How PMBus offers open-standard digital power management

Most modern dc-dc converters are still configured and controlled via analog signals derived from simple passive components. Even sophisticated high functionality converters, with state-of-the-art power conversion topologies, are likely to use external trim resistors and capacitors for defining values such as startup time, setpoint value and switching frequency. And of course, none of these parameters can easily be changed on the fly, making it virtually impossible to implement adaptive – let alone predictive – power management schemes.

With the exception of a few specialist converters for microprocessors (which offer limited digital programmability in the form of VID codes for output voltage control), most brick, intermediate bus and point-of-load (POL) converters on the market still operate in the analog control domain. The most urgent need is for digitally controlled non-isolated POL converters, because these are used extensively to provide the final voltages for devices on a board. However, the requirement also already embraces isolated converters, and designers will doubtless shortly be adding other digitally programmable power sources to their wish lists.

PMBus demonstrator kit, which includes a USB-driven board with eight digitally programmable POL converters and a PC-based graphical user interface

The reason for this seemingly odd scenario is simple: until now, there has been no industry-wide consensus on digital power management. A number of power supply manufacturers have launched digitally programmable POL converters which go some way towards addressing the issue, but these are based on proprietary architectures and silicon.