MIC2873 Datasheet, PDF (20/24 Pages) Micrel Semiconductor – 1.2A High-Brightness Flash LED Driver with Single-Wire Serial Interface

Micrel, Inc.
MIC2873
PCB Layout Guidelines
PCB layout is critical to achieve reliable, stable and
efficient performance. A ground plane is required to control
EMI and minimize the inductance in power, signal and
return paths. The following guidelines should be followed
to ensure proper operation of the device:
IC (Integrated Circuit)
• Place the IC close to the point-of-load (in this case, the
flash LED).
• Use fat traces to route the input and output power
lines.
• Analog grounds (LGND and AGND) and power ground
(PGND) should be kept separate and connected at a
single location.
• 6 to 12 thermal vias must be placed on the PCB top
layer PGND copper from the PGND pin and connected
it to the ground plane to ensure a good PCB thermal
resistance can be achieved.
• Since all the top copper areas connected directly to
the CSP package bumps are used as the immediate
PCB heat sink, these top copper areas should be
spread out from the bumps in funnel-shape to
maximize the top copper PCB heat sink areas.
VIN Decoupling Capacitor
• The VIN decoupling capacitor must be placed close to
the VIN pin of the IC and preferably connected directly
to the pin and not through any via. The capacitor must
be located right at the IC.
• The VIN decoupling capacitor should be connected to
analog ground (AGND).
• The VIN terminal is noise sensitive and the placement
of capacitor is very critical.
Inductor
• Keep both the inductor connections to the switch node
(SW) and input power line short and wide enough to
handle the switching current. Keep the areas of the
switching current loops small to minimize the EMI
problem.
• Do not route any digital lines underneath or close to
the inductor.
• Keep the switch node (SW) away from the noise
sensitive pins.
• To minimize noise, place a ground plane underneath
the inductor.
Output Capacitor
• The output capacitor must be placed close to the OUT
pin and PGND pin of the IC and preferably connected
directly and closely to the OUT pin and PGND pin
without going through any via to minimize the
switching current loop during the main switch off-cycle,
and the switching noise.
• Use wide and short traces to connect the output
capacitor to the OUT and PGND pins.
• Place several vias to the ground plane close to the
output capacitor ground terminal.
• Use either X5R or X7R temperature rating ceramic
capacitors. Do not use Y5V or Z5U type ceramic
capacitors.
Flash LED
• Use wide and short trace to connect the LED anode to
the OUT pin.
• Use wide and short trace to connect the LED cathode
to the LED pin.
• Make sure that the LED’s PCB land pattern can
provide sufficient PCB pad heat sink to the flash LED,
such as sufficient copper areas and thermal vias.
July 17, 2014
20
Revision 1.0