AN814

Vishay Siliconix

Document Number: 71237

12-Dec-03

www.vishay.com

1

Dual-Channel LITTLE FOOTR SC-70 6-Pin MOSFET

Recommended Pad Pattern and Thermal Performance

INTRODUCTION

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

pad patterns, evaluation board layout, and thermal

performance for dual-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 250 mA) need to be switched, either directly or by

using a level shift configuration. Vishay provides these devices

with a range of on-resistance specifications in 6-pin versions.

The new 6-pin SC-70 package enables improved

on-resistance values and enhanced thermal performance.

PIN-OUT

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

for the dual-channel SC-70 device in the 6-pin configuration.

FIGURE 1.

SOT-363

SC-70 (6-LEADS)

6

4

1

2

3

5

Top View

For package dimensions see outline drawing SC-70 (6-Leads)

BASIC PAD PATTERNS

See Application Note 826, Recommended Minimum Pad

Patterns With Outline Drawing Access for Vishay Siliconix

SC-70. This basic pad pattern is sufficient for the low-power

applications for which this package is intended. For the 6-pin

device, increasing the pad patterns yields a reduction in

thermal resistance on the order of 20% when using a 1-inch

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

(PCB).

EVALUATION BOARDS FOR THE DUAL

SC70-6

The 6-pin SC-70 evaluation board (EVB) measures 0.6 inches

by 0.5 inches. The copper pad traces are the same as

described in the previous section, Basic Pad Patterns. The

board allows interrogation from the outer pins to 6-pin DIP

connections permitting test sockets to be used in evaluation

testing.

The thermal performance of the dual SC-70 has been

measured on the EVB with the results shown below. The

minimum recommended footprint on the evaluation board was

compared with the industry standard 1-inch square FR4 PCB

with copper on both sides of the board.

THERMAL PERFORMANCE

Junction-to-Foot Thermal Resistance

(the Package Performance)

Thermal performance for the dual SC-70 6-pin package

measured as junction-to-foot thermal resistance is 300_C/W

typical, 350_C/W maximum. The “foot” is the drain lead of the

device as it connects with the body. Note that these numbers

are somewhat higher than other LITTLE FOOT devices due to

the limited thermal performance of the Alloy 42 lead-frame

compared with a standard copper lead-frame.

Junction-to-Ambient Thermal Resistance

(dependent on PCB size)

state. Maximum ratings are 460_C/W for the dual. All figures

based on the 1-inch square FR4 test board. The following

example shows how the thermal resistance impacts power

dissipation for the dual 6-pin SC-70 package at two different

ambient temperatures.