Rainbow Electronics MAX1791 - Manual (Page 19)

MAX1762/MAX1791
High-Efficiency, 10-Pin µMAX, Step-Down
Controllers for Notebooks
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Layout Procedure
1) Place the power components first, with ground ter-
minals adjacent (Q1 source, C IN , 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
L
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
V
VP 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
CC AND REF
- TERMINATE EXTERNAL FB
DIVIDER (IF USED)
- PIN-STRAP CONTROL
INPUTS
USE PGND PLANE TO:
- BYPASS V
VP
- 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
P1
N1
VOUT
VL
VBATT
L1
C2
C1
D1