THS3120 datasheet(21/28 Pages) TI

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Pin 1

Top View

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PowerPAD™ LAYOUT CONSIDERATIONS

POWER DISSIPATION AND THERMAL

THS3120, THS3121

SLOS420A – SEPTEMBER 2003 – REVISED NOVEMBER 2003

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-

fore, the holes under the THS3120 / THS3121

PowerPAD package should make their connec-

tion to the internal ground plane with a complete

connection around the entire circumference of the

plated-through hole.

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

minals of the package and the thermal pad area

with its five holes exposed. The bottom-side

solder mask should cover the five holes of the

thermal pad area. This prevents solder from

Figure 58. DGN PowerPAD PCB Etch and Via

being pulled away from the thermal pad area

Pattern

during the reflow process.

7. Apply solder paste to the exposed thermal pad

area and all of the IC terminals.

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

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

simply placed in position and run through the

Figure 58. There should be etch for the leads as

solder reflow operation as any standard sur-

well as etch for the thermal pad.

face-mount component. This results in a part that

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

is properly installed.

These holes should be 10 mils in diameter. Keep

them small so that solder wicking through the

holes is not a problem during reflow.

CONSIDERATIONS

3. Additional vias may be placed anywhere along

The THS3120 and THS3121 incorporates automatic

the thermal plane outside of the thermal pad

thermal shutoff protection. This protection circuitry

area. This helps dissipate the heat generated by

shuts down the amplifier if the junction temperature

the THS3120 / THS3121 IC. These additional

exceeds approximately 160

°C. When the junction

vias may be larger than the 10-mil diameter vias

temperature reduces to approximately 140

°C, the

directly under the thermal pad. They can be

amplifier turns on again. But, for maximum perform-

larger because they are not in the thermal pad

ance and reliability, the designer must take care to

area to be soldered so that wicking is not a

ensure that the design does not exeed a junction

problem.

temperature of 125

°C. Between 125°C and 150°C,

4. Connect all holes to the internal ground plane.

damage does not occur, but the performance of the

Note that the PowerPAD is electrically isolated

amplifier begins to degrade and long term reliability

from the silicon and all leads. Connecting the

suffers. The thermal characteristics of the device are

PowerPAD to any potential voltage such as VS-,

dictated by the package and the PC board. Maximum

is acceptable as there is no electrical connection

power dissipation for a given package can be calcu-

to the silicon.

lated using the following formula.

5. When connecting these holes to the ground

plane, do not use the typical web or spoke via

connection methodology. Web connections have

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