(Editor's Note: this is an extended commentary which provides personal perspectives and discusses some strategies for optimizing the design of power systems in handheld devices, as well as needed improvements.)

Efficiency and solution size are two terms that are constantly associated with power-management solutions for battery-powered handheld devices. However, in my experience, they are very rarely placed into the context of the handheld designer or the end customer.

How many times have we heard or said "this power solution is 95% efficient"? I admit that I have used that as an opening line during many customer visits. However, how often to we think about what "95% efficiency" means to the system designer? Let us start by looking at the significance of efficient power regulation.

Prioritizing Power Regulation
Ideally, handheld designers would like to use the most efficient solution for every application in their designs. However, more efficient power regulation usually implies larger solution sizes, longer bill of materials, and higher costs. Conversely, the trends driving the handheld industry are cost and smaller form factors, and therefore the handheld designer has to prioritize.

It is important to address the most power-hungry sections in a handheld unit first. For example, it would be great to use a switcher to power a 1.8 V flash memory which consumes a maximum power of about 20 mW. However, 90% efficiency from a switcher versus 50% efficiency from a LDO translates into negligible improvement in battery life here.

In contrast, an inefficient solution for a display backlighting solution which can consume as much as 2 W would definitely hurt the run time of the device. The first step is to recognize the best sections to target for efficient power regulation. As a power-solution supplier, I would really be helping my customers by addressing the issues that worry them the most. But providing power regulation is only the first step. The challenge is to make the energy in the battery last as long as possible.

Minimizing energy consumption
Energy is defined as the product of power and time. Therefore, it's important that the sections used for the longest duration are running on minimal power. For example, a baseband processor in a cell phone is never turned off but spends more than 90% of its time in standby operation. Choose a power IC which has extremely low leakage current (tens of microamperes) to maximize the run time of a cell phone.

Another tactic for energy conservation is to minimize the number of power conversions in a system, or minimize the number of power ICs between the battery and the end application. A 90%-efficient regulator is still wasting 10% of the energy applied to it. If there are two such power ICs in the power train, the regulation is actually only 81% efficient (0.9 x 0.9), not even taking into account the additional power dissipation in the passive components, such as inductors.

This is where innovation is critical. Often, designers focus on their particular application but neglect the power design. The power-application experts can improve the situation by using the same regulators, but in a configuration which optimizes energy efficiency in the system. For example, sometimes a voltage is stepped-up and then stepped-down, using a boost and buck regulator, respectively. A much better solution would be to use a buck-boost regulator that can accomplish both modes in one step.

Optimizing Board Space
With regards to the size of the design solution, small power ICs don't necessarily mean small solution sizes. We have to make sure that the passive components, such as the capacitors and inductors, are optimized as well. Also, one rule of thumb I have is that the power IC for a handheld solution should not be the largest component, in the x, y or z dimension, of the critical path.

Focusing on the intangibles: ease of use and time to market
Every power-IC vendor and customer knows that efficiency and design-solution size are critical to a handheld design. In fact, these should be considered prerequisites for next-generation handheld designs. So, what else can a power-management device bring to the table?

One factor is ease of use. Handheld-device designers are not power experts and would prefer simpler solutions. For example, it is simpler to design in an inductor-less charge-pump switching regulator compared to a magnetic solution, since the designer does not have to deal with larger size, extra layout time and, of course, the noise generated by an inductor.

It is necessary to provide development tools and application notes to help those lonely designers trying to invent the next iPOD-like success in their garage. Design tools have been neglected in the portable market, with the majority of the vendor resources focused on direct support for large-OEM customers. More resources need to be dedicated towards software and web-based tools to help the bulk of the handheld designer community.

The handheld market has very aggressive development-time cycles to meet the ever-changing needs of the consumer. Portable-device designers would appreciate ICs which minimize design time. A handheld design solution is a dynamic entity, revising itself over and over again with the latest features and applications. This translates into a need for new voltage-rail and current-output values. It is very inefficient for a designer to search for new power solutions, evaluate them, re-design their boards, and test the new system each time.

It is also important to have power ICs which have a certain degree of configurability. Digital interfaces such as I2C can help the designer change voltages and current, among other parameters. However, the I2C interface requires additional software to be written, which is a rare event in consumer electronics design. So, we have to be innovative in developing analog interfaces to allow designers to modify their solutions or, even better, we need to provide power solutions that adapt to the changing need of the end application.

Traditional specifications for power regulators, such as efficiency, have reached a saturation point. There is little benefit to investing in a switching regulator which gives 96% efficiency compared to 95%. In contrast, a large percentage of power challenges of the handheld designer still remain unresolved. There are very good power-management ICs available today that can be of greater usefulness to the system designer, if they are targeted at the right problems.

In addition, there is a great opportunity for power-management specialists to define new devices that will enable higher-performance handheld devices. The next generation of handheld power-management ICs will not only be efficient power regulators but also excellent problem solvers.

About the Author
Vik Sangha is a product marketing engineer in the Portable Power Systems Group at National Semiconductor Corporation. He is responsible for defining next-generation power solutions including magnetic buck regulators, switched capacitors and linear regulators. Vik has a Bachelor of Science in computer engineering from Union College in Schenectady, NY. He has been with National Semiconductor since 2002.