12

LT1371

APPLICATIO S I FOR ATIO

LT1371T7

TAB

SYSTEM GROUND

FLOATING NODE

(TAB TIES INTERNALLY

TO PIN 4 GROUND)

4

2

1

5

7

GND

GND

FB

LT1371 • F07

Figure 7. Tab Connections for Vertically Mounted T7 Package

T7 Package Layout Considerations

Electrical connection to the tab of a T7 package is required

for proper device operation. If the tab is tied directly to the

ground plane (Figure 4) no other considerations are nec-

essary. If the tab is not connected directly to the ground

plane, as in a vertically mounted application, a separate

electrical connection from the tab to a “floating node” is

nents and output feedback resistor divider are then con-

nected to the floating node. This is shown schematically in

Figure 7. All other system ground connections are made to

Pin 4.

The electrical connection from the T7 package tab to the

floating node must be a low resistance (< 0.1

Ω), low

inductance (< 20nH) path which can be accomplished with

a jumper wire or an electrically conductive heat sink.

Bolt the jumper wire directly to the tab using a solder tail

to maintain low resistance. The jumper wire length should

not exceed 3/4 inch of 24 AWG gauge wire or larger to

minimize the inductance.

Vertically mounted electrically conductive heat sinks are

available from many heat sink manufacturers. These heat

sinks also have tabs that solder directly to the board

creating the required low resistance, low inductance path

from the tab to the floating node. The tab should be bolted

or soldered directly to the heat sink to maintain low

resistance. Heat sinks are available in clip-on styles but are

only recommended if the tab to heat sink contact resis-

tance can be maintained below 0.1

Ω for the life of the

product.

More Help

For more detailed information on switching regulator

circuits, please see Application Note 19. Linear Technol-

ogy also offers a computer software program,

SwitcherCAD, to assist in designing switching converters.

In addition, our Applications Department is always ready

to lend a helping hand.