Power Electronics

Chips Attack Barriers to Digital Control

In diverse applications, digital-control techniques have the potential to reduce component counts, while improving key performance parameters such as efficiency. However, barriers such as controller cost and the established nature of existing analog-based designs can prevent the adoption of digital control in some products. In response, chipmakers are developing new devices to overcome these obstacles.

For example, a family of 32-bit microcontroller units (MCUs) from Texas Instruments (TI) is lowering device cost, so that real-time control can be implemented for the first time in a variety of cost-sensitive power-management applications. Meanwhile, two digital multiphase PWM controllers from CHiL Semiconductor are challenging analog-based PWM controllers in advanced voltage-regulator-module designs by delivering high efficiency over the load range in combination with fast response to transients.

Real-Time Control for Greater Energy

The Piccolo TMS320F2802x/F2803x series 32-bit MCUs from TI are designed to bring real-time control to cost-sensitive applications. Real-time control makes possible greater system efficiency and precision through the implementation of advanced algorithms for industrial, consumer and automotive applications, such as solar-power micro-inverters, LED lighting, white goods appliances and hybrid automotive batteries.

“The combination of 32-bit performance, enhanced peripherals and small package sizes allows designers to add real-time control and system management using just one microcontroller to applications that could not afford it previously,” says Keith Ogboenyiya, TMS320C2000 marketing manager at TI.

Piccolo F2802x/F2803x controllers can replace multiple electronic components to lower overall system cost while enabling advanced power management. For example, in a variable-frequency air-conditioning unit, a single F2802x/F2803x controller can control two electric three-phase motors and perform power-factor-correction calculations.

For lighting applications, where LEDs can increase energy efficiency by 50% versus high-pressure sodium lamps, F2802x/F2803x-based LED control systems offer intelligent current control and easy system networking. Those capabilities bring down system complexity, and the cost of managing color mixing and temperature control required for white LED systems. Piccolo MCUs also offer the performance and integration to implement power-line communications for streetlight networks that allow cities to pinpoint power outages, and centrally manage and adjust lighting based on time of day, traffic or weather conditions.

In solar-energy applications, Piccolo MCUs enable higher efficiency and greater control for solar panels. Typical solar-power systems use one inverter across multiple panels, but initial investigations have shown that individual micro-inverters connected to each solar panel within a system can drive higher power-conservation efficiencies. Micro-inverters maximize the output of each individual panel, compared to system-wide inverters that maximize the average output of the panels as a complete system.

The Piccolo MCUs feature advancements such as a programmable, floating-point control law accelerator (CLA) designed to offload complex high-speed control algorithms from the main TMS320C28x CPU. The CLA, which will be available starting with the F2803x series, frees the CPU to handle I/O and feedback loop metrics, resulting in up to a fivefold performance increase for common closed-loop applications.

TI's enhanced pulse-width modulators (ePWMs) support high resolution with frequency modulation down to 150 ps, to enable more control over harmonics and reduce sample-to-output delay, a critical factor to avoid missing the falling edges of signals. At 4.6 MSamples/s, Piccolo devices' on-chip 12-bit ADC is up to four times faster than the competing devices, says the company.

Two on-chip oscillators operating at 10 MHz each with ±1% accuracy eliminate the need for external oscillators and their associated cost. In comparison, many MCUs integrate ring oscillators, which have drift as high as 50%, rendering them unsuitable for reliable communication interface clocking.

Piccolo oscillators also offer triple redundancy with on-chip self-test features to help designers achieve system-level safety certifications such as the IEC-60730 safety standard required for white goods in Europe. The simple power architecture eliminates the need for external power ICs and uses a single 3.3-V supply with internal regulator down to 1.9 V, while providing brownout protection and power-on reset.

The first Piccolo MCUs, the F2802x series, will be available for sampling in December and will include 40-MHz to 60-MHz variations, up to 128-kbyte of Flash memory, 12-bit ADC, ePWM and peripherals such as communications protocols, on-chip oscillators, analog comparators and general-purpose I/Os. More device introductions in 2009 will offer higher performance and memory sizes, the CLA, and LIN and CAN communications peripherals. The MCUs are code-compatible with the existing C2000 devices, which provide higher performance and additional features.

Server and Gaming Applications

CHiL Semiconductor has announced two digital multi-phase buck controllers for VR11.1-compliant server and gaming/enthusiast desktop PC applications. Described as the first digital controllers to offer up to eight-phase control, the CHL8316 and CHL8318 controllers use a number of innovative digital-control techniques to achieve more than 90% efficiency across virtually all load ranges, according to the company. To support these controllers, the CHL8510 high-frequency MOSFET gate driver is also being introduced.

“By optimizing our architecture for fast transient response and coupling that capability with up to eight-phase control and several new innovative digital-control techniques, the CHL8316 and CHL8318 controllers offer data center managers and gaming/enthusiast desktop users unprecedented advantages in terms of power efficiency, performance and thermal management,” says Larry Spaziani, vice president of marketing for CHiL.

Many users are beginning to monitor efficiency at the system level. Data center managers can now track server power savings from virtualization or other conservation techniques on a control panel while energy-conscious individuals can visualize power savings on their desktop monitors. CHiL's products provide detailed, accurate SMBus power, current and efficiency information needed for users to easily manage energy-saving efforts.

The CHL8316 is an Intel VR11.1-compliant digital multiphase buck controller that supports up to six programmable interleaved synchronous buck phases. Using a graphical user interface, designers can digitally configure the switching frequency of each phase from 200 kHz to 1 MHz, as well as configure other device settings. The settings are then stored in nonvolatile memory embedded on chip.

To address the fast transients in today's VR11.1-compliant CPU designs, the CHL8316 incorporates an optimized ADC that responds to a very fast transient of >2000 A/µs, reducing capacitance and saving board space and component cost.

By digitally controlling current across six programmable synchronous phases, designers can use the CHL8316 to optimize power efficiency at high load conditions. As current drops, the CHL8316 automatically detects and dynamically reduces the number of phases to further improve power efficiency. A variable gate drive reduces MOSFET gate losses and improves efficiency at lower operating currents. Finally, these products report the operating voltage, current and efficiency through an SMBus, allowing system-level control of power management.

“At currents ranging from 30 A to 40 A, we simultaneously meet transient-control requirements and increase server power efficiency by about 8%. This results in a 150-W reduction at the voltage regulator [VR] level alone on a typically configured blade server,” says Ram Sudireddy, founder, president and CEO of CHiL Semiconductor.

To manage heat dissipation, the CHL8316 adds an external temperature sensor. In addition, a VR HOT function communicates heat levels to the CPU and an overtemperature-protection (OTP) circuit automatically shuts down VR PWM signals when the operating temperature exceeds a second threshold. The CHL8316 also features a current-balancing algorithm that automatically balances current across the IC's six phases during both dc and transient operation, to optimize thermal management.

The CHL8318 adds several capabilities to support higher-performance server and gaming/enthusiast desktop applications. Eight-phase control offers faster transient response and better power efficiency. Custom digital overclocking features allow users to extend the voltage range up to 2.3 V, while VID scaling and offset controls and load-line adjustment features offer additional performance enhancements. Importantly, none of the gaming features require additional external components.

The CHL8318 features the same power-efficiency capabilities found on the CHL8316. Using eight-phase control for high load conditions, along with dynamic phase control and adjustable gate drive for mid-to-low load conditions, designers can achieve better than 90% power efficiency across virtually all load conditions with the CHL8318.

To control the large amounts of heat generated by its overclocking functions, the CHL8318 also adds advanced thermal-management capabilities. Three external temperature sensors support more comprehensive monitoring and control of phase current to balance temperature variations. In addition, the controller adds the same programmable VR HOT and OTP features and the automatic thermal balancing capability as on the CHL8316.

To support the rapid development of VR solutions, the CHL8510 driver IC is designed to support these new buck controllers. The driver offers fast tri-level disable for the power status indicator signal in VR11.1 designs and LVCC down to 5 V for variable gate-drive functions.

In 1000-piece quantities, the six-phase CHL8316 controller is available in a 48-pin QFN and is priced at $2.49 each; the eight-phase CHL8318 controller is available in a 56-pin QFN and is priced at $3.29 each; and the CHL8510 MOSFET driver comes in a 10-pin DFN and sells for $0.49 each. All three devices are specified across the 0°C to 85°C range.

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