ADS1174IPAPR datasheet(29/35 Pages) TI

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PowerPAD PCB Layout Considerations for the

Additional PowerPAD Package Information

13mils(0.33mm)

Package

ThermalPad

Component

Traces

ThermalVia

Component(top)Side

GroundPlane

PowerPlane

Solder(bottom)Side

ThermalIsolation

(powerplaneonly)

Package

ThermalPad

(bottomtrace)

ADS1174

ADS1178

SBAS373 – OCTOBER 2007

The via connections to the thermal pad and internal

ADS1174/78

ground plane should be plated completely around the

hole, as opposed to the typical web or spoke thermal

Figure 30 shows the recommended layer structure for

relief connection. Plating entirely around the thermal

thermal

management

when

using

PowerPad

via provides the most efficient thermal connection to

package on a 4-layer PCB design. Note that the

the ground plane.

thermal pad is placed on both the top and bottom

sides of the board. The ground plane is used as the

heat-sink, while the power plane is thermally isolated

from the thermal vias.

Texas

Instruments

publishes

the

PowerPAD

Thermally Enhanced Package Application Report (TI

Figure 31 shows the required thermal pad etch

literature number SLMA002), available for download

pattern for the 64-lead HTQFP package used for the

at www.ti.com, which provides a more detailed

ADS1174/78. Nine 13mil (0.33mm) thermal vias

discussion

PowerPAD

design

and

layout

plated with one ounce of copper are placed within the

considerations. Before attempting a board layout with

thermal pad area for the purpose of connecting the

the

ADS1174/78,

recommended

that

the

pad to the ground plane layer. The ground plane is

hardware engineer and/or layout designer be familiar

used as a heatsink in this application. It is very

with the information contained in this document.

important that the thermal via diameter be no larger

than 13mils in order to avoid solder wicking during

the reflow process. Solder wicking results in thermal

voids that reduce heat dissipation efficiency and

hamper heat flow away from the IC die.

Figure 30. Recommended PCB Structure for a 4-Layer Board

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