LM2736X EVAL National Semiconductor, LM2736X EVAL Datasheet - Page 11

• Manufacturer Part Number: LM2736X EVAL
• Description: BOARD EVALUATION LM2736X
• Manufacturer: National Semiconductor

Specifications of LM2736X EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.5V
• Current - Output: 750mA
• Voltage - Input: 3 ~ 18V
• Regulator Topology: Buck
• Frequency - Switching: 1.6MHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM2736
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -

Design Guide
OUTPUT VOLTAGE
The output voltage is set using the following equation where
R2 is connected between the FB pin and GND, and R1 is
connected between V
is 10kΩ.
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
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
O
and the FB pin. A good value for R2
(Continued)
IN
capacitor
11
GND connection of the C
near the GND 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.
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
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
for further considerations and the LM2736 demo board as an
example of a four-layer layout.
OUT
capacitor, which should be
IN
and D1.
IN
, SW and V
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OUT
traces,
OUT