MIC3201_11 Datasheet, PDF (10/16 Pages) Micrel Semiconductor – High Brightness LED Driver with High-Side Current Sense

Micrel, Inc.
MIC3201
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.
IC
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 R_CS 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.
R_CS (Current Sense Resistor)
VIN pin and CS pin must be as close as possible to R_CS.
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 C_IN, R_CS, LEDs,
Inductor, the MIC3201 LX and PGND pin and back to C_IN.
The other current flowing loop is during the MOSFET OFF
time, the traces connecting R_CS, LED, inductor, free wheeling
diode and back to R_CS. 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.
February 2011
10
M9999-021011-B