SM8172A Datasheet, PDF (15/17 Pages) Nippon Precision Circuits Inc – 2-output Power Supply IC

SM8172A
14-4. Mounting
The package rear surface is metallic, and can be connected to the printed circuit board pattern as a heatsink.
The connected pattern should be tied to GND level. Furthermore, use of a thermal via structure on the PCB or
other technology should be used to provide sufficient heat dissipation. Use a printed circuit board with 4 or
more layers. The PCB wiring ratio^*1 should exceed 200%, where the wiring ratio is the sum total of printed
wiring pattern surface area relative to the circuit board surface area.
*1: Determining the wiring pattern ratio
Example: 4-layer board with the same wiring pattern on 4 layers (left), where the wiring pattern surface
area on each layer is represented by S1, and the non-wired surface area is represented by S2. The wiring
pattern is connected directly to the IC, and each layer’s wiring pattern is connected to the IC by through
holes. The circuit board surface area seen from above is S1 + S2. First, calculate the board surface area,
here represented by S1 + S2. Next, calculate the wiring pattern surface area on each layer connected to the
IC, represented here by S1. Calculate the total wiring pattern surface area for all 4 layers, in this example 4
× S1. Finally, calculate the wiring ratio percentage using the following equation: (Wiring ratio) = (Total
wiring pattern surface area connected to the IC) / (PCB surface area) × 100. In this example, 4 × S1/(S1 +
S2) × 100 [%], or a wiring ratio of 200% when S1 = S2.
S1
S2
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