MAQ3203 Datasheet, PDF (16/23 Pages) Micrel Semiconductor – High-Brightness LED Driver Controller with High-Side Current Sense

Micrel, Inc.
MAQ3203
PCB Layout Guidelines
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 MAQ3203 regulator.
IC
Use thick traces to route the input and output power
lines.
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 traces as short as
possible.
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
(MOSFET drain) 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
4.7µF/50V capacitor across LED. The capacitor must be
placed as close to the LED as possible.
MOSFET
Place the MOSTET as close as possible to the MAQ3203 to
avoid the trace inductance. Provide sufficient copper area on
MOSFET ground to dissipate the heat.
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
switching node 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 MOSFET 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 switching node
and its connecting traces.
March 2011
16
M9999-032411-A