MIC3201 datasheet(10/16 Pages) MICREL

10 / 16 page

Micrel, Inc.

MIC3201

February 2011

M9999-021011-B

PCB Layout Guideline

Warning!!! To minimize EMI and output noise, follow

these layout recommendations.

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 insure

proper operation of the MIC3201 regulator.

Use fat traces to route the input and output power lines.

The exposed pad (EP) on the bottom of the IC must be

connected to the ground.

Use four via to connect the EP to the ground plane.

Signal and power grounds should be kept separate and

connected at only one location.

Input Capacitor

Place the input capacitors on the same side of the board

and as close to the IC as possible.

Keep both the VIN and PGND connections short.

Place several vias to the ground plane close to the input

capacitor ground terminal, but not between the input

capacitors and IC pins.

Use either X7R or X5R dielectric input capacitors. Do not

use Y5V or Z5U type capacitors.

Do not replace the ceramic input capacitor with any

other type of capacitor. Any type of capacitor can be

placed in parallel with the input capacitor.

If a Tantalum input capacitor is placed in parallel with the

input capacitor, it must be recommended for switching

regulator applications and the operating voltage must be

derated by 50%.

In “Hot-Plug” applications, a Tantalum or Electrolytic

bypass capacitor must be placed in parallel to ceramic

capacitor to limit the over-voltage spike seen on the

input supply with power is suddenly applied. In this case,

an additional Tantalum or Electrolytic bypass input

capacitor of 22µF or higher is required at the input power

connection if necessary.

Inductor

Keep the inductor connection to the switch node (LX)

short.

Do not route any digital lines underneath or close to the

inductor.

To minimize noise, place a ground plane underneath the

inductor.

Output Capacitor

If LED ripple current needs to be reduced then place a 10µF

capacitor across LED. The capacitor must be placed as

close to the LED as possible.

Diode

Place the Schottky diode on the same side of the board as

the IC and input capacitor.

The connection from the Schottky diode’s Anode to the IC

LX pin must be as short as possible.

The diode’s Cathode connection to the RCS must be keep as

short as possible.

RC Snubber

If a RC snubber is needed, place the RC snubber on the

same side of the board and as close to the Schottky diode

as possible.

RCS (Current Sense Resistor)

VIN pin and CS pin must be as close as possible to RCS.

Make a Kelvin connection to the VIN and CS pin respectively

for current sensing.

Trace Routing Recommendation

Keep the power traces as short and wide as possible. One

current flowing loop is during the MOSFET ON time, the

traces connecting the input capacitor CIN, RCS, LEDs,

Inductor, the MIC3201 LX and PGND pin and back to CIN.

The other current flowing loop is during the MOSFET OFF

time, the traces connecting RCS, LED, inductor, free wheeling

diode and back to RCS. These two loop areas should kept as

small as possible to minimize the noise interference,

Keep all analog signal traces away from the LX pin and its

connecting traces.

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