LM2734YMKX National Semiconductor, LM2734YMKX Datasheet - Page 11

• Manufacturer Part Number: LM2734YMKX
• Description: IC,SMPS CONTROLLER,CURRENT-MODE,BICMOS,TSOP,6PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM2734YMKX

• Rohs Compliant: NO

PCB Layout Considerations
When planning layout there are a few things to consider when
trying to achieve a clean, regulated output. The most impor-
tant consideration when completing the layout is the close
coupling of the GND connections of the C
catch diode D1. These ground ends should be close to one
another and be connected to the GND plane with at least two
through-holes. Place these components as close to the IC as
possible. Next in importance is the location of the GND con-
nection of the C
connections of C
There should be a continuous ground plane on the bottom
layer of a two-layer board except under the switching node
island.
OUT
IN
and D1.
capacitor, which should be near the GND
IN
capacitor and the
11
The FB pin is a high impedance node and care should be
taken to make the FB trace short to avoid noise pickup and
inaccurate regulation. The feedback resistors should be
placed as close as possible to the IC, with the GND of R2
placed as close as possible to the GND of the IC. The V
trace to R1 should be routed away from the inductor and any
other traces that are switching.
High AC currents flow through the V
so they should be as short and wide as possible. However,
making the traces wide increases radiated noise, so the de-
signer must make this trade-off. Radiated noise can be de-
creased by choosing a shielded inductor.
The remaining components should also be placed as close
as possible to the IC. Please see Application Note AN-1229
for further considerations and the LM2734 demo board as an
example of a four-layer layout.
IN
, SW and V
www.national.com
OUT
traces,
OUT