Technical Article

Get to Market Faster with Digital Power

March 17, 2015 by Ramesh Balasubramaniam

This article presents the advantages of transitioning to digital power regulators for faster and easier design process and reduced design cycle.

In our competitive world, being first to market gives your product that slim edge that can mean the difference between success and failure. Everyone knows that companies generate profits by getting their products to the market faster. It’s why we have simulation and emulation tools, logic synthesizers, software debuggers and the like. Every facet of equipment design has been digitized and optimized, except for power, until now.

Traditional analog power supply design and verification techniques continue to be laborious and painstakingly slow as you try to work around the limitations of the power supply vendor’s chosen feature set. But advanced digital power (digital power 2.0) supply design changes all that, now you are in control of the power, not the other way around – it’s like TiVo for your power supply! Here’s why:

Figure 1 shows a typical sequence of events required to design, optimize, characterize and validate a power supply in a system.


Typical design sequence

Figure 1: Typical design sequence


In an analog design environment, step 1 (Design Schematic & Layout) requires careful forethought and planning. Figure 2 compares the circuitry that has to be designed in advance to characterize a power supply in an analog system versus a digital system. It’s not enough to just design for the right power delivery and performance, you must also prepare for measurement capability, voltage margining, slew rate adjustments etc. in short, you must prepare for the unforeseen! The analog way is incredibly time-consuming, requires more board space, is prone to mistakes and cannot deliver all of the characterization options and measurements – it’s highly custom design. Digital power regulators have all these knobs built in so that you only spend your effort designing the power delivery and performance – International Rectifier’s approach is even faster as you only need to choose from a few preset schematics. What can easily take one week in Analog power supply design can be shortened to as little as one day with digital power. Furthermore, all this functionality is already verified by the digital power supply manufacturer so you are not wasting time verifying the characterization circuitry.


Design of Characterization circuitry

Figure 2: Design of Characterization circuitry


Once the board has been designed and built, the process moves into step 2 (debug VR). One of the greatest frustrations in debugging an analog power supply is trying to determine why it shut down - is it over current, is it over voltage, is it over temperature, or something else? Rarely do analog regulators provide fault diagnostics beyond the Power Good signal, so hours must be spent trying to re-capture the problem whilst using an oscilloscope to monitor several signals in an attempt to determine the shut-down mechanism. Digital power supplies, on the other hand, can immediately stream out the fault mechanism. Furthermore, the fault thresholds can be adjusted based on system characterization. Figure 3 shows the status tab of an International Rectifier PMBus™ enabled regulator indicating the wide variety of fault diagnostics available from a digital power supply.


International Rectifier Fault Status Reporting

Figure 3: International Rectifier Fault Status Reporting


Once the power supply is up and running, steps 3 and 4 are to optimize and characterize. Optimization the analog way requires soldering and de-soldering components to change parametric values such as switching frequency, output voltage, compensation bandwidth etc., once again, a laborious, time-consuming task. On the other hand, Graphical User Interfaces (GUI) for digital power supplies typically allow the user to change these parameters at the press of a button. Quite often, the parameters can even be changed on the fly without having to shut down the board. Figure 4 shows how easy it is to change the switching frequency of an International Rectifier PMBus voltage regulator.

Characterizing the power supply becomes quick and easy with digital voltage regulators as they can stream out telemetry information such as voltage, current, temperature, efficiency, power and dissipation. In addition, International Rectifier PMBus regulators also store and provide peak current, peak voltage and peak temperature readings to truly understand the environment of the power supply.

For analog power supply regulators, most often an FPGA or CPLD is added into the system to control the sequencing and assist with these validation tasks. That’s an added expense, both in terms of system cost and extra design time. With digital power regulators, sequencing is simply controlled by setting the on/off delays and rise and fall times to achieve the desired start-up and shut-down sequences. Margining the power supply rails is childishly easy with digital power components and allows all sorts of combinations to be tested e.g. all rails margin up/down together by the same or different amounts or margin some rails up whilst others are being margined down at the same time. “But margining is easy too in an analog power supply system”, I hear you cry. Looking at Figure 2a, it theoretically only takes one resistor extra into the feedback node to create a marginable supply. However, in practice, you have to be extremely careful to set the margin slew rate and the margin amount very precisely to avoid tripping the regulator’s over/under-voltage detection circuits and power good flag. All this is automatically taken care of in a digital voltage regulator.

For an analog power supply, we have reached the end of the process. But for the digital power supply there is an added bonus not even possible with analog regulators. Digital power supplies allow the capability for field programmability. As long as a communication link can be established with the system in the field, a digital power supply can be monitored and updated from anywhere in the world. One has only to think about wireless base-stations in remote areas to realize the potential for huge time and cost savings that this facility brings.


International Rectifier Switching Frequency control

Figure 4: International Rectifier Switching Frequency control


The last parts of the process (Steps 5 and 6) no longer look at a voltage regulator in isolation but instead focus on the interaction of all the voltage regulators in the system as a whole. After all, it’s the system performance that the end-user cares about. What’s important here is to ensure the right sequencing between the power supply rails, margin the rails randomly against each other to test for sensitivities and review that the entire system’s power dissipation is to budget.


Design Cycle Reduction with Digital Power

Figure 5: Design Cycle Reduction with Digital Power


In conclusion, it is plain to see that all steps in the design process are significantly speeded up by transitioning to digital power regulators. As Figure 5 shows a 6x reduction in the design cycle is easily achievable by transitioning to advanced digital power 2.0 and that means that you can get to market faster!


About the Author

Ramesh Balasubramaniam works as the Marketing Director at International Rectifier, an Infineon Technologies company since April 2011 where he is skilled in the field of semiconductors, power management, and analog circuit design. He holds a Master's Degree in Microelectronics as well as Master's Degree in Electronics earned at the University of Southampton and University of Glasgow respectively.