LT8613 datasheet(19/24 Pages) LINER

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LT8613

8613f

applicaTions inForMaTion

Figure 6. Recommended PCB Layout for the LT8613

PCB Layout

ForproperoperationandminimumEMI,caremustbetaken

during printed circuit board layout. Figure 6 shows the

recommended component placement with trace, ground

plane and via locations. Note that large, switched currents

flow in the LT8613’s VINpins,PGNDpins,andtheinputca-

pacitor(C1).Theloopformedbytheinputcapacitorshould

be as small as possible by placing the capacitor adjacent

to the VIN and PGND pins. When using a physically large

input capacitor the resulting loop may become too large

in which case using a small case/value capacitor placed

close to the VIN and PGND pins plus a larger capacitor

further away is preferred. These components, along with

the inductor and output capacitor, should be placed on the

samesideofthecircuitboard,andtheirconnectionsshould

be made on that layer. Place a local, unbroken ground

plane under the application circuit on the layer closest to

the surface layer. The SW and BOOST nodes should be

as small as possible. Finally, keep the FB and RT nodes

small so that the ground traces will shield them from the

SW and BOOST nodes. The exposed pad on the bottom of

the package must be soldered to ground so that the pad

is connected to ground electrically and also acts as a heat

sink thermally. To keep thermal resistance low, extend the

ground plane as much as possible, and add thermal vias

under and near the LT8613 to additional ground planes

within the circuit board and on the bottom side.

High Temperature Considerations

For higher ambient temperatures, care should be taken in

the layout of the PCB to ensure good heat sinking of the

LT8613. The exposed pad on the bottom of the package

must be soldered to a ground plane. This ground should

be tied to large copper layers below with thermal vias;

these layers will spread heat dissipated by the LT8613.

Placing additional vias can reduce thermal resistance

further. The maximum load current should be derated

as the ambient temperature approaches the maximum

junction rating. Power dissipation within the LT8613 can

be estimated by calculating the total power loss from an

efficiencymeasurementandsubtractingtheinductorloss.

ThedietemperatureiscalculatedbymultiplyingtheLT8613

power dissipation by the thermal resistance from junction

to ambient. The LT8613 will stop switching and indicate

a fault condition if safe junction temperature is exceeded.

VOUT

8613 F06

OUTLINE OF LOCAL

GROUND PLANE

BST

BIAS

INTVCC

GND

VOUT

SYNC

TR/SS

EN/UV

VIN

IMON

ISN

ISP

ICTRL

VOUT LINE TO BIAS

VOUT LINE TO ISN

LINE TO ISP

VIAS TO GROUND PLANE

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