MAX1717 Maxim, MAX1717 Datasheet - Page 31

• Manufacturer Part Number: MAX1717
• Description: Dynamically Adjustable / Synchronous Step-Down Controller for Notebook CPUs
• Manufacturer: Maxim

2) Mount the controller IC adjacent to MOSFET Q2,
3) Group the gate-drive components (BST diode and
4) Make the DC-DC controller ground connections as
Figure 12. Power-Stage PC Board Layout Example
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).
capacitor, V
controller IC.
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
CONNECT LOCAL ANALOG GROUND PLANE DIRECTLY TO GND FROM
THE SIDE OPPOSITE THE V
CURRENTS FROM FLOWING IN THE ANALOG GROUND PLANE.
CONNECT TO LOCAL PLANE ONLY
ALL ANALOG GROUNDS
NOTES: "STAR" GROUND IS USED.
D1 IS DIRECTLY ACROSS Q2.
DD
Step-Down Controller for Notebook CPUs
V
CC
REF
______________________________________________________________________________________
CC
bypass capacitor) together near the
DD
CAPACITOR GND TO AVOID V
MAX1717
Dynamically Adjustable, Synchronous
V
DD
GND
DD
VIA TO SOURCE
bypass capacitors
DD
VIA TO LX
GROUND
VIA TO GND
NEAR Q2 SOURCE
OF Q2
Q1
INDUCTOR DISCHARGE PATH HAS LOW DC RESISTANCE
D1
Q2
5) Connect the output power planes (VCORE and system
L1
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.
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.
CIN
V
BATT
COUT
GND IN
R6
VIA TO FB
AND FBS
GND
OUT
V
OUT
31