AN813

Vishay Siliconix

Document Number: 71236

12-Dec-03

www.vishay.com

1

Single-Channel LITTLE FOOTR SC-70 3-Pin and 6-Pin MOSFET

Recommended Pad Pattern and Thermal Peformance

INTRODUCTION

BASIC PAD PATTERNS

This technical note discusses pin-outs, package outlines, pad

patterns, evaluation board layout, and thermal performance

for single-channel LITTLE FOOT power MOSFETs in the

SC-70 package. These new Vishay Siliconix devices are

intended for small-signal applications where a miniaturized

package is needed and low levels of current (around 350 mA)

need to be switched, either directly or by using a level shift

configuration. Vishay provides these single devices with a

range of on-resistance specifications and in both traditional

3-pin and new 6-pin versions. The new 6-pin SC-70 package

enables improved on-resistance values and enhanced

thermal performance compared to the 3-pin package.

PIN-OUT

Figure 1 shows the pin-out description and Pin 1 identification

for the single-channel SC-70 device in both 3-pin and 6-pin

configurations. The pin-out of the 6-pin device allows the use

of four pins as drain leads, which helps to reduce on-resistance

and junction-to-ambient thermal resistance.

SOT-323

SC-70 (3-LEADS)

1

2

3

Top View

G

S

D

SOT-363

SC-70 (6-LEADS)

6

4

1

2

3

5

Top View

D

D

G

FIGURE 1.

For package dimensions see outline drawings:

SC-70 (3-Leads) (http://www.vishay.com/doc?71153)

SC-70 (6-Leads) (http://www.vishay.com/doc?71154)

See Application Note 826, Recommended Minimum Pad

Patterns With Outline Drawing Access for Vishay Siliconix

MOSFETs, (http://www.vishay.com/doc?72286) for the basic

pad layout and dimensions for the 3-pin SC-70 and the 6-pin

SC-70. These pad patterns are sufficient for the low-power

applications for which this package is intended. Increasing the

pad pattern has little effect on thermal resistance for the 3-pin

device, reducing it by only 10% to 15%. But for the 6-pin

device, increasing the pad patterns yields a reduction in

thermal resistance on the order of 35% when using a 1-inch

square with full copper on both sides of the printed circuit board

(PCB). The availability of four drain leads rather than the

traditional single drain lead allows a better thermal path from

the package to the PCB and external environment.

EVALUATION BOARDS FOR THE SINGLE

SC70-3 AND SC70-6

Figure 2 shows the 3-pin and 6-pin SC-70 evaluation boards

(EVB). Both measure 0.6 inches by 0.5 inches. Their copper

pad traces are the same as described in the previous section,

Basic Pad Patterns. Both boards allow interrogation from the

outer pins to 6-pin DIP connections, permitting test sockets to

be used in evaluation testing.

The thermal performance of the single SC-70 has been

measured on the EVB for both the 3-pin and 6-pin devices, the

results shown in Figures 3 and 4. The minimum recommended

footprint on the evaluation board was compared with the

industry standard of 1-inch square FR4 PCB with copper on

both sides of the board.

FIGURE 2.

Front of Board SC70-3

Front of Board SC70-6

Back of Board, SC70-3 and SC70-6

ChipFETr

ChipFETr

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