Power Supplies Goes Digital

284 23-3095 Uen Rev A
POWER SUPPLIES GOES DIGITAL
October 2006
White Paper
Digital control inside an on-board power supply facilitates improved efficiency, reduced total cost and advanced system power management


POWER SUPPLIES GOES DIGITAL


Contents
1 Executive summary.................................................................................3
2 Digital Techniques in Power Conversion .............................................4
3 Digital Control and Management ...........................................................4 3.1 Power Supply Control................................................................................5 3.2 Power System Management .....................................................................8
4 PMBus.....................................................................................................12
5 Conclusion .............................................................................................14
6 Glossary..................................................................................................15
7 References..............................................................................................16

284 23-3095 Uen Rev A © Ericsson AB 2006 2 (16) POWER SUPPLIES GOES DIGITAL

1 Executive summary
Using digital control in power supplies is considerably more flexible than analog control in its ability to adapt to changes and digital control inside the power supply results in advantages to the system application such as improved efficiency, fewer external components and reduced overall cost.
The embedded digital control circuitry in the power supply can also be used for system power management purposes. Flexibility is the key and the power system designer may choose features and capabilities that are important to a specific application.
Digital power management can be used at several different stages of the power supply and power system life cycle; during manufacturing of the power supply, during optimization of the power system design, and with a host controller on the board, a lot of added functionality can be implemented. The PMBus is the most common interface protocol for digital power management of power supplies and the PMBus specification is freely distributed and available on a royalty-free basis.
The use of digital techniques results in capabilities and performance levels at both the power supply and system levels that is not possible with analog techniques and at the same time offering possibilities for significant overall system cost reductions.
284 23-3095 Uen Rev A © Ericsson AB 2006 3 (16) POWER SUPPLIES GOES DIGITAL

2 Digital Techniques in Power Conversion
The concept of "digital power" has been receiving significant attention and promotion in the past few years by both semiconductor suppliers and power supply manufacturers and there is a need for explaining the concepts of digital power, explore the advantages and tradeoffs of digital techniques compared to analog approaches, discuss some of the standardization directions and explore possible future directions that digital power may make possible.
Digital power is defined and implemented differently by various suppliers and there is not yet an appreciable field history of successful large-scale designs using digital approaches. The result is an atmosphere of uncertainty and perhaps confusion about digital power; is it cost effective, how does the performance compare to conventional analog approaches, what about reliability, does it affect the complexity of the design and development process, are developers with specialized skills needed, how "standardized" is it and will it affect second sourcing?
It is now the right time to take a more proactive stance in terms of defining the approach to enable the implementation of power supplies and systems using digital power. Most importantly, the above questions must be answered so that the end user, i.e. a system integrator or OEM, can move forward confidently with the appropriate uses of digital power.
So why is power conversion still mostly in the analog domain? The main reason is that efficiency is paramount in importance for most power system applications. ... [download for more]