Rainbow Electronics MAX8712 - Manual (Page 22)

PC Board Layout Guidelines
Careful PC board layout is important for proper opera-
tion. Use the following guidelines for good PC board
layout:
1) Create a power ground island consisting of the lin-
ear-regulator input and output-capacitor ground
connections, the GND pin, and the capacitor
ground connections for the charge-pump regula-
tors. Connect all these together with short, wide
traces or a small ground plane. Maximizing the
width of the power ground traces improves efficien-
cy. Create an analog ground island consisting of all
the feedback-divider ground connections, the oper-
ational-amplifier divider ground connection, the REF
capacitor ground connection, the MODE capacitor
ground connection, the DLP capacitor ground con-
nection, and the device’s exposed backside pad.
Connect the analog ground island and the power
ground island by connecting the GND pin directly to
the exposed backside pad. Make no other connec-
tions between these separate ground islands.
2) Place all feedback voltage-divider resistors as close
to their respective feedback pins as possible. The
divider’s center trace should be kept short. Placing
the resistors far away causes their FB traces to
become antennas that can pick up noise from the
switching nodes of the charge pumps. Avoid running
any feedback trace near these switching nodes.
3) Place IN, INL, SUPB, SUPCP, and REF pin bypass
capacitors close to the IC. The ground connection
of the IN bypass capacitor should be connected
directly to the GND pin with a wide trace.
4) Minimize the length and maximize the width of the
traces between the output capacitors and the load
for best transient responses.
5) Minimize the size of the switching nodes (DRVP and
DRVN). Keep the switching nodes away from feed-
back nodes (FBL, FBP, and FBN) and the analog
ground. Use DC traces as a shield if necessary.
Refer to the MAX8710 evaluation kit for an example of
proper board layout.
Pin Configurations (continued)
MAX8710/MAX8711/MAX8712
Low-Cost Linear-Regulator
LCD Panel Power Supplies
22 ______________________________________________________________________________________
16
1
2
3
4
12
11
10
9
15 14 13
5 6 7 8
FBN
FBN
OUTL DRVN DRVP
DLP FBL
DLP FBL SHDN
FBP
SUPB
OUTB
GND
POSB
INL
NEGB
IN
OUTL DRVN DRVP
REF
TOP VIEW
MAX8711
THIN QFN 4mm x 4mm
12 11 10
4 5 6
1
2 INL
3
9
8
7 IN
FBP
SHDN
GND
MAX8712
REF
THIN QFN 4mm x 4mm
Chip Information
TRANSISTOR COUNT: 3946
PROCESS: BiCMOS