Rev F: /0/06

SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator

© Copyright 2006 Sipex Corporation

SP765X Thermal Resistance

The SP765X family has been tested with a

variety of footprint layouts along with differ-

ent copper area and thermal resistance has

been measured. The layouts were done on

4 layer FR4 PCB with the top and bottom

layers using 3oz copper and the power and

ground layers using oz copper.

For the Minimum footprint, only about 0.

square inch (of 3 ounces of) Copper was

used on the top or footprint layer, and this

layer had no vias to connect to the 3 other

layers. For the Medium footprint, about 0.7

square inches (of 3 ounces of) Copper was

used on the top layer, but vias were used

to connect to the other 3 layers. For the

Maximum footprint, about .0 square inch

(of 3 ounces of) Copper was used on the top

layer and many vias were used to connect

to the 3 other layers.

The results show that only about 0.7 square

inches (of 3 ounces of) Copper on the top

layer and vias connecting to the 3 other

layers are needed to get the best thermal

resistance of 36°C/W. Adding area on the

top beyond the 0.7 square inches did not

reduce thermal resistance.

Using a minimum of 0. square inches of

(3 ounces of) Copper on the top layer with

no vias connecting to the 3 other layers

produced a thermal resistance of 44°C/W.

This thermal impedance is only 22% higher

than the medium and large footprint layouts,

indicating that space constrained designs

canstillbenefitthermallyfromthePowerblox

family of ICs. This indicates that a minimum

footprintof0.squareinch,ifusedona4layer

board, can produce 44°C/W thermal resis-

tance. This approach is still very worthwhile

if used in a space constrained design.

The following page shows the footprint

layouts from an ORCAD file. The thermal

data was taken for still air, not with forced

air. If forced air is used, some improvement

in thermal resistance would be seen.

SP765X Thermal Resistance

4 Layer Board:

Top Layer 3ounces Copper

GND Layer 1ounce Copper

Power Layer ounce Copper

Bottom Layer 3ounces Copper

Minimum Footprint: 44°C/W

Top Layer: 0. square inch

No Vias to other 3 Layers

Medium Footprint: 36°C/W

Top Layer: 0.7 square inch

Vias to other 3 Layers

Maximum Footprint: 36°C/W

Top Layer: .0 square inch

Vias to other 3 Layers

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