THS3096PWPR datasheet(23/34 Pages) TI

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PowerPAD™ LAYOUT CONSIDERATIONS

POWER DISSIPATION AND THERMAL

Dmax

Tmax * TA

where:

PDmax is the maximum power dissipation in the amplifier (W).

Tmax is the absolute maximum junction temperature (°C).

TA is the ambient temperature (°C).

θJA = θJC + θCA

θJC is the thermal coeffiecient from the silicon junctions to

the case (

°C/W).

θCA is the thermal coeffiecient from the case to ambient

air (

°C/W).

THS3092

THS3096

SLOS428A – DECEMBER 2003 – REVISED FEBRUARY 2004

CONSIDERATIONS

1. PCB with a top side etch pattern as shown in

Figure 67. There should be etch for the leads as

The

THS3092/6

incorporates

automatic

thermal

well as etch for the thermal pad.

shutoff protection. This protection circuitry shuts down

the amplifier if the junction temperature exceeds

2. Place 13 holes in the area of the thermal pad.

approximately 160

°C. When the junction temperature

These holes should be 10 mils in diameter. Keep

reduces to approximately 140

°C, the amplifier turns

them small so that solder wicking through the

on again. But, for maximum performance and re-

holes is not a problem during reflow.

liability, the designer must take care to ensure that

3. Additional vias may be placed anywhere along

the design does not exeed a junction temperature of

the thermal plane outside of the thermal pad

125

°C. Between 125°C and 150°C, damage does not

area. This helps dissipate the heat generated by

occur, but the performance of the amplifier begins to

the THS3092/6 IC. These additional vias may be

degrade and long term reliability suffers. The thermal

larger than the 10-mil diameter vias directly under

characteristics of the device are dictated by the

the thermal pad. They can be larger because

package

and

the

board.

Maximum

power

they are not in the thermal pad area to be

dissipation for a given package can be calculated

soldered so that wicking is not a problem.

using the following formula.

4. Connect all holes to the internal ground plane.

Note that the PowerPAD is electrically isolated

from the silicon and all leads. Connecting the

PowerPAD to any potential voltage such as VS-,

is acceptable as there is no electrical connection

to the silicon.

5. When connecting these holes to the ground

plane, do not use the typical web or spoke via

connection methodology. Web connections have

a high thermal resistance connection that is

useful for slowing the heat transfer during

soldering operations. This makes the soldering of

vias that have plane connections easier. In this

application, however, low thermal resistance is

desired for the most efficient heat transfer. There-

For systems where heat dissipation is more critical,

fore, the holes under the THS3092/6 PowerPAD

the THS3092 is offered in an 8-pin SOIC (DDA) with

package should make their connection to the

PowerPAD package, and the THS3096 is offered in a

internal ground plane with a complete connection

14-pin TSSOP (PWP) with PowerPAD package for

around

the

entire

circumference

the

even better thermal performance. The thermal coef-

plated-through hole.

ficient for the PowerPAD packages are substantially

6. The top-side solder mask should leave the ter-

improved over the traditional SOIC. Maximum power

minals of the package and the thermal pad area

dissipation levels are depicted in the graph for the

with its 13 holes exposed. The bottom-side solder

available packages. The data for the PowerPAD

mask should cover the 13 holes of the thermal

packages assume a board layout that follows the

pad area. This prevents solder from being pulled

PowerPAD layout guidelines referenced above and

away from the thermal pad area during the reflow

detailed in the PowerPAD application note (literature

process.

number SLMA002). The following graph also illus-

7. Apply solder paste to the exposed thermal pad

trates the effect of not soldering the PowerPAD to a

area and all of the IC terminals.

PCB. The thermal impedance increases substantially

which may cause serious heat and performance

8. With these preparatory steps in place, the IC is

issues. Be sure to always solder the PowerPAD to

simply placed in position and run through the

the PCB for optimum performance.

solder

reflow

operation

any

standard

surface-mount component. This results in a part

that is properly installed.

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