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电源模块提供许多优点。具有集成电感器的版本可以简化设计，减少整体大小，并帮助确保符合EMI标准。他们让您利用模块制造商在系统架构，组件选择，资格和采购中的专业知识，并帮助削减设计时间并降低PCB房地产要求。此外，在使用模块时，您不需要花时间确定您选择的电感器和其他无源元件是否能够承受扩展的温度范围或在高频下重复施加高电压。
但是，有效的选择和应用功率模块确实需要对几个关键概念的基本了解，包括EMI compliance, high-temperature storage (HTS) test, and inductor withstand voltage。HTS测试是一种确保电力模块可靠性的方法，特别是那些具有粉末铁芯的电感器的方法。这种电感器可以体验热老化，最有可能在高电压和开关频率下发生劣化。
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德州仪器公司’ standard HTS test takes six weeks, with the device under test (DUT) baked at 150°C. Once per week, the DUTs are removed from the temperature chamber, the inductance is measured, and then they’re returned to the chamber until the entire test completes.
Also key to reliability is inductor withstand voltage—the maximum instantaneous voltage that can be applied to an inductor’s terminals without causing dielectric breakdown. Because many inductor vendors don’t publish their inductor’s withstand voltage, TI uses an impulse tester to perform component-level characterization of all inductors it uses in its power modules.
此外，像TI的TPSM41625这样的电源模块具有EMI优化的内部布局，使您能够满足最严格的应用程序标准，包括医学成像和视频广播。电源模块还允许设计人员简化被动组件的资格和采购，因为许多所需的高质量组件都集成在模块本身内。
By opting for a module such as the TPSM5D1806, for example, you would end up using as many as 14 fewer components than if you had chosen the module’s converter counterpart, the TPS541620. That means 14 fewer passives to go looking for and qualify.
EMI Compliance for Your Design
尽管电源模块的内部EMI优化，you will still need to add some passive components to tailor the module to your specific application as well as ensure that the completed design meets relevant EMI standards. This includes the Comité International Spécial des Perturbations Radioélectriques’ CISPR 25 for automotive electrical applications and CISPR 22 for information-technology equipment. A key means of limiting EMI is to create good layouts that reduce the area of current loops.
An intentionally bad layout helps illustrate the drawbacks of large current loops.Figure 1shows a modified evaluation module (EVM) for the LMR23630 SIMPLE SWITCHER converter. Whereas the circuit’s two input capacitors should be as close as possible to the converter’s input pins, the modification deliberately relocates them about 2.5 cm from the input pins to simulate a bad layout.
Figure 2shows the results from the layout. The blue curve represents the properly laid out board, for which EMI remains within acceptable CISPR 22 limits. The red line represents the bad layout, for which EMI exceeds the relevant limits.
In addition to keeping the input capacitors close to the converter, you can help curtail EMI issues by keeping traces or cuttings in the ground plane to a minimum and protecting noise-sensitive nodes. For example, keep the trace from your circuit’s resistor divider to the converter’s feedback (FB) pin as short as possible(Fig. 3)。这里的长痕迹可以将电磁干扰耦合到FB引脚中，使EMI问题恶化并可能使您的设计不稳定。
电源模块有助于简化EMI缓解。基于转换器的设计与基于电力模块的设计的比较说明了后者的益处。基于转换器的设计使用TI LMR23630转换器，而基于电源模块的设计利用TI LMZM3603模块，该模块包含LMR23630以及电感器和其他无源元件。
As was the case for theFigure 1example, the EVMs for both designs have been modified to simulate a poor layout. For the converter-based design, the input capacitors have been moved 2.5 cm from the converter’s input pins; in the power-module-based design, the input capacitors have been moved 3.5 cm from the input pins.
如图所示Figure 4的EMI converter-basedEVM exceeds allowable CISPR levels. The power-module-based design is more forgiving of the suboptimal layout, and EMI remains within CISPR limits.
Beyond BOM Costs
传统上，模块比采用离散电感器的转换器更昂贵，但由于过程和材料的进步，这变化了。Indeed, the cost of the TLVM13630, a 3- to 36-V input, 1- to 6-V output, 3-A step-down power module, is about 75% lower than a similarly rated module introduced in 2010.
Consider as an example a 24-V input, 5-V output, 10-W design based on the TLVM13630. Compared with the similarly rated LM60430D buck converter, the TLVM13630 is about $1 higher in cost, and the complete BOM cost for the TLVM13630-based design is about 5% higher than for the LM60430D-based design.
然而，重要的是要超越BOM成本并考虑PCB成本和设计时间。TLVM13630比LM60430D小约30％，需要更少的外部组件，从而节省PCB房地产，降低布局复杂性，限制通孔的数量，并最大限度地减少EMI的潜在来源。虽然设计时间可以各不相同，但模块可以将设计时间缩短几乎一半。
结论
By choosing a power module that’s fully characterized for electrical, thermal, and EMI performance, you can eliminate the need for inductor selection, qualification, and sourcing. In addition, TI offers the resources you need for a successful design, including characterization data, WEBENCH simulations, and SIMPLIS or Spice models. These tools give you a head start in attaining the performance you need for your most stringent power-module use cases.
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