Designing in portability -

Designing in portability

We are all familiar with batteries these days; they are virtually ubiquitous in a myriad of products and applications. Commonplace examples include your cell phone and notebook computer; however, they are also commonly found in flashlights, cordless tools, MP3 players, portable video gaming devices, hand-held multi-meters, as well as, scientific instruments and a rapidly expanding plethora of healthcare devices.

Accordingly, it will come as no surprise to learn that the global market for portable battery-powered products was valued at an estimated $480B in 2011 and is expected to reach more than $611B in 2016. [Source: BCC Research]. Furthermore, this market is expected to continue its growth expansion through to 2020.

This market can be roughly segmented as follows:

~29% for communication products

~29% for the computer related products

~19% for medical products

~23% for cameras, toys, entertainment, timepieces, lighting, navigation and military products

This diversity has been accomplished because of a unique synergy between the product themselves, the batteries they employ, and the battery chargers and power-management systems that recharge the batteries.

Battery Chemistry & Applications

It is clear that the market for battery powered products is significant but what about the battery chemistry used inside them? Well, the predominant battery chemistry being utilized in this diverse product offering is Lithium-based, which was estimated to be valued at $22.5B in 2016. [Source: Frost & Sullivan]. North America and China have more than half the global revenues for Lithium batteries. What’s more, going forward, this demand will be further fueled by key end-users from the consumer device vendors, industrial goods manufacturers, the grid and renewable energy storage segment and automobile manufacturers. Within the industrial segment, healthcare, power tools and military applications represent the leading usage for Lithium-Ion batteries.

A typical Lithium-ion battery has a discharge profile from a high of 4.2V when fully charged, down to as low as 2.7V when fully discharged. While this is an excellent choice for smart phones and MP3 players, it may not be suitable for portable scientific instruments, power tools and medical healthcare devices. In these instances, multiple cells may be required in order to supply the necessary run-time to be of practical use. This means that 2 to 4 cells will have to be utilized, either in series or in parallel, or a combination of both. As a result, the voltage range of these battery configurations could vary from a high of 16.8V to 10.8V (4 Lithium cells in series), to 8.4V to5.4V (2 Lithium cells in series).

Battery Voltage Conversion & Layout Considerations

High power density has become a primary requirement for DC/DC converters, as they must keep up with ever increasing functional density of electronics. Likewise, power dissipation is a major concern for today’s feature rich, tightly packed devices pushing the need for highly efficient

solutions to minimize temperature rise. For applications where the input voltage source can be above or below the regulated output voltage, finding an efficient compact solution can be a challenge, especially at elevated power levels. Conventional design approaches, such as using a dual inductor SEPIC converter, produce relatively low efficiencies and a relatively large solution sizes.

As already discussed, power-hungry handheld devices, medical products and industrial instruments often require multicell or high capacity batteries to support their ever-increasing processing needs. Many loads require a regulated output that sits within the battery voltage range which necessitates the use of a converter that can both step-up and step-down. Although a SEPIC converter is a viable solution, its large size and modest conversion efficacy are suboptimum for use in portable or luggable products. Thus, a wide voltage range, high efficiency buck-boost DC/DC converter is the ideal solution for longer battery run times and handling multiple input sources.

From the power supply designer’s perspective, it would be great if every time they powered up a prototype supply board for the very first time, it not only works, but also runs quiet and cool. Unfortunately, this does not always happen. A common problem of switching power supplies is “unstable” switching waveforms. Sometimes, waveform jitter is so pronounced that audible noise can be heard from the magnetic components. If the problem is related to the printed circuit board (PCB) layout, identifying the cause can be difficult. As a result, proper PCB layout at the early stage of a switching supply design is very critical and its importance cannot be overstated.

Of course, a power supply designer understands the technical details and functional requirements of the supply within the final product. They usually work closely with the PCB layout designer on the critical supply layout from the beginning. A good layout design optimizes supply efficiency, alleviates thermal stress, and most importantly, minimizes the noise and interactions among traces and components. To achieve these, it is important for the designer to understand the current conduction paths and signal flows in the switching power supply.

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