Rainbow-electronics MAX8707 Manual de usuario descargar pdf (Pagina 35)

This is essential for high-power MOSFETs that

require low-impedance gate drivers to avoid shoot-

through currents.

7) When trade-offs in trace lengths must be made, it’s

preferable to allow the inductor charging path to be

made longer than the discharge path. For example,

it’s better to allow some extra distance between the

input capacitors and the high-side MOSFET than to

allow distance between the inductor and the low-

side MOSFET or between the inductor and the out-

put filter capacitor.

Layout Procedure

1) Place the power components first, with ground termi-

nals adjacent (low-side MOSFET source, C

, C

OUT

and D1 anode). If possible, make all these connec-

tions on the top layer with wide, copper-filled areas.

2) Mount the driver IC adjacent to the low-side

MOSFETs. The DL gate traces must be short and

wide (50mils to 100mils wide if the MOSFET is 1in

from the driver IC).

3) Group the gate-drive components (BST diodes and

capacitors, V

bypass capacitor) together near the

driver IC.

4) Make the DC-DC controller ground connections as

shown in the Standard Application Circuits. This dia-

gram can be viewed as having three separate

ground planes: input/output ground, where all the

high-power components go; the power ground

plane, where the PGND pin, V

bypass capacitor,

and driver IC ground connection go; and the con-

troller’s analog ground plane, where sensitive ana-

log components, the master’s GND pin, and the V

bypass capacitor go. The controller’s analog ground

plane (GND) must meet the power ground plane

(PGND) only at a single point directly beneath the

IC. The power ground plane should connect to the

high-power output ground with a short, thick metal

trace from PGND to the source of the low-side

MOSFETs (the middle of the star ground).

5) Connect the output power planes (V

CORE

and sys-

tem ground planes) directly to the output-filter-

capacitor positive and negative terminals with

multiple vias. Place the entire DC-DC converter cir-

cuit as close to the CPU as is practical.

MAX8707

Multiphase, Fixed-Frequency Controller for

AMD Hammer CPU Core Power Supplies

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