Introduction to Digital Power Module Design Techniques

　　More and more industrial and communication applications benefit from non-isolated DC/DC power module products, including reliability, volume, etc. These benefits help shorten the time to market of terminal products, and terminal companies no longer need to carry out complex power design and development. DC/DC power modules can enhance the portability of products and reduce product size. Standard power modules integrate passive devices, inductors, MOSFETs and controllers to provide a complete fully integrated solution, and use standard packaging, covering the full current and voltage range, at a reasonable price.

　　The power module combines most of the necessary components to provide a plug-and-play solution, replacing more than 40 different components. This integration simplifies and speeds up the design of the system, and it can also significantly reduce the circuit board area occupied by the power management part. In order to achieve the required voltage accuracy, these power modules are generally placed near the chip circuit that needs to be powered on the circuit board. However, as the complexity of the system increases, layout becomes more important in systems with higher current, lower voltage and higher frequency.

　　The most common non-isolated DC/DC power modules are single in-line packages (SIPs) and open-frame structures. They can obviously bring convenience to engineers and simplify system design. However, they are generally only suitable for designs with lower switching frequencies, such as 300kHz or lower. Furthermore, their power density is usually not optimized, especially compared with DC/DC chip-level modules.

　　When evaluating different power modules, engineers must compare the characteristics of various power modules for their specific applications, including the module's electrical, thermal performance, size, and reliability specifications to decide whether to use traditional modules or new high-density modules with optimal thermal resistance.

　　Chip-scale packaged DC/DC modules

　　The latest module is a fully encapsulated DC/DCPOL digital power module that combines all the advantages of digital power solutions using PMBus and a fully encapsulated approach. Using an internal digital controller, PMBus can be used to set various parameters to meet the needs of specific applications. Various parameters can be monitored and stored in on-board memory, and in the most advanced modules available, almost all discrete components are integrated into the module. Advantages include shortened time to market, simplified components on the printed circuit board, and enhanced long-term reliability. This fully encapsulated approach provides a larger heat sink pad at the bottom of the package to enhance heat dissipation capabilities, and the pins on the edge of the package also have ideal solder joint detection capabilities. This module can operate at 3.3V, 5V, and 12V bus input voltages, provide 0.54V~4V step-down outputs, have a single resistor setting, and an output current capability of up to 12A. The fully encapsulated digital power module can provide a variety of combinations to meet a wide range of application requirements.

　　One of the main benefits of fully packaged digital power modules is the increase in power density, which is achieved by improving the heat dissipation of the package. Power density and thermal resistance go hand in hand, especially for higher power solutions above 25W. For decades, the semiconductor industry has been in a race to improve power density/integration, the most basic reason is that systems are becoming more powerful and require more components, but the size of the entire system must be reduced to remain competitive. Therefore, the size of the components/solutions has become the key to this trend, which means that customers can fit more things on a smaller board and more powerful/larger power processors, such as server applications or automatic test equipment. Obviously, the lower the thermal resistance, the higher the power density can be, and some power module products cannot achieve higher power due to the problem of package thermal resistance. Furthermore, the better the thermal efficiency of the solution, the less users need to worry about or design restrictions, such as having to ensure that there is sufficient airflow or adding heat sinks. In the enhanced QFN package, a larger thermal pad on the bottom of the package body, together with the enhanced package overmold material, acts as a heat sink, resulting in optimal thermal performance of the fully encapsulated power module (Figure 1).

　　Figure 1. Advantages of heat dissipation in a fully encapsulated module.

　　The extremely low thermal resistance is demonstrated by the junction-to-ambient resistance of 11.5C/W and the junction-to-case resistance of 2.2C/W. This performance allows for a higher power solution in a smaller form factor. Since the core-to-case thermal resistance is so low, most of the heat is dissipated through the bottom of the package. Compared to open-frame modules, this power module can operate at full load over the full industrial temperature range without any airflow. The heat dissipation capability of the module package has a huge impact on whether higher power density can be achieved than traditional open-frame modules or discrete power solutions, and makes fully packaged modules the best choice to replace other modules.

　　Fully encapsulated module solutions have higher reliability and manufacturability. For example, since all components are fully encapsulated, they can be better electrically isolated from the outside world; there are fewer solder joints, so the problem of solder joint damage over time is also reduced; there is less chance of package cracking due to pressure in specific applications. In addition, compared with non-planar open architecture solutions, fully encapsulated is more suitable for traditional automatic placement machine production.

　　In addition to being fully encapsulated, the module also has the advantage of being able to configure and monitor the power system using PMBus and I2C interfaces. The best way to leverage these benefits is through a simple graphical user interface (GUI) that allows designers to adjust various operating parameters such as soft-start time, output voltage margining, voltage tracking, and PowerGood signals. This approach eliminates the need for external circuitry and is flexible enough to meet current and future design needs.

　　Whether in the development stage or in the application stage, various parameters of the system can be monitored. For example, the output state, voltage and current can be monitored and stored in non-volatile memory, plus the date, and can be read externally when needed. Such intelligent power supply makes the performance of the entire system more superior. At the same time, system monitoring ensures long-term reliability. The monitoring data is saved and simplifies the failure analysis process. At the same time, once the digital power module completes the internal configuration in a specific application, this configuration document can be read through the configuration program and copied to other identical products.

　　Intersil's ZL9101MIRZ is one of the latest examples of DC/DC fully encapsulated power modules. It combines the next generation of packaging and digital power management technology, greatly reducing external components and simplifying the design of complex POL power supplies. It can provide better reliability than traditional open architecture modules or discrete solutions, and greatly shorten the design cycle and time to market. It uses the graphical interface PowerNavigator software for design and monitoring, which is easier to operate.

　　In some cases, fully encapsulated modules can achieve four times the power density of ordinary modules. For example, comparing the ZL9101MIRZ with open-frame modules on the market, the ZL9101M has a power density of 38W/cm3 (common modules are 8.6W/cm3), and its footprint on the circuit board is also very small, 2.2cm2 versus 3cm2 for ordinary modules, a difference of about 30 percentage points, which is very important when the board space is extremely small.

　　In general, packaged digital power module technology can combine next-generation packaging technology with easy-to-use digital power technology, simplify the design of POL power supply with minimal external components, provide higher reliability than traditional open-framework power modules or discrete solutions, and significantly shorten the design cycle.