Expert technical article: Dull vs. smart: When does it make sense to add intelligence to your power supply?

Power conversion applications are everywhere. From portable devices that use boost converters to regulate the voltage of a dwindling coin cell battery to cellular base stations that do a lot of redundant AC-DC conversion: everything needs power. There is a lot of talk in the industry about digital power; moving power conversion to software, for example, and eventually replacing all of our power hardware with software. The reality is much more complex and far less dynamic. Most power conversion is (and always will be) implemented in dedicated hardware. However, as digital signal processors (DSPs) and digital configuration controllers become more powerful, more options and power conversion capabilities are available to savvy designers, not to mention designers who are not afraid to take a crack at firmware compilers. The big question is timing; when is it worthwhile to add firmware to the design process, and when is it better to use traditional analog power conversion? The answer is as fluid as the power conversion it covers. There are four main factors driving investment in digital power conversion today: reporting, reliability, dynamic load management, and total cost of ownership.

Data reporting is one of the key benefits of digital power. In many systems, it is beneficial to know the processor load current, battery voltage, or power level. This information can be used to throttle fan speeds, manage system cooling, or report status to the user. In the case of a generating or sourcing application, this capability can report local power generation to a central system, or report power required in the case of power consumption - both of which can make the overall system more efficient. Today, almost all battery backup or battery power supplies use some form of fuel gauging. In high-performance computing applications, users may want to see that the system voltage is just enough to overclock a microprocessor, or a data center may just want to monitor where its (real) power budget is being spent. Accurate voltage reporting is common, but accurate current or accurate power reporting is more difficult. The latter two require good measurement circuits, usually built around an analog-to-digital converter somewhere in the system. In addition, whether it is I2C(TM), SMBus(TM), PMBus(TM), Smart Battery, SPI, or any other method (standard or proprietary), the measurement data needs to be reported. This measurement and reporting requires digital circuitry, but does not actually require a digital control loop, so it can be implemented separately, using a supervisory circuit (perhaps using a PIC12F18xx family microcontroller) to monitor an analog voltage converter. The voltage conversion can also be done in a Core Independent Peripheral (CIP) on a PIC® MCU, or using monolithic analog control built into an MCU (such as the MCP19xxx family of devices). These approaches all allow for digital reporting and do not require a digital control loop, which generally speeds up system design. With such a system, it is easy to add some level of digital circuitry for reporting and can be built around an analog power supply.

Figure 1: Digital management of analog power supplies This approach is easier to implement than a true digital control loop, while still providing many of the advantages of digital power. When using modern controllers, you will find these blocks integrated into a single IC, such as the MCP19119.

报告可提高系统的可靠性。硬件现在可以监视异常行为，并进行通告，可在导致硬件故障之前检测到问题。这样一来，便可延长数据中心等高可靠性系统的正常运行时间。此外，还可使用数字控制回路进一步提高可靠性。模拟控制回路的补偿取决于随时间发生偏移的无源模拟组件。数字计算始终是相同的。不过，更大的优势在于能够处理故障和错误。与纯模拟控制电路相比，智能固件能够采取更多措施来减轻或标记有问题的情况。更重要的是，它可以响应这些错误。这可能意味着切换到冗余电源，或通知系统操作员设备需要修理。在系统层面上，这可以显著提高可靠性。

When using a digital communications interface, the application is also able to receive digital commands. This allows for more sophisticated load management. Adaptive voltage scaling, voltage margining, or even just complex loads require the ability to dynamically adjust the power supply’s operation. These can be accomplished through standardized commands such as the PMBusä standard or the Smart Battery Protocol; or through proprietary commands over an I2C or SPI interface. Operational changes can also be made based on environmental measurements such as ambient temperature, input voltage, or load power changes—without any external communications. If a purely analog supply detects a brownout and locks out the processor power, a digital controller might reduce the output voltage, signal the processor to slow down, and then slow down processing until the input is restored (a slow response is better than no response). The system can also adjust the operating frequency in real time, improving efficiency under various load conditions while still maintaining the benefits of fixed-frequency operation. Similar to data reporting, these are typical applications for digital circuits, but (depending on the exact performance changes required) they do not always require digital power control. For example, Microchip’s MIC24045 analog power controller can be managed using an I2C interface. Among other things, the device can dynamically adjust the output voltage or current limit to accommodate changing requirements.

The final decision usually comes down to whether it can reduce the total cost of ownership. If the reduced total cost of ownership due to the advantages of digital power is greater than the increased system cost (in terms of development time and hardware), then digital power is the clear winner. As digital control becomes more common, better design tools make digital control design easier, and digital control is becoming cheaper and easier. Microchip's software support suite includes the Microchip Code Configurator graphical interface for configuring MCUs, and digital power control tools for generating code to simulate pole-zero placement that can easily close the loop. This reduces the investment required to create digital power control, and digital solutions play a key role in more and more applications. At the same time, as digital signal processors increase in speed, transient response and operational changes are also getting faster. By continuously adjusting the power supply operation to the current load conditions and temperature, digital power can maintain a high average efficiency over a wide range of load conditions. This efficiency advantage directly translates into profits in power generation applications (such as solar inverters), and can also reduce overhead costs in power consumption applications (such as data centers or base stations).

Figure 2: Comparison of analog and digital control loop implementations (block diagram level). If the power supply meets the application requirements, the user will never know the difference.

Whether the control loop is analog or digital, as long as it works properly, the user will not know the difference. If the application advantage does not exist, it may not make sense to use a digital control loop or a digital controller. In these cases, there are many analog power solutions that can meet the application requirements of smaller circuits and easier implementation. Power modules (integrated packages containing silicon controllers, power MOSFETs and magnetic components) are providing exciting integrated options that almost completely eliminate the power supply design work. For example, the MIC45404 module can perform 12V to 3.3V conversion with an output current of up to 5A using only two external capacitors. Compared with digital power solutions, this is a very accurate power conversion, and the only design work required is the board layout. In many applications, this simple approach will help products to be put into market faster while still providing effective DC-DC conversion.

With great power comes great responsibility. Digital control loops, hybrid PWM controllers with digital interfaces, or CIP-based MCU solutions all enable more configurations than their analog predecessors. This provides greater design flexibility, but it requires system designers to spend time writing firmware to configure the corresponding additional parameters. In many cases, the results are worth it - but analog control will always be the mainstay of power conversion.

Note: The Microchip name and logo, the Microchip logo and PIC are registered trademarks of Microchip Technology in the U.S. and other countries. All other trademarks mentioned herein are property of their respective companies.