How to improve the performance of automotive power supply through wiring technology

When using high frequency switching regulators, good automotive power PCB layout can provide a cleaner output and ease debugging in EMI testing. This article uses the MAX16903/MAX16904 switching regulator design as an example to describe how to wire it to achieve optimal performance and reduce emissions.

When using high frequency switching regulators, good automotive power PCB layout can provide a cleaner output and ease debugging in EMI testing. This article uses the MAX16903/MAX16904 switching regulator design as an example to describe how to wire it to achieve optimal performance and reduce emissions.

introduction

When using high-frequency switching regulators such as the MAX16903/MAX16904, good automotive power PCB layout can provide cleaner outputs and simplify debugging during electromagnetic interference (EMI) testing. This article uses the MAX16903/MAX16904 switching regulator design as an example to describe the layout principles for optimizing system performance.

General rules for wiring

Keep the loop area formed by input capacitor C3, Inductor L1, and output capacitor C2 at .

Place the BIAS output capacitor (C4) as close as possible to pins 13 (BIAS) and 14 (GND) without vias between the pins and the capacitor. This is the IC’s analog power input, any inductance on the negative wire will introduce noise into the BIAS power supply, increasing the jitter at the LX output.

Use the shortest possible leads.

Optimized AC-DC current path

To minimize electromagnetic radiation, the layout of the MAX16903/MAX16904 peripheral components is critical. The path of the current jump is called the AC path and occurs when the switch is ON/OFF. After the switch is turned ON/OFF, the current in the current path is the DC path.

communication path

The switching current path of the MAX16903 synchronous DC-DC converter requires three passive components (C2, C3, L1), which have a significant impact on electromagnetic radiation and device performance. Figures 1 and 2 show the current paths for the ON and OFF cycles; Figure 3 illustrates the difference between the two current paths where di/dt occurs. The routing of C3 should be given priority, followed by the routing of L1 and C2.

How to improve the performance of automotive power supply through wiring technology

 How to improve the performance of automotive power supply through wiring technology

Bootstrap AC Path

The MAX16903/MAX16904 DC-DC converters use a high-side DMOS transistor that requires a voltage higher than 5V on the LX pin (DMOS source). To generate this voltage, a bootstrap capacitor is required between the LX/BST pins (Figure 4). During the OFF period of the DMOS, the 5VBIAS regulator charges the bootstrap capacitor C1; the BIAS output also powers the error amplifier. Therefore, it is important to keep the BIAS as clean (low noise) as possible so as not to negatively affect the error amplifier, keep the inductance as small as possible between C4 and the MAX16903/MAX16904, C4 should be as close as possible to pins 14 (GND) and 13 (BIAS) placement, do not add vias.

How to improve the performance of automotive power supply through wiring technology

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