Integrated input bypass capacitor

As we described earlier, a large input power loop results in higher emissions at high-frequency bands because of increased switch-node ringing. Integrating high-frequency input decoupling capacitors inside the device package helps minimize the input loop parasitic and thus reduces EMI. This technique is used in the LMQ62440-Q1, a step-down converter, as shown in Figure 20 on the following page. Beyond reducing the input power-loop inductance, the package integration of the input high-frequency capacitors also helps make the solution more immune to changes in the board layout of the end system.

bands because of increased switch-node ringing. Integrating high-frequency input decoupling capacitors inside the device package helps minimize the input loop parasitic and thus reduces EMI. This technique is used in the LMQ62440-Q1, a step-down converter, as shown in Figure 21. Beyond reducing the input power-loop inductance, the package integration of the input high-frequency capacitors also helps make the solution more immune to changes in the board layout of the end system.

Figure 22 compares the radiated EMI — identical conditions on identical boards — of the LMQ62440-Q1, with and without the bypass capacitors integrated. The results show a 9-dB reduction in emission in the most stringent TV band (200 to 230 MHz), which helps the system remain under EMI limits set by industry standards without the need for additional components on the board.