Digital control for power conversion and management - Power Circuits - Circuit Diagram

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This article will discuss extensively the technical aspects of digital technology applied to power conversion and management to meet market trends and demand in different market segments. We will also talk about the application and challenges of this technology over analog control.

Power conversion is part of the operation of the power system (feedback loop), while power management covers operating modes, synchronous tracking of start/stop delays, edge margins, and phase-locked (interleaved) functions for parallel operation and system communication.

Over the years, the definitions of "simulation" and "digital" have become somewhat blurred. To avoid confusion, “analog” in this paper refers to “continuously variable physical quantities”, while “digital” refers to “discrete variables”. Because of the characteristics of digital technology, we can store data, perform operations, and communicate effectively.

Until now, the actual processing of voltage and current in power conversion has always been in the field of analog rather than digital, but the control can be analog or digital. Since the control is not completely digital, it is necessary to set the analog-to-digital converter in the feedback loop. So what are the benefits of digital technology?

technology

Digital technology is everywhere in our daily lives. But only about four years ago, this technology was fully applied to the field of power conversion and management.

Characteristics

The most outstanding advantages of digital technology are memory applications, including three basic levels of access: plant-level access for registers that contain internal calibration data and look-up tables for the controller (not accessible to the user); To choose the controller topology that manages the topology and control modes (voltage, current, and hybrid) and provides different fault protection features (users can access it with a password); and monitor and control (accessed via the PMBus protocol). Complete data storage capabilities allow designers to optimize designs and even reuse them on different projects.

The strength of digital technology in terms of storage derives another advantage – communication capabilities. Communication functions through I2C give the controller the ability to calibrate and program, as well as perform different functions in real time, including control, monitoring, status monitoring, remote identification and diagnostics. Other features include different intensity adjustments during transmission, including resolution (number of digits), calibration (analog-to-digital conversion, external inductor), output voltage/current setting, and protection limits (voltage, current, temperature).

Time adjustment features include frequency conversion, delay, and phase adjustment. Control/management functions include operational mode transitions (start/shutdown, pulse train, pulse skip, pulse frequency modulation, pulse width modulation, phase number), self-test and output voltage conversion (edge). The flexibility of time adjustment and control all contribute to the reduction of electromagnetic interference, a feature that is completely unimaginable in a simulated application environment.

The advantages of digital technology may vary depending on the need to fine-tune the different market segments, but several logical elements are required in the implementation process.

Type of logic

When we choose the right logic for an application, flexibility, speed/bandwidth, and cost constraints are the deciding factors. These include digital hard-wired logic (state machine) PID control and digital pulse width modulation (PWM); digital hard-wired logic PID control and digital PWM + non-volatile memory; hybrid = analog PWM + digital interface (generally called " Digital package"); microcontroller (mC); digital signal processing (DSP) and digital control processing (DCP), and includes the best combination of DSP and mC.

Most digital integrated circuits include power conversion control and power management. The power conversion control (feedback loop) can work in continuous real-time simulation and near-real-time (requires some response time) digital states. Other functions trigger, program, and hibernate (memory) based on events. Hard-wired logic can be used for high-volume, low-power applications (<200W), which typically operate at higher frequencies (200kHz to 2MHz) and near analog control speeds. This embodies the most rugged construction, does not require a large degree of programming by the customer, and can even be completely dispensed with (pin programming, or image user interface via I2C); and it can speed up the time to market. Joining NVM enables greater flexibility in integrated circuit design, but adds inspection and validation.

Hybrid logic can be formed if an analog controller is used with a digital interface that supports I2C communication and sometimes supports VID control. It shares the same space as the hard-wired structure, but the flexibility is lower and the cost is higher. Both are mainly used in the field of DC-DC. Both mC, DSP, and DCP use coding (assembly language or C) to achieve greater flexibility and speed, but at a higher cost and take longer to get to market. However, the increase in flexibility makes the circuit structure more complicated, so the cost of inspection and verification procedures will be higher.

Silicon process

The choice of technology to implement these types of logic is generally driven by cost; and as lower submicron technology (0.15/0.18mm) becomes more affordable, digital technology is undoubtedly more dominant and therefore faster. The transition from analog to digital technology. At some point, “showing more features at a lower cost” will become a new value, replacing “showing more features at the same cost”. In the 0.25mm range, the cost of analog and digital structures has long been the same, but with the cost of chips in the 0.18mm range, the cost of research and development has more than doubled. (See Figure 1, source ISSCC 2007 / SESSION 1 / PLENARY / 1.1)