The Evolution of the Buck-Boost DC/DC Regulator
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The concept of sustainable design started, not as a way of conserving the environment, but to prolong battery life in portable consumer goods such as cell phones, laptops and PDAs. Many of the concepts developed for these devices have now passed into mainstream applications, including advanced power management and LED backlighting.
There are many reasons that these concepts have moved into the design of mainstream products, but perhaps the most important one is the onset of environmental legislation in an increasingly global marketplace. Adding to the complexity is the current trend to design one product for the global market, which means designers must be cognizant of directives such as the European Union’s RoHS, New Batteries, EuP and REACH.
The power chain is the logical place to begin this optimization process, as powering the circuit’s boards and components incorrectly will exacerbate any inefficiency inherent in the design, and conversely, a good power chain design will ensure that a good design works as efficiently as possible.
Whether a device is powered from the mains or a battery, voltage has to be converted at least once, and usually more often, to be able to supply circuits with the correct input voltages. Designing the power chain to be as efficient as possible will provide other benefits apart from using less energy.
System Level Design and Module Efficiency
The first step in producing an efficient power chain design is to get a top level view of the entire system. While the standalone efficiency of the power supply, conversion or regulation elements of a product are very important, it is also critical to minimize losses and maximize the efficiency of the overall product. Different system architectures can have a significant bearing on overall energy efficiency, so it is important to make the right choices early in the design cycle.
This chart shows the reduction of energy consumption in digital processors
by up to 64% using National’s PowerWise Adaptive Voltage Scaling (AVS) technology
Manufacturers offer ranges of modules designed to complement each other, and they can provide a quick and easy way to implement an efficient power supply design. To implement a modular solution, the designer must be prepared to compromise a little on cost, board space and flexibility. But modules can provide an especially good solution for low to medium production quantities. Companies such as XP Power, Lambda and Murata Power Solutions to name a few, are using the latest semiconductor technologies, plus a host of other innovative features and processes in their latest power modules.
Examples of these technologies include: multi-layer heavy copper PCBs, synchronous rectifier topologies and planar magnetics. These all lead to increased efficiency and higher power density, and they support feature-laden products housed in small footprint packages.
There is a strong link between small form factor design and higher efficiencies. However, without careful design, modules with high component densities can be more prone to thermal issues. This potential problem needs to be managed carefully so that the good work done improving efficiency and power consumption at module level is not undone by a necessity to consider additional thermal management.
For higher production quantities, a custom power chain design using discrete components can offer the maximum efficiency, lowest cost and smallest board real estate. Some of the biggest developers of power chain components such as National Semiconductor, Texas Instruments, Freescale, Maxim, Linear Technologies, International Rectifier and Analog Devices continually vie to have the lowest power and most efficient products for a range of end markets. There have been strong technical advances in the power electronics sector in recent years that have helped yield specification improvements including higher efficiency.
Advances have also been made in miniaturization, integration and mixing technologies. Many, if not all of the companies mentioned above have integrated both analog and digital logic on the same die. National Semiconductor’s Adaptive Voltage Scaling and Freescale’s SMARTMOS technologies are two examples of this methodology. The mixed technology adds intelligence to the component and allows extra features to be incorporated on the same die.
XP Power’s JCA range of miniature, board-mounted low power DC/DC converters measures just 10 3 0.80 3 0.40, allowing designers to reduce the size of new developments or add in more features, while maintaining the industry standard pin-out. The JCA range has 2W, 3W, 4W and 6W models, each offering a choice of four input voltages of 5V, 12V, 24V and 48V DC. For each input voltage, single output models offer +3.3V, +5V, +12V or +15V DC outputs or the dual output versions provide ±5, ±12 or ±15V DC. Outputs are fully regulated, varying no more than ±0.3 percent over all input conditions, and less than ±1.0 percent across all load conditions.
The example above is for a general solution, but DC/DC converters can often offer more efficiency when targeted at a specific end market, because of their ability to offer higher integration and focused features. For example, Analog Devices’ ADP1829 switching regulator offers a solution for the industrial, telecoms and networking industries. The ADP1829 is a dual, interleaved, synchronous PWM buck controller, which provides high-efficiency DC/DC power conversion and generates two independent output rails, as low as 0.6V, from an input of 3V to 20V. The two channels operate 180° out of phase, reducing stress on the input capacitor and allowing smaller, low cost components.
Designed specifically for the automotive market, Linear Technology’s LT3680, is a 3.5A, 36V step-down switching regulator with Burst Mode operation to keep quiescent current under 75 µA. The LT3680 operates within a VIN range of 3.6V to 36V, making it appropriate for the load dump and cold-crank conditions within automotive applications.
As more and more devices are powered by batteries, special power chain solutions are required to ensure a longer usable lifetime. Texas Instruments’ 120x devices provide a power supply solution for products powered by a single-cell, two-cell, or three-cell alkaline, NiCd or NiMH, or one- cell Li-Ion or Li-polymer battery. It is also used in fuel cell or solar cell powered devices where the capability of handling low input voltages is essential. Possible output currents are dependent on the input to output voltage ratio.
Designing a product to be as efficient as possible will soon become the norm, rather than the exception. The best place to begin is the power chain, as a bad power chain solution will negate any savings made by an efficient design, and a good solution will make the best of even an averagely designed circuit. The switchover to a high efficiency power chain may not be as difficult, and will definitely not be as expensive as may be expected. In fact, with the savings on bills of material to requiring less thermal management products, the cost differential may even work in the designer’s favor.