Power Electronics

Portable Power Management Inspires Mega Integration

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As designers of handheld devices pack greater functionality into their products, requirements for power management have become increasingly complex. Products require multiple supply rails, battery charging and a variety of power management capabilities. All of these functions must be implemented with the goal of maximizing battery life, particularly as the functionality of the portable product grows and puts a greater strain on the battery. At the same time, the limited space in the applications demands compact solutions.

These requirements have inspired the development of some surprisingly complex power management ICs. These chips take into account the power management of microprocessors and other functions typically encountered in smart phones, PDAs, media players, gaming units, digital still cameras and Internet appliances.

The power management chips being developed for these applications are a diverse lot. Some focus on integrating just the regulators and power control functions needed in their target applications. Others go a step or two further, implementing a variety of chip-compatible functions for handling audio, lighting and user interface.

A look at a few of the recently introduced portable power management ICs reveals the different approaches being taken and the very high levels of functional integration being achieved. On the surface, these parts look very different. However, there are some common features such as I2C programmability and dynamic voltage scaling that suggest the more widespread application requirements.

One of the new ICs that aims to push the limits of functional integration in portable power management is Freescale Semiconductor's MC13783, which was introduced in December. Within a 247-pin BGA, this power management and user interface chip combines a full audio system, a battery-charger system, a lighting system, five switching regulators, 18 linear regulators, a USB transceiver, a car-kit interface, a touchscreen interface and other functions (see the figure).

Although all of its features may not be required in a particular application, the MC13783 gives product designers a high degree of adaptability, allowing them to scale product features across tiered product families. The goal with this approach is to enable very compact portable product designs, while also accelerating their development.

Among the chip's power management features are dynamic voltage scaling, multimode operation of the switching regulators and user-off support with power-interruption recovery. In addition to its Li-ion battery charger, the MC13783 can maintain the charge on a coin cell used for battery backup.

MC13783's audio system contains a high-fidelity stereo DAC and headphone driver tailored for MP3 or personal media playback. Meanwhile, its lighting system provides white LED backlight drivers for displays, keypad and flashlight, plus tricolor fun lights. For gaming applications, the chip offers applications processor support, a vibrator driver, and power audio and touchscreen capabilities.

The chip also offers dual processor support for flexibility in adding mobile-phone capabilities to convergence devices. The MC13783 improves speakerphone performance by providing power audio and dual CODEC paths for noise cancellation and improved voice clarity. In addition, the device features a USB OTG transceiver with CEA-936-A car-kit support for transferring files, music and graphics (or charging a battery) through a shared mini-USB connector.

The MC13783 is offered as a standalone part or as part of a total platform solution. Platform applications include Freescale's 3G Innovative Convergence i.300-30, Mobile eXtreme Convergence MXC300-30 and MXC275-30 EDGE solution. The device also is well suited for use with Freescale's i.MX31 applications processor. The MC13783 is available now. For more details, see www.freescale.com/pmui.

Meanwhile, Semtech recently unveiled the SC905 family of power management ICs for cell phones and multifunction portable devices. Packaged in 5-mm × 5-mm 32-pin MLP, this chip contains nine ultralow-dropout regulators (LDOs) capable of sourcing up to 300 mA from multiple inputs. The chip's I2C serial interface can be used to program the output voltage and control the enable of each LDO. And because the SC905 can interface with a Semtech battery-charger IC, the host processor also may use the I2C interface to monitor charger status.

Each LDO's output current and output noise is specifically optimized to match the handset's baseband functions — the microprocessor core, analog circuitry, keypad, receiver, transmitter, VCO, PLL, camera and vibrator motor. The SC905 also includes battery-charger control.

Five of the LDOs on the SC905 can generate low-noise outputs in the 2.55-V to 2.9-V range to power noise-sensitive analog circuitry such as audio, RF or oscillator circuits. Three of the other regulators generate outputs in the 1.35-V to 2.9-V range and are designed for powering digital circuits. One additional LDO can drive up to 150 mA at 1.35 V to 2.9 V. This regulator may be used as a general supply or as a vibrator motor supply.

A variation on the chip, the SC905A, offers the same combination of LDOs, but with expanded input/output voltage ranges for select LDOs (output range up to 3.3 V). This capability enables the power management chip to support a larger variety of CDMA chipsets. The SC905A also contains a dedicated enable pin for the vibrator motor regulator and transceiver output.

The SC905 and SC905A come with a power-on control pin for on/off control of the baseband processor, oscillator, keypad and audio. Two other pins are available to power up the devices when connected to a battery charger or hands-free kit.

The SC905 and SC905A both feature six independent input-supply pins for connection from either the battery directly or other power sources, minimizing regulator input-to-output voltage drops and improving overall efficiency. In addition, the ICs feature short-circuit and overtemperature protection.

The SC905 and SC905A are available immediately in production quantities and are priced at $2.44 each in 1000-piece lots. For more information, see www.semtech.com.

Another recently introduced device is National Semiconductor's LP3971, a power management unit for advanced application processors such as Intel's Xscale. Housed in a 5-mm × 5-mm, 40-pin LLP, the IC provides six low-dropout, low-noise linear regulators (LDOs), three buck regulators, a backup battery charger and two general-purpose I/Os. An I2C interface is included to program individual regulator output voltages as well as on/off control.

The buck regulators produce a programmable output voltage from 0.8 V to 3.3 V, and up to 1.6 A of output current, while operating with up to 95% efficiency and ±3% output voltage accuracy. The LDOs produce a programmable 1-V to 3.3-V output with ±3% output voltage accuracy. Three of the LDOs are rated for 150 mA, while the others specify ratings of 30 mA, 300 mA and 370 mA. The input voltage range of the device is 2.7 V to 5.5 V.

In addition to offering efficient power conversion, the LP3971 minimizes power consumption through dynamic voltage scaling, which enables the design engineer to modify the output voltage in real time to match the computing workload and clock frequencies of the corresponding processors.

Other features include a power-on-reset function to protect the processor from input voltage fluctuations, thermal overload protection and overcurrent protection. In the backup charger circuit, an automatic switch accommodates either Li-manganese coin cell batteries or supercapacitors. Available now, the LP3971 is priced at $4 each in 1000-unit quantities. For more information, see www.national.com/pf/LP/LP3971.html.

Another power management device in this category is Texas Instruments' TPS65800, which was unveiled last fall. Within an 8-mm × 8-mm, 56-pin QFN, this chip integrates a single-cell Li-ion battery charger, nine LDOs, two buck regulators, LED drivers and system-management functions. An external host processor may control the TPS65800 via its I2C interface, which can set output voltages, current thresholds and operation modes.

The chip's internal registers hold a complete set of status information, enabling easy diagnostics and host-controlled handling of fault conditions. The TPS65800 can operate in standalone mode, with no external host, if the internal power-up defaults are compatible with the system requirements.

Among the on-chip regulators are six LDOs with adjustable 1.25-V to 3.3-V output, two LDOs with fixed 3.3-V output and one 3.1-V LDO that serves as a real-time clock backup supply. The chip's two 600-mA buck converters generate programmable 0.6-V to 3.4-V output and feature enable, standby mode operation and an automatic low-power mode setting.

The TPS65800's battery charger features thermal foldback, dynamic power management and pack temperature sensing while supporting up to a 1.5-A maximum charge current. Programmable charge parameters enable the charger to run off of either an ac adapter or USB port. Display functions include two open-drain PWM outputs with programmable frequency and duty cycle. These can be used to control a keyboard backlight or vibrator. The IC also includes a programmable RGB LED driver and a programmable white LED driver that powers up to 6 LEDs in series.

In addition, the device offers system management functions such as a dual-input power path with input current limiting and overvoltage protection. There are also power-on reset as well as software and hardware reset functions. Unit pricing for the TPS65800 starts at $6.50 each in quantities of 1000.

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