Thermal design notes

LNBH221

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Thermal design notes

During normal operation, the LNBH221 device dissipates some power. At rated output

current of 500mA on each section output, the voltage drop on both linear regulators lead to

a total dissipated power that is typically 2W. The heat generated requires a suitable heatsink

to keep the junction temperature below the over-temperature protection threshold.

than 40°C/W.

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.

the PCB heatsink. This area can be the inner 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 8., it is shown a suggested layout for the PSO-36 package with a dual layer PCB,

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

connected through 32 vias holes, filled by solder. This arrangement, when L=40mm,

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 8.

PowerSO-36 Suggested Pcb Heatsink Layout