Rainbow-electronics MAX1791 Manual de usuario descargar pdf (Pagina 19)

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down

Controllers for Notebooks

______________________________________________________________________________________ 19

Layout Procedure

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

minals adjacent (Q1 source, C

, C

OUT

). If possi-

ble, make all these connections on the top layer

with wide, copper-filled areas.

2) Mount the controller IC adjacent to the synchro-

nous-rectifier MOSFETs, preferably on the back

side in order to keep CS, GND, and the DL gate

drive lines short and wide. The DL gate trace must

be short and wide (measuring 50mils to 100mils

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

3) Place the V

bypass capacitor near the controller

IC.

4) Make the DC-DC controller ground connections as

follows: Near the IC, create a small analog ground

plane. Connect this plane to GND, and use this

plane for the ground connection for the REF and

bypass capacitors and FB dividers.

5) On the board’s top side (power planes), make a

star ground to minimize crosstalk between the two

sides. The top-side star ground is a star connection

of the input capacitors, side 1 low-side MOSFET.

Keep the resistance low between the star ground

and the source of the low-side MOSFETs for accu-

rate current limit. Connect the top-side star ground

(used for MOSFET, input, and output capacitors) to

the small island with a single short, wide connection

(preferably just a via).

6) Connect the output power planes directly to the out-

put filter capacitor positive and negative terminals

with multiple vias.

Chip Information

TRANSISTOR COUNT: 3520

PROCESS: S8E1FP

Figure 10. PC Board Layout Example

AGND

PGND

USE AGND PLANE TO:

- BYPASS V

AND REF

- TERMINATE EXTERNAL FB

DIVIDER (IF USED)

- PIN-STRAP CONTROL

INPUTS

USE PGND PLANE TO:

- BYPASS V

- CONNECT PGND TO THE TOPSIDE STAR GROUND

VIA TO GROUND

NOTE: EXAMPLE SHOWN IS FOR DUAL N-CHANNEL MOSFET.

CONNECT PGND TO AGND

BENEATH THE MAX1762/MAX1791 AT

ONE POINT ONLY AS SHOWN.

GND

VOUT

VBATT

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Rainbow-electronics MAX1791 Manual de usuario Pagina 19

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