lnbh221 STMicroelectronics, lnbh221 Datasheet - Page 18

• Manufacturer Part Number: lnbh221
• Description: Dual Lnb Supply And Control Ic With Step-up Converter And I2c Interface
• Manufacturer: STMicroelectronics

Thermal design notes
8
Figure 8.
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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.
Assuming a 45°C temperature inside the Set-Top-Box case, the total R
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.
Given for the PSO-36 package an R
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
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,
achieves an R
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.
PowerSO-36 Suggested Pcb Heatsink Layout
8., it is shown a suggested layout for the PSO-36 package with a dual layer PCB,
thJA
of about 28°C/W.
thJC
equal to 2°C/W, a maximum of 38°C/W are left to
thJC
has to be less
LNBH221