Needed: Sophisticated Power Management

The increased power demands of 3G phones make improved battery/power management and control circuits more important than ever. While voice usage is demanding, longer continued use of a handset with e-mail, Internet access, and other data activities places a major strain on the power system. Power-management circuits are necessary to ensure the long battery life, talk time, and idle time that today's 2G and 2.5G phone users have come to expect.

At the heart of the power system is the battery. Look for continued use of the lithium-ion (Li-ion) and nickel-metal hydride (NiMH) batteries currently used in 2G and 3G phones that will be found in new sizes and shapes. But new batteries based on other chemistries or technology may come along to help the power problem. Some possibilities are the zinc-air and lithium-ion polymer batteries.

For battery power management, there are four aspects to consider:

• Battery charging: Most users want fast recharges. This is possible with the new Li-ion and NiMH batteries. Both types, though, require critical charging voltages and currents to ensure that the batteries aren't damaged during recharging.
• Voltage regulation: Power to all circuits must be regulated, of course. But multiple voltage levels will be required, which means that multiple regulator chips or special chips will be needed to provide the desired voltages. High-side regulators and/or dc-dc converters are a must. Many of the newer RF and support chips already contain low-dropout (LDO) regulators, making extra regulator chips unnecessary.
• Shut-down circuits: Power-management chips will allow major parts of the phone circuitry to be shut down during idle times. This conserves battery life.
• Power control: Many new RF and processor chips have built-in power control. An input line to the chip tells the chip to shut down. Such chips make power management easier to implement. And, they save costs and design time.

While power-management and control circuitry will be necessary for each phone, most designs can be implemented with the many new chips that exist from familiar vendors. Custom chips are made possible through a vendor that modifies or enhances an existing chip. Given the usual high volume of phone sales, even custom chips can be inexpensive.