AN1001

Vishay Siliconix

Document Number: 70571

12-Dec-03

www.vishay.com

1

LITTLE FOOTR TSSOP-8

The Next Step in Surface-Mount Power MOSFETs

Wharton McDaniel and David Oldham

When Vishay Siliconix introduced its LITTLE FOOT

MOSFETs, it was the first time that power MOSFETs had been

offered in a true surface-mount package, the SOIC. LITTLE

FOOT immediately found a home in new small form factor disk

drives, computers, and cellular phones.

The new LITTLE FOOT TSSOP-8 power MOSFETs are the

natural evolutionary response to the continuing demands of

many markets for smaller and smaller packages. LITTLE

FOOT TSSOP-8 MOSFETs have a smaller footprint and a

lower profile than LITTLE FOOT SOICs, while maintaining low

accomplished this by putting one or two high-density MOSFET

die in a standard 8-pin TSSOP package mounted on a custom

leadframe.

THE TSSOP-8 PACKAGE

LITTLE FOOT TSSOP-8 power MOSFETs require

approximately half the PC board area of an equivalent LITTLE

FOOT device (Figure 1). In addition to the reduction in board

area, the package height has been reduced to 1.1 mm.

Top View

Side View

Figure 1.

An TSSOP-8 Package Next to a SOIC-8 Package

with Views from Both Top and Side

This is the low profile demanded by applications such as

PCMCIA cards.

It reduces the power package to the same height as many

resistors and capacitors in 0805 and 0605 sizes. It also allows

placement on the “passive” side of the PC board.

The standard pinouts of the LITTLE FOOT TSSOP-8

packages have been changed from the standard established

by LITTLE FOOT. This change minimizes the contribution of

transfer of heat out of the package.

Figure 2 shows the pinouts for a single-die TSSOP. Notice that

both sides of the package have Source and Drain

connections, whereas LITTLE FOOT has the Source and Gate

connections on one side of the package, and the Drain

connections are on the opposite side.

Figure 2.

Pinouts for Single Die TSSOP

Drain

Source

Source

Gate

Source

Source

Drain

Drain

Figure 3 shows the standard pinouts for a dual-die TSSOP-8.

In this case, the connections for each individual MOSFET

occupy one side.

Figure 3.

Pinouts for Dual-Die TSSOP

Drain 1

Source 1

Source 1

Gate 1

Source 2

Source 2

Drain 2

Gate 2