs do not have a bus connection, such as PMBus, to control/report to a system power monitor but Davidson says that, “the way the FPGA business is going, that ius a high probability.” In these designs, some parameters are set by resistor value selection, and some by digital register values. Davidson concludes, “Discrete power [solutions] are always cheaper, but here Altera/Enpirion has the opportunity to save customer hassle while selling a premium product.”
Altera, www.altera.com/enpirion
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