LNBH21

12/20

THERMAL DESIGN NOTES

During normal operation, the LNBH21 device dissipates some power. At maximum rated output current

(750mA), the voltage drop on the linear regulator lead to a total dissipated power that is typically 1.65W.

The heat generated requires a suitable heatsink to keep the junction temperature below the over

temperature protection threshold. Assuming a 45°C temperature inside the Set-Top-Box case, the total

While this can be easily achieved using a through-hole power package that can be attached to a small

heatsink or to the metallic frame of the receiver, a surface mount power package must rely on PCB

solutions whose thermal efficiency is often limited. The simplest solution is to use a large, continuous

copper area of the GND layer to dissipate the heat coming from the IC body.

GND layer of a multi-layer PCB, or, in a dual layer PCB, an unbroken GND area even on the opposite side

where the IC is placed. In figure 4, it is shown a suggested layout for the PSO-20 package with a dual

layer PCB, where the IC exposed pad connected to GND and the square dissipating area are thermally

of about 32°C/W.

Different layouts are possible, too. Basic principles, however, suggest to keep the IC and its ground

exposed pad approximately in the middle of the dissipating area; to provide as many vias as possible; to

design a dissipating area having a shape as square as possible and not interrupted by other copper

traces.

Figure 4 : PowerSO-20 SUGGESTED PCB HEATSINK LAYOUT