The challenges facing system engineers is driving innovation in the delivery and distribution of board level power.
Equipment and device manufacturers are coming under increasing pressure to prove and maintain their 'green' credentials and as a result their suppliers – semiconductor vendors – must embrace technologies that offer greater energy efficiency. The issue remains that products need power and their consumption of power incurs inefficiencies in how that power is delivered and distributed. The challenge facing the electronics industry today is therefore twofold; deliver more processing power for less system power, and deliver that system power with greater efficiency. The former problem – which is, essentially, 'do more with less' – isn't new; it is the underlying requirement that has driven developments in the semiconductor industry since its inception. Moore's Law may be the public face of this requirement, but commercial viability sustains it. Without continued improvements, the semiconductor industry would stall and, perhaps more importantly, the rate of progress in general would decline. The latter problem has also been a long standing objective for manufacturers, but for different reasons. From a technical point of view, meeting the needs for system power is a challenge where the only constant is change. Until the semiconductor industry ran in to power density issues, the prevailing trend was for more power in smaller footprints. Now, with integrated device manufacturers focusing more on lowering their system power requirements, the objective is to deliver the right amount of power in the right place with as much efficiency as possible. The history of system power has demonstrated considerable innovation in how power is distributed. Centralised conversion was a good starting point when the requirements were for a single dc voltage, but this very quickly gave way to the need for multiple voltages, bussed throughout a system. This has been achieved using a distributed topology, where localised conversion is used to generate low voltages at the point of load. The challenge now facing the power supply industry is to continue to innovate, developing new solutions to the new problems in power distribution. The fourth dimension One such problem is the need to sequence power at start up. Many power supply manufacturers are now members of the Power Management Bus Implementation Forum (PMBus IF), part of the System Management Interface Forum. This open standard power management protocol provides a solution to controlling PMBus-compliant power supply components, in terms of their operational parameters at start-up. For instance, a central controller can communicate with an individually addressed point of load converter to alter the time at which it turns on following a system restart. This functionality has become essential in today's embedded systems due to the interdependency between functional units within a system. It also imposes overheads on the power supply component, in that it must be capable of communicating via the PMBus' physical interface, interpreting commands and in most cases storing operational parameters in a local non volatile memory. Earlier this year NXP partnered with Transim Technology, an online design tools provider, to create a web portal that engineers can use to configure NXP's PIP8000 PMBus controller. The tool is able to communicate with the controller via a USB interface, automatically locating all PMBus compliant devices connected to the controller, allowing voltage and current settings to be adjusted, control fan speeds and monitor the thermal behaviour of the power management system. This illustrates graphically the complexity involved with power management in today's embedded systems, particularly in relation to the fourth dimension – time. It is no longer acceptable for an embedded system to operate at full power all of the time, power constraints dictate that in order to extend battery lifetime in portable systems particularly, they must be more aware of their operational requirements and be capable of shutting down areas of the system that aren't being used. This has given rise to a new direction in power management, which brings it closer than ever to the functionality of a system. A recent example from Texas Instruments demonstrates the concept, with the introduction of a family of low dropout (LDO) linear regulators which feature an automatic low power mode, combined with a low quiescent current of less than 8µA. TI claims this is as much as 70% lower quiescent current than existing solutions, which could help extend battery life in a range of portable devices. The TPS727xx LDOs enter low power mode automatically by detecting the load current, which removes the need for an additional mode pin and the subsequent control software to manage it. TI also recently introduced a family of integrated power management units which support three system voltages – one for the processor, one for memory and one for I/O. The TPS65070 and TPS65073 also feature two general purpose 200mA LDOs, white LED backlighting to support LCDs of up to 5in and a touch screen interface, as well as a 1.5A linear battery charger. Increasingly, the challenge of delivering system power is impacting other areas of embedded system design, to the extent that suppliers previously uninvolved with power management are making it part of their portfolio. The reasoning behind this seems to be strategic; in order to deliver a high quality product, the supplier must now also take control of the power management aspect of a design. A case in point is Wolfson Microelectronics, a company more associated with audio solutions for portable equipment, but one that is becoming more involved with power management as a result. Earlier this year Wolfson introduced a family of power management ICs (PMICs) which Jess Brown, Wolfson's power management product line manager, described as 'the only PMIC solution designers will ever need'. The family features Wolfson's 'BuckWise' technology, described as having the best in class transient performance, eliminating the need for large external components. The latest PMIC device from Wolfson, the WM8320, targets applications using ARM based processors, particularly netbooks, mobile internet devices, smartphones, handsets and digital photo frames. It offers four dc/dc synchronous regulators, two of which incorporate its BuckWise technology, as well as ten LDO regulators. There is consensus within the industry that power management is now more critical than it has ever been. Future innovations are likely to include more intelligence, as it becomes necessary to apply greater discretion in the distribution of power. In conjunction with that, it will be necessary for the power management function to integrate more closely with overall system functionality in order to achieve intelligent control. Many power supply companies have adopted the distributed point of load approach to dc/dc conversion, primarily because the power requirements demand it; supplying processors operating at sub 1V with high current requirements needs localised conversion in order to overcome the inefficiency of bussing high power around small systems. The challenge is equally appropriate for mains powered devices, where power density dictates a differentiated approach. This is evident from Vicor's factorised power architecture; the next phase in distributed power. It uses a combination of three devices which work together to meet differing power requirements most efficiently, extending beyond the original 'brick' format to encompass single chip integrated solutions. The issue of power density is unlikely to disappear in the face of power saving developments at the chip level. While individual ICs may strive to consume less power and the overall system power budget is pushed downwards, the physical dimensions of end devices is also shrinking which will contrive to create altogether different challenges for the power industry.