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LM60440, LM60430

SNVSBN5A – FEBRUARY 2020 – REVISED JUNE 2020

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Copyright © 2020, Texas Instruments Incorporated

11 Layout

11.1 Layout Guidelines

The PCB layout of any DC/DC converter is critical to the optimal performance of the design. Bad PCB layout can

disrupt the operation of an otherwise good schematic design. Even if the converter regulates correctly, bad PCB

layout can mean the difference between a robust design and one that cannot be mass produced. Furthermore,

the EMI performance of the regulator is dependent on the PCB layout, to a great extent. In a buck converter, the

most critical PCB feature is the loop formed by the input capacitor or input capacitors, and power ground, as

shown in Figure 21. This loop carries large transient currents that can cause large transient voltages when

reacting with the trace inductance. These unwanted transient voltages will disrupt the proper operation of the

converter. Because of this, the traces in this loop must be wide and short, and the loop area as small as possible

to reduce the parasitic inductance.

1. Place the input capacitor or capacitors as close as possible to the VIN and GND terminals. VIN and

GND pins are adjacent, simplifying the input capacitor placement. With the WQFN package there are two

VIN/PGND pairs on either side of the package. This provides for a symmetrical layout and helps minimize

switching noise and EMI generation. A wide VIN plane must be used on a lower layer to connect both of the

VIN pairs together to the input supply; see Figure 22.

2. Place bypass capacitor for VCC close to the VCC pin. This capacitor must be placed close to the device

and routed with short, wide traces to the VCC and GND pins.

BOOT and SW pins.

if used, physically close to the device. The connections to FB and GND must be short and close to those

routed near any noise source (such as the SW node) that can capacitively couple into the feedback path of

the regulator.

5. Use at least one ground plane in one of the middle layers. This plane acts as a noise shield and also act

as a heat dissipation path.

6. Provide wide paths for VIN, VOUT, and GND. Making these paths as wide and direct as possible reduces

any voltage drops on the input or output paths of the converter and maximizes efficiency.

7. Provide enough PCB area for proper heat sinking. As stated in the Maximum Ambient Temperature

current and ambient temperature. Make the top and bottom PCB layers with two-ounce copper; and no less

than one ounce. If the PCB design uses multiple copper layers (recommended), thermal vias can also be

connected to the inner layer heat-spreading ground planes.

8. Keep switch area small. Keep the copper area connecting the SW pin to the inductor as short and wide as

possible. At the same time the total area of this node should be minimized to help reduce radiated EMI.

See the following PCB layout resources for additional important guidelines:

•

Layout Guidelines for Switching Power Supplies

•

Simple Switcher PCB Layout Guidelines

•

Construction Your Power Supply- Layout Considerations

•

Low Radiated EMI Layout Made Simple with LM4360x and LM4600x