AN2407

Board layout considerations

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Board layout considerations

Due to the small size of the MLP package, it is very important to use a good thermal PC

board layout to maximize the available charge current. The thermal path for the heat

generated by the IC is from the die to the copper lead frame, through the package leads,

(especially the ground lead) to the PC board copper. The PC board copper is the heat sink.

The footprint copper pads should be as wide as possible and expand out to larger copper

areas to spread and dissipate the heat to the surrounding ambient. Feed-through vias to

inner or backside copper layers are also useful in improving the overall thermal performance

of the charger. Other heat sources on the board, not related to the charger, must also be

considered when designing a PC board layout because they will affect overall temperature

rise and the maximum charge current.

Table 1 lists thermal resistance for several different board sizes and copper areas.

Appendix A: Board layout on page 12 contains an illustration of the complete assembly

board.

Table 1.

Measured thermal resistance (2-layer board)

Copper area

Board area

Thermal resistance

junction-to-ambient

Top

Bottom

125°C/W

125°C/W

130°C/W

135°C/W

150°C/W