[Technology Report]
Next-Generation Multifunction Power ICs Help Shrink Mobile Systems
To meet size constraints, a single IC functions as a power subsystem-on-a-chip by integrating combinations of linear and switching power sources, battery chargers, and even audio amplfiers.
With mobile equipment manufacturers demanding ever smaller and lighter handheld systems, the trend is to create smaller ICs that offer greater functionality. However, meeting those functionality, size, and weight requirements becomes a more difficult proposition in power-oriented applications.
For instance, switching regulators must be very efficient, particularly when multiple switchers are integrated into an IC. Battery- charger circuits must be efficient. Also, chip layout must ensure that there are no "hot spots" and electromagnetic interference (EMI) is controlled. On top of that, many handhelds operate from a single lithiumion/ polymer cell. Despite these difficult design issues, many IC manufacturers have responded with devices that meet the system requirements.
Take Linear Technology's LTC3555, the first in a family of multifunction power-management solutions for Li-ion/polymer battery applications. It integrates a switching PowerPath manager, a standalone battery charger, an ideal diode, I2C control, three high-efficiency synchronous buck regulators, and an always-on low-dropout regulator (LDO) (Fig. 1).
The LTC3555's PowerPath control seamlessly manages power flow between an ac wall adapter or USB port, Li-ion battery, and system load while its "instant-ON" operation ensures system load power even with a dead or missing battery. For fast charging, the LTC3555's switching input stage converts nearly all of the 2.5 W available from the USB port to charging current.
This enables up to 700 mA from a 500-mA limited USB supply and up to 1.5 A when wall-powered. An internal 180-mV ideal diode plus optional external ideal diode controller provide a low-loss power path, further minimizing heat generation and maximizing efficiency.
The LTC3555's three integrated synchronous buck regulators feature 100% duty-cycle operation and can deliver 1-A/400-mA/400-mA outputs, respectively, with adjustable output voltages down to 0.8 V. The internal low-RDS(ON) switches deliver efficiency as high as 94%, maximizing battery run time.
In addition, Burst Mode operation optimizes efficiency at light loads with a quiescent current of 35 mA per regulator (<1 mA in shutdown). The 2.25-MHz switching frequency allows use of tiny low-cost capacitors and inductors less than 1 mm in height. Furthermore, the regulators are stable with ceramic output capacitors, achieving very low output voltage ripple.
The LTC3555 features USB-compatible programmable current limiting to 100 mA/500 mA/1 A, while its Bat-Track adaptive output control enables high-efficiency charging and reduces power dissipation. Standalone autonomous operation simplifies design, eliminating the need for an external microprocessor for charge termination. To preserve battery energy, the LTC3555 draws <23 mA from the battery in suspend mode. The charger is compatible with inputs up to 5.5 V (7-V absolute maximum transient for added robustness).
The powerwise interface National Semiconductor's LP5552 is a PowerWise Interface (PWI) 2.0-compliant energy management unit (EMU) for applications such as baseband processors in mobile phones and other portable equipment (Fig. 2). It operates cooperatively with processors using an advanced power controller (APC) to provide adaptive voltage scaling (AVS), which significantly improves processor efficiencies over conventional powerdelivery methods.
The LP5552 is intended for use in a voltage scaling system that lowers the system's power dissipation. Scaling supply voltage with the clock frequency of a processor is a huge power saver. Also, the device supports two types of voltage scaling - dynamic voltage scaling (DVS) and AVS.
DVS systems switch between pre-characterized voltages, which are paired to clock frequencies used for frequency scaling in the processor. AVS systems track the processor performance and optimize the supply voltage to the required performance. AVS is a closed-loop system that provides process and temperature compensation to deliver the minimum supply voltage for any given processor, temperature, or clock frequency.
To support DVS and AVS, the LP5552 is programmable via the low-power, two-wire PWI. This serial interface controls the various voltages and states of all regulators in the LP5552. Both slaves in the LP5552 support the full PWI command set, other than the optional extended register read and write, as described in the PWI 2.0 specification: core voltage adjust, reset, sleep, shutdown, wakeup, register read, register write, and authenticate.
The PowerWise technology is an advanced energy-management solution for energy-constrained digital devices, like mobile phones, PDAs, handheld gaming consoles, and personal navigators. Developed by National Semiconductor in collaboration with ARM, it enables longer battery life, more features, and improved user experience by reducing the energy consumption in digital processors by up to 70%.
Operating from a 2.7- to 4.8-V input, it's compatible with single-cell Li-ion batteries. The LP5552 contains two 88% efficiency, switching dc-dc buck converters that are programmable from 0.6- to 1.235-V outputs. Switching frequency is 3.6 MHz, and output current measures 800 mA per switcher. They supply two voltage scaling domains, and five digitally programmable LDOs are available for supplying additional support circuitry.
Interesting. When did they start producing "ideal" diodes? Where can I get some? Oh, but it's 180mV, whereas I thought ideal would be 0V. So maybe it's "idealer"? Ah, marketing.
Anonymous -November 06, 2007
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