Battery-powered portable product manufacturers are also facing increasing pressure to plug more functionality into products with limited form factors while still achieving longer battery life. For example, most portable media players (PMPs) have video and MP3 playback capabilities. Therefore, internal electronic circuits require a variety of low voltage output rails with different power levels. Clearly, the main reason for this result is that most large-scale digital integrated circuits operate at 1.2V or lower, while memory and I/O voltage requirements may be between 2.2 and 3.3V. In this way, the use of multiple single POL DC/DC converters for lithium-ion batteries is becoming less and less practical, so system designers are adopting a more integrated approach.
Synchronous buck converters offer significant improvements in battery operating time compared to traditional linear regulators because they increase conversion efficiency. These converters typically have a 95% conversion efficiency and require virtually no heat dissipation. However, this high efficiency comes at the cost of taking up more board space, because adding an inductor to each channel makes it extremely important to maintain a minimum overall solution footprint. By integrating multiple channels into a single synchronous buck solution, all of these channels can be operated with one input capacitor, keeping the solution footprint to a minimum.
Recently, the concept of “green environmental protection†has become popular and has been reported in the news media. As a result, most industrialized countries generally accept the idea of ​​saving energy. This is because as the population of these countries increases, their demand for energy increases, and they need to supply heating/cooling systems, lighting, and household appliances for new homes. Not only does it take a lot of money to build a new power generation facility, but the cost of supplying power to the user after the power is generated is also high. It has been observed that it is more economical to reduce the current consumption of most household appliances by 15% to 20% compared to the establishment of new power generation facilities.
Due to the high cost of establishing new power generation facilities, many countries have adopted so-called “green policies†to encourage manufacturers to include energy-saving technologies in their final products. Inspired by this policy, many power management product vendors have made great progress in improving the power conversion efficiency of products and reducing the power consumption of products in standby mode.
For power management integrated circuits for energy-efficient DC/DC converters, there must be two main features. First, it must have very high conversion efficiency over a wide range of load currents. Second, there must be low quiescent current in the standby and shutdown modes.
For many embedded systems, the need to continuously increase the current in the case of declining voltage continues to drive the development of power systems. Much of the progress made in this area can be traced back to the results of power conversion technology, especially for power integrated circuits and power semiconductors. In general, these components allow the switching frequency to be increased in a manner that minimizes the impact on power conversion efficiency, contributing to improved power performance. It is possible to increase the switching frequency and minimize the effect of efficiency by reducing the switching and on-state losses and allowing efficient removal of heat. However, the migration to lower output voltages puts more pressure on these factors, which in turn leads to great design challenges.
Multiphase operation is considered a general term for converting topologies in which two or more converters are used to process a single input, the converters are synchronized with one another, but operate at different locked phases. This approach reduces input ripple current, output ripple voltage, and total RFI characteristics while allowing a single large current output or multiple lower current outputs with the output voltage fully stabilized. In terms of the ability to increase the output current with a single device, it also allows the use of smaller external components because multiple smaller MOSFETs can be fabricated "on the chip" very easily.
Although buck converter applications are more common, multiphase topologies can be configured for buck, boost, or even forward. Today, conversion efficiency of up to 95% from a 12V input to a 1.xV output is common. In addition, efficient operation is possible over a range of load currents across multiple orders of magnitude by using a pulse skip, pulse width modulation (PWM) technique. This has the added benefit of providing low quiescent current when supplying small currents to the load. Normally, the quiescent current is in the range of several tens of μA.
The solution for embedded systems is not much different from the solution for battery-powered handheld devices, with the possible exception that many portable applications have strict limits on component height. This can be a problem for power converters because inductors and filter capacitors are usually the highest components. However, the multiphase architecture is well suited for this type of application, with component heights even reduced to just 1.5mm.
Many single-chip multiphase converters from different analog IC vendors offer smaller size and lower height than comparable single-phase converters, providing more than 10W with higher efficiency and lower output ripple. Output Power.
For example, consider monolithic, synchronous, high switching frequencies (up to 2MHz per phase), four-phase power integrated circuit architecture. An example of such a product is the LTC3425, as shown in Figure 1. It allows the use of multiple small, low-cost inductors instead of a single, bulky, bulky inductor, and requires much less output filter capacitance than comparable single-phase circuits because of the effective output pattern The wave frequency is up to 8MHz. In addition, all of the required power MOSFETs are on-chip. This is ideal for boards and portable devices that require flat components and space constraints.
In addition, designing a converter with a multiphase method is no different than designing a conventional single-phase converter. All power switches are internal, so the four-phase operation is transparent. All four-phase current limit and switching frequency can be easily programmed with a single resistor, just as in a single-phase design. Similarly, output voltage settings and loop compensation are no different from other familiar DC/DC converter designs.
The synchronous four-phase architecture of this type of POL converter achieves high efficiency over a wide load range while allowing the use of flat components. Finally, since the output ripple current is reduced by a 4:1 ratio, very low output voltage ripple can be achieved with small and lower cost ceramic capacitors.
Designers of POL DC/DC converters in almost any system face many challenges due to various constraints such as limited space and cooling in the chassis, as well as the need for proper power tracking to improve system reliability. Despite the need to overcome a number of constraints, designers have a way to go, and many analog IC manufacturers have recently introduced a number of regulators that provide a simple, compact, efficient, and feature-rich solution.
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