MIC2870 Datasheet, PDF (22/25 Pages) Micrel Semiconductor – 1.5A Synchronous Boost Flash LED Driver with I2C Interface

Micrel, Inc.
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 ground (AGND) and power ground (PGND)
should be kept separate and connected at a single
location.
• The exposed pad (ePad) on the bottom of the IC must
be connected to the PGND ground plane of the PCB.
• 4 to 6 thermal vias must be placed on the PCB pad for
exposed pad and connected it to the PGND ground
plane to ensure a good PCB thermal resistance can be
achieved.
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.
MIC2870
Output Capacitor
• 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 LED1/LED2 pins.
• Make sure that the LED’s PCB land pattern can
provide sufficient PCB pad heat sink to the flash LED.
FRSET/TRSET Resistor
• The FRSET/TRSET resistor should be placed close to
the FRSET/TRSET pin and connected to AGND.
September 5, 2013
22
Revision 1.0