MAX16814_15 Datasheet, PDF (21/25 Pages) Maxim Integrated Products – Integrated, 4-Channel, High-Brightness LED Driver with High-Voltage DC-DC Controller

MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
PCB Layout Considerations
LED driver circuits based on the MAX16814 device use
a high-frequency switching converter to generate the
voltage for LED strings. Take proper care while laying
out the circuit to ensure proper operation. The switching-
converter part of the circuit has nodes with very fast
voltage changes that could lead to undesirable effects
on the sensitive parts of the circuit. Follow the guidelines
below to reduce noise as much as possible:
1) Connect the bypass capacitor on VCC and DRV as
close to the device as possible and connect the
capacitor ground to the analog ground plane using
vias close to the capacitor terminal. Connect SGND
of the device to the analog ground plane using a via
close to SGND. Lay the analog ground plane on the
inner layer, preferably next to the top layer. Use the
analog ground plane to cover the entire area under
critical signal components for the power converter.
2) Have a power ground plane for the switching-
converter power circuit under the power components
(input filter capacitor, output filter capacitor, inductor,
MOSFET, rectifier diode, and current-sense resis-
tor). Connect PGND to the power ground plane as
close to PGND as possible. Connect all other ground
connections to the power ground plane using vias
close to the terminals.
3) There are two loops in the power circuit that carry
high-frequency switching currents. One loop is when
the MOSFET is on (from the input filter capacitor
positive terminal, through the inductor, the internal
MOSFET, and the current-sense resistor, to the input
capacitor negative terminal). The other loop is when
the MOSFET is off (from the input capacitor positive
terminal, through the inductor, the rectifier diode,
output filter capacitor, to the input capacitor nega-
tive terminal). Analyze these two loops and make the
loop areas as small as possible. Wherever possible,
have a return path on the power ground plane for the
switching currents on the top layer copper traces, or
through power components. This reduces the loop
area considerably and provides a low-inductance
path for the switching currents. Reducing the loop
area also reduces radiation during switching.
4) Connect the power ground plane for the constant-
current LED driver part of the circuit to LEDGND as
close to the device as possible. Connect SGND to
PGND at the same point.
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