FN7360 Rev 5.00

Page 13 of 14

November 5, 2007

EL7554

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Thermal Management

The EL7554IRE is packaged in a thermally-efficient

HTSSOP-28 package, which utilizes the exposed thermal

pad at the bottom to spread heat through PCB metal.

Therefore:

1. The thermal pad must be soldered to the PCB

2. Maximize the PCB area

3. If a multiple layer PCB is used, thermal vias (13 to 25 mil)

must be placed underneath the thermal pad to connect to

ground plane(s). Do not place thermal reliefs on the vias.

Figure 25 shows a typical connection.

The thermal resistance for this package is as low as +26°C/W

for 2 layer PCB of 0.39" thickness (see Figure 9). The actual

The thermal performance of the IC is heavily dependent on

the layout of the PCB. The user should exercise care during

the design phase to ensure the IC will operate within the

recommended environmental conditions.

FIGURE 25. PCB LAYOUT - 28 Ld HTSSOP PACKAGE

Layout Considerations

The layout is very important for the converter to function

properly. Follow these tips for best performance:

1. Separate the Power Ground ( ) and Signal Ground (

);

connect them only at one point right at the SGND pin

pins as possible

3. Make as small as possible the loop from LX pins to L to

5. Maximize the copper area around the PGND pins; do not

place thermal relief around them

6. Thermal pad should be soldered to PCB. Place several

via holes under the chip to the ground plane to help heat

dissipation

The demo board is a good example of layout based on this

outline. Please refer to the EL7554 Application Brief.

GROUND PLANE

CONNECTION

COMPONENT SIDE

CONNECTION