PCB configuration determines the success of power supply design.
High switching frequency, causes EMI and is difficult to lower
Useful for EMI-compliant packaging products in addition to filters and shields


It's no exaggeration to say that PCB layout determines the success of a power supply design, as it determines electromagnetic interference (EMI) and thermal performance. Switching power supply layout is often overlooked until quite late in the design process. Therefore, utilizing proven EMI mitigation measures can ensure a stable power supply.

On the 26th, Analog World discussed the recent hot topic of EMI reduction in the automotive electronics industry and its solutions in an e4ds EE webinar. Tony Armstrong, Director of Power Products Marketing at Analog Devices (ADI), presented a method for designing products that meet the CISPR (International Electromagnetic Interference) standard, an international standard for electromagnetic interference (EMI) in electronic products.

EMI originates from high di/dt loops. High di/dt loops carry high AC currents on the power and load lines. Therefore, AC current input and output capacitors must be analyzed. After analysis, the high di/dt loop area should be eliminated or zero-impedance capacitors should be used. The optimal compromise between the two methods must be found by the developers themselves.

In power circuits, high-frequency noise is primarily caused by switching transitions coupled through parasitic resistance, inductors, and capacitors. How can we reduce high-frequency switching noise? A traditional method is to delay the MOSFET switch edges.

Slowing down the internal switch driver or adding an external switch driver is one option. However, this approach can increase switching losses and lower converter efficiency, especially when the switcher operates at a high switching frequency, such as 2 MHz.

High switching frequencies allow for the use of smaller inductors and capacitors, and they also offer the advantage of blocking AM radio band noise in vehicles. Therefore, they cannot be arbitrarily lowered. While adding filters or shielding can be considered as an alternative to adjusting the switching frequency, this increases component costs and circuit price.

Alternatively, consider adding spread-spectrum frequency modulation. By adopting components with high efficiency, high switching frequency, and low EMI characteristics from the outset, PCB power circuit design can be made easier, eliminating the need for the aforementioned trade-offs.

Director Armstrong highlighted the unique features of the ADI Silent Switcher® LT8610 and LT8614 step-down products, which eliminate the need for switch edge delays. These products utilize patented ADI technology during the packaging process to cancel out input noise, making them ideal for frequency-constrained environments such as automotive applications.