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Digital control in power supply applications

In recent years, the interest in digital control for switching converters has grown considerably. The digital control approach potentially offers several advantages compared to the analog counterpart, such as the immunity to component variation, the ability to perform sophisticated control algorithm, and self-calibrations, faster IC design using HDL synthesis and controller adaptation. In spite of these potential advantages, one of the limiting factors when using IC digital controller in high-frequency switched-mode power supplies (SMPS) is the achievement of dynamic performance comparable to those of analog controllers, especially in the presence of significant control delays and quantization effect. Thus, one of the major challenges in digital control for SMPS is the development of simple digital or mixed-signal control architectures with little additional silicon area required which ensures dynamic performances comparable to analog controllers. Such a controller usually requires high-resolution analog-to-digital conversion and digital-pulse-width modulation (DPWM). The IC implementation of such a control is usually complex. It is also hampered by the undesirable quantization effect and limit cycle oscillation. Researchers at CPES have developed a novel DPWM method based on constant-on time control or constant-off time control that could achieve a resolution approximately 10 times greater than conventional DPWM methods. This is particularly beneficial for microprocessors and related applications. The design challenge of DPWM block could also be greatly reduced. We are currently discussing this concept with industry partners and a potential user -- Primarion -- for possible implementation in their commercial digital control IC.
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