Advertisement

Article

REVIEW: ARM-powered silicon eases point-of-load power source design

TI Unveils Next-Generation Digital Power System Controllers for Communications and Computing Applications

Multi-Output, Multi-Phase Controllers Make Power Systems More Adaptable, Energy Efficient

DALLAS—Texas Instruments Incorporated (TI) introduces its third-generation Fusion Digital Power controllers and new plug-in modules that more intelligently manage today's power systems. The highly configurable and feature-rich products digitally manage up to four independent digital-control loops and up to eight phases, while improving energy efficiency up to 30 percent during light load conditions.

Leading telecom and server equipment suppliers, such as Sun Microsystems, continue to look for new ways to manage multiple power phases and respond quickly to changes in the system. TI's family of UCD9240 integrated power system controllers provide the highest density and performance features to quickly adapt to what a system needs.

“Tomorrow's servers will require better power management capabilities that increase density and improve the system power efficiency over the range of operating conditions, while maintaining overall system reliability,” said Ansu Chakrabarti, senior manager of System Technology from Sun Microsystems. “New developments in digital power technology, such as the UCD9240 from Texas Instruments, will allow Sun to offer servers with significantly improved levels of power system optimization.”

Digital Power Controller for Point-of-Load Systems

TI's four-output, multi-phase UCD9240 power system controllers implement digital pulse width modulators (PWM) with 250 picoseconds resolution, and are fully configurable via a graphical user interface (GUI) for monitoring, control and management for DC/DC point-of-load power conversion. GUI configuration allows a designer to intelligently manage the power supply's voltage and current thresholds and response, soft start, margining, sequencing, tracking, phase management, loop response, fan control and many other features.

The UCD9240 incorporates the Fusion Digital Power peripheral, which performs full-digital loop control while supporting switching frequencies of up to 2 MHz. The controller supports up to 100 PMBus interface commands for control, configuration and management of the power supply, while requiring a minimal supply current as low as 40 mA during operation.

Phase Management Capability

The UCD9240 controller incorporates a unique phase management feature that enables the power supply to operate at high efficiency over the range of the load. Phase management allows the user to turn on or off phases of the power supply so that only the phases required to power the load are enabled. In addition, the UCD9240 allows the user to optimize the loop response for the operating condition and meet acceptable transient response over the load range.

PowerTrain Power Modules

In addition to the new controller family, TI introduced two new PowerTrain plug-in modules that further simplify the DC/DC converter design by providing a high-degree of configurability when used with the UCD9K family of controllers. The PTD08A010W and PTD08A020W 10-A and 20-A modules integrate the inductor, FETs and TI's UCD7230 driver with current sense capability plus integrated short circuit protection to provide stable and reliable operation of the power supply while protecting the system.

Configurable Design Tools Make Digital Power Easy

TI's configurable design tool helps designers configure and set specific criteria to monitor and control the power system ” with no programming required. The free design tool works with all UCD9K Fusion Digital Power controllers, and provides real-time monitoring, modeling and simulation features to manage the power system digitally.

Expanding Digital Power Portfolio

TI provides a broad portfolio of digital power integrated circuits that enable digitally controlled power systems with high system intelligence and performance in an easy-to-use, intuitive development environment. From its Fusion Digital Power series of UCD9K and UCD7K controllers and power supply drivers, to the high-performance, fully programmable, DSP-based TMS320F28x controllers, TI's digital power solutions are optimized for applications ranging from point-of-load to high-power AC/DC conversion.

Pricing and Availability

Samples of TI's UCD9240 power system controllers are available in a 64-pin QFN package. Suggested resale pricing for the UCD9240 is $5.95 in quantities of 1,000 units. The PTD08A010W and PTD08A020W 10-A and 20-A PowerTrain modules are sampling today with a suggested resale price of $8.50 and $12.90 in quantities of 1,000 units. Volume production for all devices is expected in the third quarter of 2007. An evaluation board, application notes and data sheets are available at www.ti.com/digitalpower.

These highly integrated devices from Texas Instruments once again expand the company's portfolio of power controllers, encompassing TI's UCD9080 s (in production), the F28044 s (also in production), and the UCD91xx family (sampling and supported with eval boards).

The news of TI's PTD08A010W and PTD08A020W high-current PowerTrain plug-in modules also enhance the mix.

Dynamic Adaptation

Not mentioned in TI's press release (on the left) is the fact that the UCD9240 4-output POL (point-of-load) chip adapts to system needs in a dynamic manner. That happens largely thanks to its flash-enhanced non-volatile memory.

Also not mentioned is the fact that the 80-pin TQFP -packaged UCD9240 packs an internal ARM (Advanced RISC Machines) core. In addition to the ARM-7 intelligence, the chip integrates a linear regulator, oscillator, and soft-start circuitry. This is one highly integrated device, as the block diagram reveals.


Click for larger block diagram

The device enables tracking, sequencing, and phase management, all calculated to maintain high power-supply efficiency over wide load ranges, and can run supplies at switching speeds to 2-MHz. It does this while pulling only about 25-mA at 3.3-V.

Partitioned Power

The PMBus -equipped UCD9240's multiple outputs also let you partition your overall power circuitry. You could, for example, let a single UCD9240 handle two 10-A outputs, a 20-A output, and a 40-A output, all derived from a single 6-V through 14-V input.

A word about PMBus (Power Management Bus). It's an open-standard protocol with its own command language that's crafted to facilitate communication with power converters and power devices such as the TI UCD9240. PMBus is implemented using the popular industry-standard SMBus serial interface.

PMBus is maintained and promoted by the PMBus-IF (PMBus Implementers Forum), composed of more than thirty companies. PMBus v1.1 , implemented in this chip, supports communication between both analog and digital devices, providing lots of interoperability that can hopefully reduce complexity.

PMBus lets you program, control, and monitor (in realtime) PMBus-compliant power conversion devices. Using PMbus, you can actually closely monitor a power supply's output with a resolution better than 0.5-mV.

In TI's chip, that kind of capability can let you report Vin , and Vout on each rail, as well as Iout on each power stage phase. You can also monitor temperature.

Eval Board And Windows Software

TI's 4-output device is supported in development by a 4-output evaluation board. The eval board, which is GUI (graphical user interface) configurable using your PC, lets you set operating margins, operate soft starts and soft stops, and accommodate tracking, sequencing, and fault responses.

The eval board is, in turn, supported by TI's Power+ Digital Power Developer Windows software. The software is what gives you a window into the chip's realtime system diagnostics, using design-time data.

Intermediate data can also be collected during your power supply's design and check-out, and you can gather burn-in data and performance data too, as you proceed.

TI's software also supports remote reporting, with locally buffered data used for troubleshooting and monitoring. A realtime buffered data selection can be used to view key performance parameters.

In use, the UCD9240's switching frequency, output configuration, and feedback compensation are programmed through the tool's GUI. This permits one part to support multiple converter arrangements, and lets you dynamically adjust performance to meet a range of POL applications.

High-Res PWM

Within the silicon itself, high-speed digital control loops—with individual digital 3-pole/3-zero compensators—are complemented by high-res digital PWM stages. A UCD9240 contains four such PWM controllers, and each can be MUXed to drive from one to eight power stages.

Each controller consists of a 10-bit setpoint DAC (digital-to-analog converter), a diff-amp, an error A/D (analog-to-digital converter), a digital compensator, and a digital PWM engine.

The reference for each control loop is set by the DAC. It generates a differential output voltage that ranges from zero to 2.5-V. this level is then applied to the chip's diff-amp, where it subtracts the differential output sense-voltage from the DAC reference voltage.

The output of the diff-amp is then applied to the error A/D, which comprises a 6-bit flash converter that imparts a resolution of from 1-mV to 8-mV (resolution of the error converter is adjusted, depending on the operation of the power supply).

Sophisticated Filtering

The output of the error A/D then feeds the chip's compensator stage. It comprises a digital filter consisting of a second-order IIR (infinite impulse response) filter, cascaded with a first-order IIR filter.

As you'd guess, the coefficients of the filter sections are programmable through the PMBus. Moreover, several banks of filter coefficients can be downloaded to your device, which then automatically switches them in, depending on the operation of the power stage. Naturally, the design tool assists you in defining the compensator's coefficients.

Indeed, the Power+ Digital Power Developer Design Tool lets the compensator be described in terms of pole frequencies, zero frequencies, and gain for the control loop.

In addition, the tool can be used to characterize the power stage so that compensator coefficients can be chosen based on total loop-gain for each feedback system. The compensator also permits minimum and maximum duty-cycle to be programmed by issuing an appropriate PMBus command to the chip.

Monitor And Manage

In addition to implementing digital control loops, the UCD9240 can also monitor and manage power-supply operating conditions. It then reports condition status to your host computer through the PMBus port. Again, all management parameters are configurable through the PC-based Power+ Digital Power Developer software tool.

The tool also lets you configure the digital control loop characteristics, and generate expected performance, by displaying Bode plots for each controlled power stage.

On multi-phase power stage outputs, the UCD9240 uses digital current balancing. The average current in each phase is therefore monitored, and the duty-cycle for each phase is adjusted to balance the average current.

As TI's press statement notes, the UCD9240 chip additionally supports shedding one or more phases (ganged power stages), based on average current demand. When a phase is dropped or added, the device automatically adjusts the phase of each PWM output. That minimizes output ripple, as well as any needed change in loop compensation.

The PWM Engine

The output of the compensator feeds the previously mentioned PWM engine. The PWM stages deliver the pulse-width-modulated gate drive outputs. In operation, the compensator calculates the necessary duty-cycle as a 16-bit number (a value from 0 to 1). This value is multiplied by the period to generate a ramp threshold.

The digital ramp is produced continually in the PWM engine. As motioned, resolution of the ramp is 250-ps. When digital ramp values cross the threshold calculated by the compensator, the PWM gate-drive is brought inactive.

When the UCD9240 is configured to drive multiple power stage circuits from one compensator, each gate-drive output pulse width is adjusted to correct for current imbalance between the connected power stage sections.

That's accomplished by monitoring current using the 12-bit A/D, and increasing the pulse width of the PWM signal driving the power stage with the lowest current, and decreasing the pulse-width of the PWM signal driving the power stage with the highest measured current.

Multi-Chip Syncing

Each PWM engine can also be synced to another PMW engine, or to an external sync signal. In operation, an input sync can cause a PWM ramp timer to re-set. Sync signal outputs from each of the four PWM engines occur when the ramp timer crosses a programmed threshold. In this way, the phase of multiple power stage drive signals can be tightly controlled. The sync is programmed through a PMBus command, as is the switching frequency.

TI's latest silicon, and its wealth of support tools, represents a step-function boost in the development of POL supplies. It's worthy of your attention.

Click here to review an engineering datasheet (in Adobe Acrobat .PDF format).

For more details, contact Texas Instruments Inc., Product Information Center, 13532 No. Central Expressway, Dallas, Texas 75243-1108. Phone: 972-644-5580. Fax: 972-927-6377.

Texas Instruments , 972-644-5580, www.ti.com

0 comments on “REVIEW: ARM-powered silicon eases point-of-load power source design

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.