From the smallest Internet of Things (IoT) home automation sensors to the largest industrial machines, every circuit requires power. Power supply design requires a lot of work, and the power circuit takes up board space. But in many applications, end users don't realize the benefits of a better power supply. Design work can be said to be completely unrecognized.
The power module is a tested, complete power supply that combines the advantages of low noise, high efficiency, and compact layout, so in these cases, power modules can be used to eliminate design effort. A power module is a separate component placed in a package on a printed circuit board (PCB) that contains the entire switching power supply (including inductors). Pulse width modulation (PWM) controllers, MOSFET drivers, power MOSFETs, feedback networks, and magnetic components are all contained in the same package.
Figure 1: Advances in Power Module Packaging Technology Simplify and Accelerate New Product Design
The main design challenges in power supplies are stability, transient response, efficiency, EMI, and layout. With discrete implementations of on-board power solutions, these features need to be tested for each power supply, even when the design is re-used for new layouts on new boards. Even in cautious simulations or previously prototyped circuits, actual layouts can introduce stability issues, electromagnetic radiation, unexpected transient behavior, or unexpected efficiency results. This may add unnecessary design iterations to the project and may delay the release of the entire product. One of the main advantages of power modules is to eliminate these risks. Considering performance, the power supply layout is primarily within the power module. The inductor, controller and power transistors are all packaged together with fixed, tested and verified internal connections. Efficiency, transient performance, stability, and EMI are all listed in the data sheet. Line and load transient response; enabling and disabling transient response; even waveforms that are initiated to short-circuit or fault conditions can be found in the documentation. This provides known good performance and completes the design with minimal effort and minimal risk. There is no way to achieve an onboard DC/DC conversion that is simpler than a power module.
The second advantage of the power module is the circuit size. The signal wiring inside the module is more compact than on the PCB. As a result, modules are generally superior in power density to similar products that are implemented discretely. In some applications, this produces a difference from the target shape. End users expect smaller IoT platforms, wearable electronics and solid state drive solutions to be small. This small size sometimes introduces other problems associated with device temperature ratings. Many power modules are only suitable for operation at full load current ratings under temporary or transient load conditions and need to be derated to lower currents during steady state operation. Part of the reason is the natural result of system thermodynamics. Therefore, this requires a better thermal design to handle the same amount of heat in a smaller space. For example, Microchip uses thermally efficient copper leadframe packaging technology to minimize thermal resistance compared to PCB-based or multi-step packaging methods. In this way, the Microchip module can operate at full load current rating in most thermal environments and at higher ambient temperatures.
The power module has very low radiation. The tightly packaged nature minimizes the distance between components on the phase node and places the power transistor gate very close to the power driver. In discrete PCB layouts where power is implemented, the best practice is to minimize the length of these traces so that there is no hope of EMI. However, this will not be known until the finished product is tested. For power modules, these connections are internal to the module and have significantly shorter trace lengths than if each silicon chip was individually packaged and connected together on the PCB. In addition, this module can be tested separately for EMI, regardless of the target circuit in which the module is designed. The Microchip module typically meets the CISPR-22 Class B rating criteria given in the data sheet, so there is no uncertainty in the performance of the final circuit. This not only eliminates the risk of accidental EMI problems; but in general, the total EMI is much lower than if the integrated power solution was not used.
Modules also achieve a degree of flexibility. Even if the power supply is complete and tested, the selected critical operating parameters can be adjusted via external components or routing. For example, with Microchip's MIC45404 power module, the output voltage, current limit, and switching frequency can be selected through trace routing on the PCB. The internal comparator checks the external pins to determine if these inputs are grounded, floating, or connected to the supply input voltage (using the PCB traces on the board). Based on these connections, the controller can select the output voltage (nine options), the switching frequency (three options), and the output current limit (three options) without external passive components (or their tolerances). In this way, one module can meet multiple power requirements in one or more designs without having to define and reserve multiple part numbers.
There are several ways to cause a bad power supply, but using a power module is not one of them. The module eliminates the need for inductors and minimizes PCB layout. The input, output, and compensation networks can all be calculated using the direct formulas in the data sheet to meet application requirements based on stability and transient response requirements. This allows the system architect to freely spend more time in other parts of the system design, adding value to the final product or shortening the time to market. Small, fast, efficient, and easy-to-use power modules represent a new level of power component integration—a technology that ensures power is removed from the system design process.