Datasheet

LM2734
V
IN
V
IN
EN
BOOST
SW
FB
GND
V
OUT
C3
L1
C2
R1
R2
D1
D2
ON
OFF
C1
R3
LM2734
www.ti.com SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
PCB Layout Considerations
When planning layout there are a few things to consider when trying to achieve a clean, regulated output. The
most important consideration when completing the layout is the close coupling of the GND connections of the C
IN
capacitor and the 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 connection of the C
OUT
capacitor, which should be near the GND
connections of C
IN
and D1.
There should be a continuous ground plane on the bottom layer of a two-layer board except under the switching
node island.
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
OUT
trace to R1 should be routed away from the
inductor and any other traces that are switching.
High AC currents flow through the V
IN
, SW and V
OUT
traces, so they should be as short and wide as possible.
However, making the traces wide increases radiated noise, so the designer must make this trade-off. Radiated
noise can be decreased 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 SNVA054 for further considerations and the LM2734 demo board as an example of a four-layer layout.
LM2734X Circuit Examples
Figure 27. LM2734X (1.6MHz)
V
BOOST
Derived from V
IN
5V to 1.5V/1A
Table 1. Bill of Materials for Figure 27
Part ID Part Value Part Number Manufacturer
U1 1A Buck Regulator LM2734X Texas Instruments
C1, Input Cap 10µF, 6.3V, X5R C3216X5ROJ106M TDK
C2, Output Cap 10µF, 6.3V, X5R C3216X5ROJ106M TDK
C3, Boost Cap 0.01uF, 16V, X7R C1005X7R1C103K TDK
D1, Catch Diode 0.3V
F
Schottky 1A, 10VR MBRM110L ON Semi
D2, Boost Diode 1V
F
@ 50mA Diode 1N4148W Diodes, Inc.
L1 4.7µH, 1.7A, VLCF4020T- 4R7N1R2 TDK
R1 8.87kΩ, 1% CRCW06038871F Vishay
R2 10.2kΩ, 1% CRCW06031022F Vishay
R3 100kΩ, 1% CRCW06031003F Vishay
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