Rainbow Electronics MAX16841 - Manual (Page 13)

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MAX16841
Controller IC for Dimmable Offline LED Lamps
Layout Recommendations
Careful PCB layout is critical to achieve low switching
losses, and clean, stable operation. The switching-
converter portion 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) Ensure that all heat-dissipating components have
adequate cooling.
2) Isolate the power components and high-current paths
from the sensitive analog circuitry.
3) Have a power ground plane for the switching-
converter power circuit under the power compo-
nents (input filter capacitor, output filter capacitor,
inductor, MOSFET, rectifier diode, and current-sense
resistor). Connect GND to the power ground plane as
close as possible to GND. Connect all other ground
connections to the power ground plane using vias
close to the terminals
4) 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 posi-
tive terminal, through the output capacitor, inductor,
switching MOSFET, and current-sense resistor, to the
input capacitor negative terminal). The other loop is
when the MOSFET is off (from the output capacitor
negative terminal, through the inductor, the rectifier
diode, and output filter capacitor positive 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 con-
siderably and provides a low-inductance path for
the switching currents. Reducing the loop area also
reduces radiation during switching.