Power management ICs are progressing quickly towards more digital control and the so-called digital power supply in all its various forms. The pros and cons of digital versus traditional analog designs, set against economic feasibility issues, still have strong supporters on both sides. Few designers, however, dispute the benefits of an ideal "digital" system: High integration, fewer analog parts, faster control response, higher accuracy, tighter regulation, and easy customizing for faster time to market.
Indeed, the concept of a "digital power supply" has come far since Texas Instruments released the first DSP-based developers' kit two and a half years ago. But a self-contained DSP- or microprocessor-based chip complete with digital control loop and all supporting hardware has yet to materialize. In the interim, chip designers are making incremental gains across the gamut of power-management devices as they apply to a supply's control loop directly, programming DC/DC systems and individual converters, and improving accuracy and cutting intellectual property theft in battery management applications.
Control and power
The newest system control chips specifically touted for insertion into "digital power" supply loops include Texas Instruments' UCD7K, -8K, and -9K families, billed as the first chip set of its kind suited to a total (front end to back end) power supply solution. The UCD9K is a DSP-based controller, a semi-identifier of devices in the "digital power" classification, with PWM and logic that can close one or more feedback loops and provides communications and supervisory functions. The UCD7K are MOSFET drivers that interface with the UCD9K or UCD8K. The UCD8K controllers, which requires an outboard microcontroller or DSP engine, integrate the UCD7K devices with a digitally controlled analog PWM controller to close a feedback loop in the analog domain.
Silicon Laboratories' Si8250, promoted as the first fully digital switch mode power controller that delivers both high performance and flexibility, is partitioned into digital control and system management sections, each with its own programmable processor. This partitioning allows the control section to avoid bottlenecks associated with use of a single processor that shares control and management functions.
A second class of "digital power" device are so called power-with-power management chips for (external) control of the overall system. Summit Microelectronics' SMB120, suited for use with a DSP, is claimed the first digitally programmable chip of its kind. This nine-channel DC/DC converter/controller with EEPROM, which claims an unsurpassed integration of power conversion functions, incorporates four PWM DC/DC buck controllers, three DC/DC boost controllers, an inverting buck/boost controller, and a low dropout regulator for powering LCD-TFT displays. Designers digitally program the SMB130's multiple outputs for output voltage and associated power management functions with a few clicks of a mouse. Users can sequence each output, adjust margining, and perform system diagnostics.
Primarion's Powercode PX3535/36/20 also sets claim as a new kind of "digital power" chip set embracing DC/DC power conversion and control. It combines the company's PX3535 six-phase digital controller, PX3536 four-phase controller, and PX3520 power stage. This 120-amp DC/DC converter solution is positioned as differing from previous multiphase products from International Rectifier's X-Phase product, as well as products from Intersil and Analog Devices, all categorized as analog-based. Power-One's Z-series uses a digital approach, but it's suited to general point-of-load (POL) applications. A previous digital product from Potentia also has a different focus, that of digital control/management.
The most noted "supervisory chips" with a decided "digital hook" for minding the overall system are usually identified by their "precision" or "configurable" label. These chips, somewhat removed from the "digital supply" concept, nevertheless are converging to provide such control functions as basic sequencing, tracking, and margining.
Examples include Maxim's MAX6876, an EEPROM-programmable, quad voltage power supply tracker/sequencer that allows the designer to store key system parameters such as voltage thresholds, slew rates, over-current limits, and desired timing schemes. Similar company devices include the MAX6870 and MAX6871. Others include Lattice Semiconductor's Power1208P1 Precision Power Manager IC. This programmable chip, touted for its mixed-signal (analog/digital) advantages, allows power sequencing of up to eight supplies and monitoring of up to 12 supplies. Summit Microelectronics' SMH4046 and SMH4047 Intelligent Power Management controllers, with EEPROM, imply a similar degree of functionality for programming and sequencing of six supplies. Similar devices include the company's SMB110 and SMB113, part of the company's Programmable Power Manager ICs for "digital supplies;" their SMM150, and their SMM764 and SMM766, which sequences and margins up to 30 POLs.
A third component of the digital supply evolution extends to battery management chips. The end goal is the same: high-accuracy monitoring and control. The digital approach also affords device validation to ensure a given battery is suited to meeting the specs of a given portable device, a function difficult to implement economically using an analog approach. New entries include Atmel's microcontroller-based ATmega406, for 2-4 cell lithium-ion packs, billed as the only fully configurable product for economically meeting the high-accuracy and reliability requirements for smart battery packs. Texas Instruments' bq20z8x gas gauge, part of a two-piece chipset, can measure the capacity of lithium-ion battery packs with 99 percent accuracy over the battery's lifetime. Three new authentication ICs from Texas Instruments, Dallas Semiconductor, and Intersil rely on various proprietary and military-based algorithms to thwart the use of so-called counterfeit battery packs, i.e, batteries unsuited to a given portable device.