Electronic Design

Digital-IBA Controller Mophs To Monolithic

This second-generation controller handles up to 32 digital POLs, four simple LDOs, fans, and so on.

WITH EXPANDED CONTROL CAPABILITIES AND A SHRINKING footprint, Power-One's digital-IBA (intermediate bus architecture) controller goes from a module to a chip—with no change in price. The IBA scheme manages and controls power distribution to individual loads on circuit boards in complex systems.

At first glance, the controller-on-a-chip may seem like an incremental development. But with recent announcements concerning PMBus-compliant products and Vicor's factorized power architecture, it really means the horse race is on.

The racetrack opened in 2004, when Power-One introduced a custom package of products for digital control for the IBA. Its initial Z-system products consisted of point-ofload converters (POLs), a power-management module, a single-wire bus to interconnect them, and friendly GUIbased software to make the system simple to use. They offered total control over output voltage, output tracking and sequencing, switching frequency (0.5 to 1.0 MHz), interleaving, feedback-loop compensation, and active digital current sharing that can provide energy from multiple paralleled Z-POL converters.

The Z-system's key element is the synchronization/data (SD) line that constitutes the Zbus, which synchronizes all of the Z-POLs to a master clock in the manager chip and simultaneously carries bidirectional data between POLs and the digital power manager (DPM). Power-One says that using its controllers and POLs completely eliminates the need for external components for power management.

For some time, the company stood alone in the digital IBA arena. Meanwhile, most other vendors continued to provide basic POLs with limited analog control of turn-on/turn-off sequencing and voltage ramp-up.

At last winter's APEC conference, it even looked as if Power-One might be backing off a little as it introduced a line of hardware-configurable "No-Bus" Z-POLs with a limited range of capabilities. At the APEC show, though, Power-One executive vice president Dave Hage assured me that the company was in it for the long haul and that it would match its competitors' POL prices to prove it.

Of late, several companies have to some extent validated Power-One's original vision by announcing digital-IBA POL and controller products, albeit products based on the PMBus standard.

There's a subtle difference there. The Power-One controller talks to the outside world via I2C, but it interacts with Z-POLs via the company's proprietary Z-bus, which offers board-routing advantages. I2C real-time reporting from the controller consists of output voltage and current, as well as Z-POL temperature data.

Over the months since APEC, Power-One has moved ahead with its vision. The company recently introduced its ZY7120. Rated for 20 A, this fullfledged Z-7000 POL is the eleventh product in the series.

PRODUCT DETAILS Power-One's monolithic Z-series DPM controller, the ZM7332, can deal with 32 of the company's Z-POLs as well as with up to four more basic regulators, even analog LDOs. The ZM7332 comes in a 9- by 9-mm, 64-pin QFN package.

In a typical application, four groups of Z-One POLs—a "group" comprising one or more POL converters interconnected via OK pins—reside in the system (see the figure). Grouping POLs is optional. It lets users program advanced fault-management schemes and define margining functions, monitoring, startup behavior, and reporting conventions.

Externally, users can change programmable parameters at any time during product development and service via the I2C bus from the host system-and/or via Power-One's ZIOS GUI, running on a PC. The DPM can trigger an optional crowbar circuit and provide undervoltage and overvoltage protection for the intermediate bus voltage. The host system also can control the DPM via its interrupt inputs, which can be configured as a hot-swap trigger for a group of POLs as well.

AUXILIARY DEVICE CONTROL Auxiliary devices managed by the controller could be analog POLs or LDOs, or anything that requires on/off control or monitoring. They're treated just like ZOne POL converters. Each has an address and is assigned to a group. Polarity of the enable signals as well as fault data from the auxiliary devices can be programmed. The same is true for turn-on and turn-off delays.

Pricing for an eight-node controller is approximately $10 each for a quantity of 1000 pieces.

See associated figure

Power-One
www.power-one.com

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