MAX20021/MAX20022 PCB Layout Guidelines

introduce

Proper PCB layout is critical, especially in the design of high-frequency switching regulators (such as the MAX20021/MAX20022). An optimized PCB layout can provide clean outputs and simplify debugging during electromagnetic interference (EMI) testing. This article introduces some key areas for optimizing circuit layout to ensure the best performance.

General Layout Design Guidelines

1. Keep the loop area formed by the input capacitors (C5-C8), inductors (L1-L4), and output capacitors (C1-C4) to a minimum.

2. Place the VA output capacitor (C9) as close as possible to pin 26 (VA) and pin 24 (GND), with no vias between the capacitor and the pins. This pin is the analog power input of the IC, and any inductance generated on the lead will increase analog noise, thereby increasing the output jitter of LX[1:4].

3. Give priority to using the shortest possible routing.

Optimizing AC-DC current paths

To reduce electromagnetic radiation, the layout of passive components around the MAX20021/MAX20022 is critical. The path with a current step change is called the AC path, which appears at the moment of the switch on/off operation. After the switch is turned on/off (ON/OFF), the path through which the current flows is the DC path.

Communication Path

The MAX20021 synchronous rectification DC-DC converter has three passive components (C1, C5, L1) on the switching current path of each output. These three components have a significant impact on electromagnetic radiation and device performance. Figures 1 and 2 show the switching current path of OUT1 during the ON/OFF period; Figure 3 shows the difference between the two current paths with the maximum di/dt. The routing of C5 should be given priority, followed by the routing of L1 and C1.

Figure 1. Current path of OUT1 when PMOS is on.

Figure 2. Current path of OUT1 when DMOS is on.

Figure 3. OUT1 AC path differences

Spread Spectrum

If the improved wiring does not pass the user's radiation standard test, the MAX20021/MAX20022 products with clock spread can be customized. Compared with the standard version of the device, the spread spectrum device can reduce the noise in the FM band by 12dB. For the process of customizing the spread spectrum device, please refer to the relevant instructions in the device data sheet.

Example: Four-layer PCB design layout

Figures 4-7 are schematic diagrams of a four-layer board made according to the above wiring guidelines.

Figure 4. 4-layer board layout – top layer

Figure 5. Four-layer board layout – PGND layer

Figure 6. Four-layer board wiring – VSUP layer

Figure 7. Four-layer board wiring - bottom layer

in conclusion

Reasonable layout of the peripheral components of the switching regulator MAX20021/MAX20022 (Figure 8) can help reduce noise and electromagnetic radiation at the source, save valuable time in the project evaluation stage, and shorten the product development cycle.

Table 1. Components list

Figure 8. PCB layout schematic