Application Note 1793

3

AN1793.1

December 6, 2012

However, if the output voltage is increased or the board is

operated at elevated temperatures, then the available current is

determine the output current available.

For layout of designs using the ISL8225M, the thermal

performance can be improved by adhering to the following

design tips:

1. Use the top and bottom layers to carry the large current.

VOUT1, VOUT2, Phase 1, Phase 2, PGND, VIN1 and VIN2

should have large, solid planes. Place enough thermal vias to

connect the power planes in different layers under and

around the module.

2. Phase 1 and Phase 2 pads are switching nodes that generate

switching noise. Keep these pads under the module. For

noise-sensitive applications, it is recommended to keep

phase pads only on the top and inner layers of the PCB; do not

place phase pads exposed to the outside on the bottom layer

of the PCB. To improve the thermal performance, the phase

pads can be extended in the inner layer, as shown in Phase 1

and Phase 2 pads on layer 2 (Figure 5) for this dual 15A

evaluation board. Make sure that layer 1 and layer 3 have the

GND layers to cover the extended areas of phase pads at

layer 2 to avoid noise coupling.

3. Place the modules evenly on the board and leave enough

space between modules. If the board space is limited, try to

put the modules with low power loss closely together (i.e. low

loss.

4. If the ambient temperature is high or the board space is

limited, airflow is needed to dissipate more heat from the

modules. A heat sink can also be applied to the top side of the

module to further improve the thermal performance (heat

sink recommendation: Aavid Thermalloy, part number