Buck调节器是以其效率而闻名的多功能组件。但是，将它们部署在必须满足电磁干扰（EMI）要求的产品中，例如ComitéInternationalSpécialDestestturtationsRotoélectriques（CISPR）可能会带来挑战。
驱动监管机构高性能的高开关频率会加剧排放。幸运的是，具有集成电容器的监管机构并采用传谱转换技术，可以轻松地帮助您满足EMI要求。
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集成电容器
图1显示了具有输入电容的简化降压器（C在）代表低频和高频电容器。当高频电容器电流环中的高瞬时晶体管（MOSFET）Q1打开时，高瞬态电流（DI/DT）流动时，高频电流电流电流电流环中的高瞬态电流（DI/DT）时。
1.电容器c在and CBOOT当高侧MOSFET Q1开关时，会体验高瞬态电流。
限制EMI的关键因素是使此类环的区域保持高DI/DT的高度，同时还将高压电压（DV/DT）节点的表面积最小化。为了帮助这两个因素，您应该将输入电容器尽可能靠近降压器IC找到。
Layout constraints, however, often preclude optimal capacitor placement. To overcome layout limitations, you can use buck regulators such as Texas Instruments’ LMQ66430-Q1 and LMQ61460-Q1, which deliver 3 A at 36 V and 6 A at 36 V, respectively, and are both qualified to the AEC-Q100 quality standard for automotive applications.
Each buck regulator integrates high-frequency input capacitors inside the regulator package. This integration reduces the need for external capacitors and results in the smallest possible input-capacitor current-loop area, thereby minimizing parasitic inductance in the loop and reducing the amount of energy emitted.
此外，两者都提供增强的包装，以最大程度地减少开关节点振铃。例如，LMQ61460-Q1出现在Ti的Hotrod Flip-chip-on-leadFrame软件包中，该软件包没有内部粘结线，从而消除了重要的输入环电感源。
此外，请注意启动电容器（CBOOT） 在图1。它的工作是在Q1打开时向高端门驱动器提供费用。（Q1关闭时，内部电路会刷新该电容器的电荷。）CBOOTestablishes another high-di/dt current loop whose area should be minimized. The TI LMQ66430-Q1 integrates this capacitor inside its package, thus limiting the area of the high-di/dt current loop and associated high-dv/dt voltage node while also reducing the need for external components.
驱动率控制
最大程度地减少质调节器设计中的EMI的一种常见方法是利用SLEW速率控制。例如，使用LMQ61460-Q1，例如外部引导电阻（RBOOT）控制转机期间高方面FET驱动器的强度。R的值100ΩBOOT导致大约2.7-ns开关节点上升时间，这实际上消除了过冲。
Although slew-rate control does reduce emissions, it’s at the expense of lower efficiency.By utilizing a buck regulator with integrated input capacitors, though, you might be able to achieve the desired EMI performance without resorting to slew-rate control，如示例所示图2。
2. The plot on the left represents a buck regulator with no integrated capacitors but using maximum slew-rate control, while the plot on the right shows a device having integrated capacitors but no slew-rate control.
左侧的情节图2represents a buck regulator with no integrated capacitors but it uses maximum slew-rate control, while the plot on the right represents a device with integrated capacitors but has no slew-rate control. The device with integrated capacitors achieves a 4- to 5-dBmV improvement in emissions performance compared with the device with maximum slew-rate control. And the superior performance of the device with the integrated capacitors comes with no sacrifice in efficiency.
传谱技术
In addition to minimizing the areas of high-di/dt current loops and high-di/dt voltage nodes, you can take other steps to minimize EMI. A switching device like a buck regulator generates EMI at its switching frequency and at the harmonics of that frequency.
减轻此类EMI的一种方法是使用传谱技术来抖动开关频率。它可以使基本的基本变量融为一体，并将谐波融合到平滑的平均波形中，其值保持在相关的EMI标准设定的限制范围内。
常见的传播实现采用了三角形或伪和伪调制。三角调制在基本频率下效果很好，使您可以降低EMI滤波器的尺寸和成本，但在较高频率下的效果较低。此外，许多三角调制方案在4到15 kHz范围内具有三角波频率。如果耦合到附近的音频电路甚至以相同频率共振的陶瓷电路中耦合，则可以产生听觉音调。
另一方面，伪随机调制可能不会均匀地衰减基本，从而限制了过滤器的尺寸减小。但是，它在高频上保持其性能，并且不会表现出可听见的音调问题。
To get the benefits of both approaches while limiting the drawbacks, you can choose a switching regulator that employsTI的专有双随机传播频谱（DRSS）技术，例如LMQ66430-Q1。DRSS方法始于三角调制（图3，顶部）。然后，它随机划分三角波形的频率(Figure 3, middle)to address the audible tone issue, spreading the tone into white noise.
3.TI的drs技术始于三角模ulation, randomly dithers the triangle frequency, and adds pseudorandom modulation on top of the dithered-triangle modulation.
最后，为了解决三角调制的次优高频性能，Drss在抖动 - 三角形调制的顶部添加了伪和调制（图3，底部）。In addition to spreading the audible tone into white noise, DRSS goes a step further to actively reduce that noise.
Conclusion
High transient currents are major drivers of buck-regulator EMI, and minimizing the areas of high-di/dt current loops and high-dv/dt voltage nodes is critical. Integrating high-frequency capacitors inside the regulators minimizes those areas as much as possible to assist with meeting EMI compliance requirements.
Choosing a device with TI’s proprietary DRSS technology can further reduce unwanted emissions. Finally, buck regulators with integrated capacitors also help cut BOM count and reduce power-supply size.
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