Digital power or digitally controlled power has several different meanings.
The simplest definition is the control of a switching regulator via a digital interface. This may include control of output voltage, switching frequency, or sequencing of multiple channels via I2C or a similar digital bus. Margining, power-up and power-down sequencing, etc. can all be controlled by one or more digital signals. In fact, many power management integrated circuits on the market today work in this way: controlling analog switching regulators via a digital interface. The
second is to add so-called digital telemetry to the previous definition. In this case, additional control functions are provided to monitor the status of the switching power supply, such as temperature, output current, input current, input voltage, output voltage, etc., and report them to the host on demand or periodically. Other information such as ID tags, fault status information, and even time-stamped events can also be stored in on-chip non-volatile memory and reported at a future time. High-end systems with a large number of digital integrated circuits are the target market for this type of digital power supply, while lower-cost consumer products may not need such information.
The third and most ambitious meaning of digital power is to completely replace all analog circuitry in the switching regulator with digital circuitry. This is said to make the switching regulator easier to design, configure, stabilize, adjust, and sell. Further reasoning is that by writing a few simple lines of code, a core digital power IC can be configured as a boost regulator, buck regulator, inverting, SEPIC, flyback, or forward converter. It is this meaning of digital power that is the most difficult to understand, because power is fundamentally analog. Even digital switching regulators that replace error amplifiers and pulse width modulators with ADCs and DSPs still require voltage references, current sensing circuits, and switch or FET drivers. In addition, inductors or transformers and capacitors are indispensable in implementing digital power.
2. The difference between digital power supply and analog power supply
The difference between digital power supply and analog power supply is mainly concentrated in the control and communication part. In applications where it is easy to use and there are not many requirements for parameter changes, analog power supply products have more advantages because the targeted application can be achieved through hardware solidification, while digital power supply has advantages in complex high-performance system applications with more controllable factors, faster real-time response speed, and multiple analog system power management.
In addition, in complex multi-system business, compared with analog power supply, digital power supply is realized through software programming in many aspects. Its scalability and reusability enable users to easily change working parameters and optimize the power supply system. Through real-time overcurrent protection and management, it can also reduce the number of peripheral devices.
Digital power supply is controlled by DSP and MCU. Relatively speaking, the power supply controlled by DSP adopts digital filtering, which can better meet complex power supply requirements, faster real-time response speed, and better power supply voltage regulation performance than the power supply controlled by MCU.
What are the advantages of digital power supply? First of all, it is programmable. For example, all functions such as communication, detection, and telemetry can be realized by software programming. In addition, digital power supply has high performance and high reliability and is very flexible.
3. Development of digital power supply
Digital power supply is a new technology. At present, its development is difficult to promote due to some misunderstandings:
1. The cost of digital power supply is frighteningly high.
In the past, when people mentioned "digital", they thought that the cost was higher than that of traditional analog solutions. Compared with other advantages of digital solutions, such as reduced size, flexibility and adaptability, enhanced testability, diagnostic functions and expanded functions, high cost is a major negative factor. However, compared with analog feedback loops manufactured using proprietary technologies that occupy larger space, it costs less to implement digital feedback loops using CMOS technology available on the market. In addition, the overall cost of solutions using true digital power supplies is much lower than other existing solutions.
2. Digital power supplies are much more complex
There is a perception that power supply designers are born analog designers who do not want to deal with the complexity of programming. Proponents of digital power management argue that not only are we not paying enough attention to designers who seek innovation (who are not threatened by the rise of digital power), but that programming does not actually mean writing code, but rather dealing with wizard-driven graphical user interfaces (GUIs) to gain a variety of system-level benefits, including:
(1) Simplified system-level temperature management through real-time telemetry technology;
(2) Real-time telemetry technology improves the reliability of predicting failures before they occur;
(3) Improve manufacturability through fully automated inspection and variable resistor fine-tuning during the final module or motherboard test phase.
In fact, the slow acceptance of digital power supplies is due to customers' belief that digital technology is unproven, complex, and expensive. This is not surprising, as the industry encountered a similar situation in the late 1970s: when power supplies changed from linear to switching, switching was also initially considered expensive and unreliable (noisy output). However, once customers recognized the advantages of switching power supplies (higher performance and smaller size) and learned how to implement the new switching power supply technology, linear power supplies were quickly eliminated. A few years later, as customers became familiar with its advantages, more providers and solutions appeared on the market, and they saw that they could achieve better results than analog solutions without additional cost, digital technology will undergo a similar transformation.
From the current situation, major companies such as iWatt, TI Texas Instruments, and Linear Technology have launched their own digital power ICs, which shows that the industry is optimistic about the prospects of digital power supplies. According to reports from iSuppli and Lehman Brothers, the entire digital power market will generate revenue of approximately US$168 million in 2006 and will soon become a very important part of the power market; the industry estimates that the compound annual growth rate (CAGR) will exceed 100% in the next few years.
At present, the leading digital power IC developers include Texas Instruments, Linear Technology, Integrated Power and other large companies. The following uses Texas Instruments' UCD7K, UCD8K and UCD9K series digital power ICs as examples to introduce the main features of digital power ICs.
1. UCD7K digital power driver
Texas Instruments' UCD7000 series ICs are mainly used in digital power supplies or in situations where fast local current limiting protection is required. They are compatible with standard 3.3V DSP microcontroller I/O ports. UCD7201 is one of the series, and its functional block diagram is shown in Figure 1.
Figure 1. Block diagram of Texas Instruments digital power IC UCD7201
UCD7201 can be connected to digital power controllers such as UCD9110 and UCD9501 in a two-terminal topology. Programmable threshold, with digital output current limit flag that can be monitored by the main controller. High impedance digital input terminal, can input 3.3V logic level signal with frequency up to 2MHz, and there is a Schmitt comparator inside the pin to prevent external noise interference. There is a current limit flag pin. The current limit threshold setting port can set the threshold to any value between 0.25V and 1.0V. When it is open, the threshold default value is 0.5V. The pin configuration position of the above ports varies depending on the component package. The IC can also provide power to the controller. The typical application circuit of UCD7201 is shown in Figure 2.
Figure 2. UCD7201 typical application (push-pull converter)
2. UCD8K series digital power controller
UCD8620 is a digitally controlled push-pull analog PWM controller, one of the UCD8K series products. Its internal structure is shown in Figure 3. The main features of UCD8620 include: using voltage mode or peak current mode control to provide flexible control methods; using marked programmable overcurrent limit to provide fault protection and flexible overload protection; accepting clock input from the digital controller, and its digitally controlled switching frequency has a maximum duty cycle; with a 110V high-voltage circuit, it can directly use a simplified 48V circuit; and the digital controller is powered by an on-chip 3.3V, 10mA linear regulator. Figures 4 and 5 show its typical applications in telecom half-bridge input converters and telecom push-pull input converters, respectively.
Figure 3: UCD8620 internal structure
Figure 4. UCD8620 Typical Application: Telecom Half-Bridge Input Converter
Figure 5. UCD8620
Typical Application: Telecom Push-Pull Input Converter
3. UCD9K High-Resolution Digital Controller
UCD9501 is the first product of UCD9K series high-resolution digital controller. It contains a 100MHz, 32-bit Harvard structure DSP core, a clock and timing control module, a 12-bit, 6.25MS/s sampling rate ADC; external digital I/O, including PWM output and memory. The internal structure of UCD9501 is shown in Figure 6. Figure 7 is a digital power reference design based on UCD9501 or F2801 DSP.
Figure 6: UCD9501 internal structure
Figure 7. AC/DC rectifier reference design
As IC manufacturers continue to launch new models and digital power IC products with better performance and users gain a deeper understanding of digital power, digital power will become popular. Digital power products with flexible design methods and high reliability will bring convenience to people's lives.
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