ISL85415

7. Application Guidelines

FN8373 Rev.5.01

Page 28 of 30

Jun.4.20

7.8

Layout Considerations

Proper layout of the power converter minimizes EMI and noise and insure first pass success of the design. Printed

Circuit Board (PCB) layouts are provided in multiple formats on the website. In addition, Figure 64 illustrates the

important points in the PCB layout. Physically, the PCB layout of the ISL85415 is simple.

A multi-layer printed circuit board with GND plane is recommended. Figure 64 shows the connections of the

critical components in the converter. Note: capacitors CIN and COUT could each represent multiple physical

capacitors. The most critical connections are to tie the PGND pin to the package GND pad and then use vias to

directly connect the GND pad to the system GND plane. This connection of the GND pad to system plane ensures

a low impedance path for all return current, and an excellent thermal path to dissipate heat. With this connection

made, place the high frequency MLCC input capacitor near the VIN pin and use vias directly at the capacitor pad

to tie the capacitor to the system GND plane.

The boot capacitor is easily placed on the PCB side opposite the controller IC and two vias directly connect the

capacitor to BOOT and PHASE.

Place a 1µF MLCC near the VCC pin and directly connect its return with a via to the system GND plane.

Place the feedback divider close to the FB pin and do not route any feedback components near PHASE or BOOT.

If external components are used for SS, COMP, or FS, the same advice applies.

Figure 64. Printed Circuit Board Power Planes and Islands

L1

COUT

CVIN

CSS

RFS