GND

VIN

SW

VOUT

L1

Via to Ground Plane

SW

BST

RCL

RTN

FB

RT/SD

VCC

VIN

LM5008

D1

CIN

RFB2

COUT

RFB1

CB

CVCC

RT

Via

to VIN

19

LM5008A

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SNVS583H – MARCH 2009 – REVISED OCTOBER 2018

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10 Layout

10.1 Layout Guidelines

The LM5008A regulation and overvoltage comparators are very fast, and as such responds to short-duration

noise pulses. Layout considerations are therefore critical for optimum performance:

1. Minimize the area of the high di/dt switching current loop consisting of the VIN pin, input ceramic capacitor,

SW node and freewheeling power diode. Keep the input capacitor as close as possible to the VIN pin and

route a short, direct connection to the RTN pin using polygon copper pours.

2. Minimize SW copper area to reduce radiated noise related to high dv/dt.

3. Locate all components as physically close as possible to their respective pins, thereby minimizing noise

pickup in the printed-circuit tracks.

4. The FB trace should be away from noise sources and inductors. The lower feedback resistor should connect

to ground close to the IC RTN.

If the internal dissipation of the LM5008A converter produces excessive junction temperatures during normal

operation, optimal use of the PCB ground plane can help considerably to dissipate heat. The exposed pad on the

bottom of the WSON-8 package can be soldered to a ground plane on the PCB, and that plane should extend

out from beneath the IC to help dissipate the heat. Additionally, the use of wide PCB traces for power connection

can also help conduct heat away from the IC. Judicious positioning of the LM5008A converter within the end

product, along with use of any available air flow (forced or natural convection), can help reduce the operating

junction temperature.

10.2 Layout Example

Figure 16. LM5008A PCB Layout Example