Power Management Design Guide for AlteraÂ® FPGAs and CPLDs ...

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How to use this guide Introduction National Semiconductor — working in close collaboration with Altera — has developed this comprehensive design guide for design engineers who are utilizing Altera’s latest FPGAs and CPLDs, to help them easily select and implement the best power management solutions for their designs. This design guide presents National’s power supply solutions down to specific part numbers with multiple reference designs illustrating how these power management ICs are used in actual applications. This guide recommends the optimal National products for select Altera devices based on the device’s specified power consumption in specific applications. The reference designs were created by National and verified by Altera, combining the experience and knowledge of both companies to ensure that the highest-performing, most-reliable power solutions are being offered for the latest, most-powerful Altera devices. Additional information is available on National’s website, including bills of material and test data for the reference designs, along with detailed information on other National solutions for Altera FPGAs, from LVDS transceivers to high-speed ADC and integrated Bluetooth ® wireless modules. For more information, visit: www.national.com/see/alterafpga How to use this guide This design guide is organized into two major sections: selection guide tables and reference design schematics. The use of this guide is a simple two-step process. 1. In the selection guide, find the Altera FPGA or CPLD to be used in the design. Review the power consumption data for the device and select a National regulator for powering V CCINT and V CCIO . 2. Go to the Reference Design section to find complete Altera FPGA-based power supplies using the recommended National product ID. This design guide also provides information on additional National ICs for FPGAs, from core power management (including DDR and DDR-II memory regulators and active termination), and voltage supervisors to stand-alone LVDS interface and buffers, and other related analog and mixedsignal technologies, including high-speed analog-to-digital converters (ADCs) and high-speed operational amplifiers. Step 1: Review the power requirements for your specific device Step 2: Choose the best National solution based on your specific operating conditions EP2S15 V CCINT (V core) 1.20V I CCINT max (I core) 2A V CCIO options (V I/O) 3.3, 2.5, 1.8, 1.5V I CCIO max (I I/O) 10A (all 8 banks) V CCINT V CCINT = 1.2V V IN = 12V I CCINT < 1000 mA (LDO) Not applicable 1 I CCINT < 1000 mA (SW) LM2734 I CCINT < 3A LM2673-Adj I CCINT < 5A LM2679-Adj 2 or LM2743 3 I CCINT < 7A LM2743 or 1 / 2 LM2647 4 I CCINT < 9A LM2743 or 1 / 2 LM2647 4 I CCINT < 12A LM2743 or 1 / 2 LM2647 4 I CCINT < 16A LM2743 or 1 / 2 LM2647 4 2
Selecting the best power architecture What is the best power architecture to use? Linear regulators Linear regulators are some of the simplest, easiest-to-use regulators available. To operate, these devices typically need only two external components — an input and an output capacitor. They also feature very clean low-noise outputs. The main disadvantage of the linear regulator architecture is power dissipation. When using a linear regulator, the power that is no longer needed at the output is simply dissipated as heat. When this dissipated power is less than 1W or 2W (max.), the solution can be surface-mounted and implemented without a heatsink if using an adequate package for the regulator. However, for dissipated power P D > 2W, a linear regulator architecture is usually not recommended because temperature rise, system efficiency, and overall solution space are better addressed using a different topology. For linear regulators, dissipated power can be estimated as (V IN – V OUT ) * I OUT . For a 5.0V to 3.3V conversion at 500 mA, P D is roughly (5.0 – 3.3) * 0.5 = 0.85W. Typically, linear regulators do not offer an option to adjust the turn-on rate (softstart) and thus may require additional external circuitry to implement this functionality. Switching regulators Switching regulators offer a consistent efficiency (typically 85% to 95%) under most operating conditions (V IN , V OUT , I OUT ). Unlike their linear counterparts, these devices offer high efficiency, low heat dissipation, and the ability to stepup or step-down a voltage. Generally, a switching regulator uses an inductor in addition to input/output capacitors. Other external components might also be needed based on the specific topology used and functionality required. Buck regulators Buck regulators are the simplest step-down switching regulators to use. They offer good efficiency and low external component count (diode, inductor, and input/ output capacitors, at a minimum). Most National buck regulators (particularly those from the SIMPLE SWITCHER ® family) offer free online design tools, as well as electrical and thermal simulation. Synchronous buck converters Synchronous-rectification buck converters are a variation of standard buck regulators. The main difference is that the diode placed between the switch node and ground (catch diode) is replaced with a second active switch (MOSFET or bipolar transistor), reducing the power loss at this element. This is an important enhancement when the output current is high and when the diode dissipates a significant amount of power as heat. For output currents >5A, a synchronous buck converter is always recommended. As with standard buck regulators, synchronous buck converters are offered with monolithic (integrated) pass transistors or can use external ones. The advantage of using an external pass device (MOSFET or Bipolar) is more evident for output currents >3A, when there is a need to get very low RDS ON pass devices, distribute heat dissipation in more than one element around the board, and attain a cost-effective solution. Figure 1 shows a summary and a comparison of the three main power architecture solutions discussed above that are suitable for FPGA power. Buck Synchronous buck Linear regulator Function: Step-down (V OUT < V IN ) When to use: Typically when V IN is 3x to 5x V OUT and I OUT is > 0.5A and < 5A Characteristics: Easy to design and good efficiency for the above-mentioned typical V IN /V OUT /I OUT conditions Devices to use: All buck integrated regulators and controllers Function: Step-down (V OUT < V IN ) When to use: When high efficiency is required with high-output current (> 5A) or low duty cycles (V IN > 5 x V OUT and/or I OUT < 0.5A) Characteristics: A second switch replaces the diode in the basic buck topology, reducing losses in the conditions mentioned above Devices to use: Any “synchronous rectification” buck integrated regulator or controller Figure 1. Step-down configurations Function: Step-down (V OUT < V IN ) When to use: Typically when I OUT < 1A, ultra low-dropout, and low-noise applications) Characteristics: Excellent option where fixed output, low current, and low voltage drops are required. Easy to implement Devices to use: Any low-dropout, linear regulator Comments: Great for micropower applications 3
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Page 25 and 26: Select voltage supervisors/power-on
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Power Management Design Guide for AlteraÂ® FPGAs and CPLDs ...

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