Power Management Units Provide Versatile Power Delivery

July 23, 2008
Designers of portable and handheld appliances have been adding new and very exciting features to their already feature-rich products

Designers of portable and handheld appliances have been adding new and very exciting features to their already feature-rich products. This incredible move toward such a never- before-seen level of design complexity and sophistication makes the total system design both in hardware and software very elaborate and demands great attention to every detail.

These appliances must also achieve long battery life under all operating conditions, which places great demands on the power delivery subsystem. In turn, these demands have driven the development of highly complex, highly functional, high-power, high-density power management solutions.

A number of single-IC solutions to meet these very demanding power requirements are available now on the market with varying degrees of completeness. Here, I will discuss some of the features these ICs provide and discuss how some offer a complete and comprehensive power solution for several mobile and handheld applications.*

All consumer portable applications operate from some form of a battery that requires charging periodically. Batteries require a very strict charging methodology to guarantee successful charging while maintaining safety of operation. CPUs employed in these portable devices require a regulated core voltage that offers excellent transient response and high-power conversion efficiency. The myriad of other functions found in portable products require a number of low dropout regulators (LDOs) to power their electronics.

It is obvious to any practicing design engineer that implementing such a power management subsystem in a discrete solution would require several LDO ICs, one battery-charger IC, and one or more synchronous buck converter ICs plus an I2C controller and glue logic. This clearly represents a solution that requires very large pc-board footprints relative to the total system implementation.

The discrete approach also will require high cost, long design and debugging cycles, and most importantly, it is unlikely to produce a fully optimized solution for the specific application. In contrast, a dedicated power management unit (PMU) implemented as a single IC can provide fully optimized building blocks to fit a range of portable applications.

Naturally, the PMU approach requires attention to certain design issues. With so many individual functions integrated on one IC, designers must pay attention to pc-board layout to maximize the transient response of the buck converter without introducing any crosstalk on the feedback loop, other functions within the PMU and in the rest of the circuit. Layout designers should also place circuits fed by each converter as close as possible to these converters’ output to minimize losses.

ICs that were developed to communicate with a host chipset via I2C interface are of particular interest. Through the I2C bus, circuit designers can program many of the features built into the device such as charger settings and output voltage.

If the output voltages can be adjusted through the I2C bus, then the circuit designer can optimize the performance of the power subsystem on the fly. This need for on-the-fly optimization could be in response to low battery, high temperature, battery aging and load conditions.

Power-up sequencing also is a key requirement in many products. There are many ways this can implemented in a PMU such as using independent enables and/or I2C interface. These can be of great use during host self-testing and sleep modes, which helps the user to design robust solutions.

Over a year ago in my column, in the article “High-Density Power Modules: The Way of the Future,” I discussed why the integrated power module approach makes sense from the designer’s point of view. Now, with the proliferation of these devices and the wide acceptance of this approach by the portable appliance manufacturers, one may realistically expect that in the near future we should see even more sophisticated PMUs offering a range of capabilities, features and miniaturization at a scale never seen before. This will allow OEMs to continue to offer new handheld devices that will be widely popular with consumers around the world.

*Editor’s note: The author’s company is a provider of both PMUs as described in this article and discrete voltage regulators.

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