Chips Attack Barriers to Digital Control

Sep 1, 2008 12:00 PM
By David Morrison, Editor in Chief

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.

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