Rainbow-electronics MAX1717 Bedienungsanleitung PDF herunterladen (Seite 31)

MAX1717

Dynamically Adjustable, Synchronous

Step-Down Controller for Notebook CPUs

______________________________________________________________________________________ 31

is at the junction of the inductor and the positioning

resistor.

7) Route high-speed switching nodes away from sensitive

analog areas (CC, REF, ILIM). Make all pin-strap

control input connections (SKP/SDN, ILIM, etc.) to ana-

log ground or V

rather than power ground or V

Layout Procedure

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

nals adjacent (Q2 source, CIN-, COUT-, D1 anode).

If possible, make all these connections on the top

layer with wide, copper-filled areas.

2) Mount the controller IC adjacent to MOSFET Q2,

preferably on the back side opposite Q2 in order to

keep LX-GND current-sense lines and the DL drive line

short and wide. The DL gate trace must be short and

wide, measuring 10 to 20 squares (50mils to 100mils

wide if the MOSFET is 1 inch from the controller IC).

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

capacitor, V

bypass capacitor) together near the

controller IC.

4) Make the DC-DC controller ground connections as

shown in Figure 12. This diagram can be viewed as

having three separate ground planes: output ground,

where all the high-power components go; the GND

plane, where the GND pin and V

bypass capacitors

go; and an analog ground plane where sensitive

analog components go. The analog ground plane

and GND plane must meet only at a single point

directly beneath the IC. These two planes are then

connected to the high-power output ground with a

short connection from GND to the source of the low-

side MOSFET Q2 (the middle of the star ground).

This point must also be very close to the output

capacitor ground terminal.

5) Connect the output power planes (VCORE and system

ground planes) directly to the output filter capacitor

positive and negative terminals with multiple vias.

Place the entire DC-DC converter circuit as close to

the CPU as is practical.

BATT

GND IN

COUT

VIA TO FB

AND FBS

VIA TO LX

VIA TO SOURCE

OF Q2

VIA TO GND

NEAR Q2 SOURCE

INDUCTOR DISCHARGE PATH HAS LOW DC RESISTANCE

GND

OUT

REF

ALL ANALOG GROUNDS

CONNECT TO LOCAL PLANE ONLY

NOTES: "STAR" GROUND IS USED.

D1 IS DIRECTLY ACROSS Q2.

CONNECT LOCAL ANALOG GROUND PLANE DIRECTLY TO GND FROM

THE SIDE OPPOSITE THE V

CAPACITOR GND TO AVOID V

GROUND

CURRENTS FROM FLOWING IN THE ANALOG GROUND PLANE.

MAX1717

CIN

GND

Figure 12. Power-Stage PC Board Layout Example

1 2 ... 26 27 28 29 30 31 32 33

Kommentare zu diesen Handbüchern

Keine Kommentare

Rainbow-electronics MAX1717 Bedienungsanleitung Seite 31

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Sensoren Rainbow-electronics MAX1717