MIC2874YCS datasheet(19/22 Pages) MICREL

19 / 22 page

Micrel, Inc.

MIC2874

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.

August 26, 2014

Revision 1.0

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