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Six New Ways to Boost Battery Life

Power management is the key

Randy Frank -- Design News, April 26, 2004

You can never be too rich, too thin—or have enough battery life in your handheld device. Trouble is, with the increasing number of product features, like color displays and cameras in cell phones, the demand for power is going up. Complicating matters is the fact that all of these new and different functions require different voltage levels—making power management one of the most diabolically challenging tasks on the planet. Fortunately for you, there is a whole host of new power management ICs and discrete components designed to make the task a whole lot easier.

Dual High-Efficiency Step-Down DC-DC Converter

Linear Technology Corporation (LTC): LTC3455

Applications: Handheld computers, digital cameras, and MP3 players

Price: $3.95 in quantities of 1,000

Addressing the need for the variety of voltages and added functions in portable devices, LTC recently announced this dual high-efficiency (up to 96 percent) step-down dc-dc converter with a hot swap controller, USB power manager, and a lithium-ion battery charger in a 4 x 4 mm² 24-pin QFN package. The circuitry can provide 3.3V at 600 mA, 1.8V at 400 mA, and a hot swappable 3.3V up to 100 mA from a single cell. A unique capability of this IC is integrated power-path control, which allows it to seamlessly transition between power sources. That means a user can change from charging the battery from an ac adapter to using the Li-ion battery or powering a USB connection, while providing hot-plug protection for the USB port and wall adapter. The accurate USB current limit is pin selectable for either a 100 mA or 500 mA limit, as well as a suspend mode where current drawn from the USB pin is less than 50 µA.

Triple Voltage Output LCD Supply with Linear Regulator

Texas Instruments: TPS65100

Applications: TFT LCD displays for notebooks, monitors, portable DVD players, tablet PCs, car navigation systems, and industrial displays

Price: $2.70 each for 1,000-unit quantities

The recently introduced TPS65100 provides all three voltages required by thin film transistor (TFT) LCD displays. The main output is a 1.6-MHz fixed frequency boost converter that provides the source drive voltage (up to 15V at 400 mA) for the LCD display. Other voltages include the negative supply that can be as low as -12V at 20 mA and a positive supply up to 30V at 20 mA. A linear regulator controller with an external transistor provides a regulated 3.3V output for the digital circuits. An integrated VCOM buffer in the TPS65100 powers the LCD backplane. The supply is available in TSSOP-24 and QFN-24 PowerPAD Packages.

Analog Baseband and Energy Management ASIC

STMicroelectronics: STw4200c

Applications: CDMA2000

Price: Available from ST for this wireless ASIC devices

ST recently announced a 3G STw4200c analog baseband and energy management IC that integrates power management, battery and charger control, and monitoring functions, as well as voice and radio sigma-delta analog/digital (A/D) and D/A converters and control for several other functions in a single IC. Sigma-delta converters are among the components that are very challenging. The sigma-delta converters' oversampling and noise-shaping abilities allow them to perform digital filtering and decimation. And a sigma-delta converter ADC can achieve high resolution with low bandwidth. ST estimates that by using this chip, at least 20 percent improvement over other known solutions is possible for total energy control.

In addition, the chip has voice codec (code/decode) A/D and D/A converters with programmable attenuation and gain stages, as well as microphone amplifier, earpiece, and headset drivers. The IC includes seven low-noise baseband low-drop-out regulators for analog, logic, flash, LEDs, the digital baseband core, and the removable user identity module. Drivers for a buzzer, vibrator, keyboard, display backlight, and LEDs complete the human interface functions. The highly integrated STw4200c comes in a 244-pin thin fine-pitch ball-grid-array (TFBGA) package.

Efficient High Side-Power MOSFET Switch

Fairchild Semiconductor: FDZ299P

Applications: Cell phones, PDAs, portable music players, GPS receivers, and digital cameras

Price: $0.66 each for 1,000-unit quantities

No matter how much circuitry is integrated in a complex IC, there are still times that a separate component is required. For switching power, today's advanced trench MOSFET products are the technology of choice for high efficiency in low-voltage applications since they eliminate the junction field-effect transistor found in planar MOSFETs and the associated losses. Combining trench silicon design with BGA packaging frequently used in much higher pin-count IC products, the FDZ299P provides space-and-power-efficient switching. With a gate voltage of -2.5V, the on-resistance is less than 80 mÙ in a 1.5 x 1.5 mm package. To evaluate the performance/size tradeoffs, Fairchild has developed the concept of a footprint figure of merit (FFOM), the product of on-resistance and footprint. For example, the 20V, P-channel FDZ299P's FFOM of 180 offers a 75percent better FFOM compared to a standard TSSOP-6 (3 x 3 mm) device with an FFOM equal to 720.

Now with -4.5V applied to the gate, the FDZ299P's on-resistance is less than 55 mÙ and the total gate charge, Qg, is less than 9 nC providing high efficiency for both steady-state and high-speed switching applications. The thermal transfer characteristics of the BGA package allow the MOSFET to dissipate 1.7W, 0.1W more than the much larger TSSOP-6 package that it can replace.

Small-Package Schottky Diode

International Rectifier: IR140CSP Flip KY

Applications: Battery packs, cell phones, and PCMCIA cards

Price: $0.25 each in 10,000-unit quantities

Due to its lower forward voltage drop compared to other diodes, a Schottky diode is frequently used in dc-dc converters for low-cost, highly efficient rectification. But if the dc-dc converter is not a complete integrated solution, it can pose problems in a portable product. The challenge to engineers is figuring out how to reduce the space required for the dc-dc converters and the load switches, and at the same time deliver the increased power. One of IR's answers is packaging improvements using flip-chip technology to reduce conduction and switching losses. The company recently introduced this 1A, 40V Schottky diode that uses standard BGA or flip-chip technology to take up only 2.25-mm² circuit board area. The device is 86 percent smaller than the popular surface-mount package frequently used for Schottky diodes. The package also has both a low profile (& 0.78 mm) and forward voltage drop (0.38 Vf), so more power can be delivered in the same space.

Tailored Oscillators Cut Microcontroller Power

Microchip Technology: PIC16F684

Applications: Battery-operated or handheld products, sensors, interface, home appliance, automotive, and general-purpose control functions

Price: $1.38 each in 10,000-unit quantities

One of the key factors in lowering a microcontroller's overall power consumption requires focusing on the oscillator selection. Microchip's nanoWatt product family provides the option of different oscillator modes depending on the performance required. The high-speed oscillator operates up to 20 MHz. The microcontroller has a software selectable frequency range of 31 kHz to 8 MHz, and can operate with internal and external oscillators.

Depending on the frequency operation, the PIC16F684 can consume as little as 9 µA while running and requires less than 1 nA standby current when powered down at 2V. Special power-management features in the device include a fast-startup internal oscillator operating at 8 MHz (±1percent), a software-selectable clock speed, software-controlled brown-out reset, ultra-low-power wakeup on change, a lower-power real-time clock timer, and an extended watchdog timer that typically consumes only 1 µA.

With the ability to operate over a wide operating voltage of 2.0 to 5.5V, the MCU is well suited for Li-ion battery applications. In addition the controller incorporates Microchip's PMOS Electrically Erasable Cell (PEEC) flash technology that can withstand one million erase/write cycles on each memory location within an operating temperature range from -40 to 85C for the industrial-rated version.

LTC3455 Block Diagram: Linear Technology's LTC3455 can power three different voltages from a single lithium battery.

Everything but the kitchen sink: ST's STW4200C is a complete analog broadband and energy management ASIC in a 244-pin thin, fine-pitch ball grid array (TFBGA).

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