LM3677TL-1.8EV National Semiconductor, LM3677TL-1.8EV Datasheet - Page 20

• Manufacturer Part Number: LM3677TL-1.8EV
• Description: BOARD EVALUATION LM3677TL-1.8
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3677TL-1.8EV

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.8V
• Current - Output: 600mA
• Voltage - Input: 2.7 ~ 5.5V
• Regulator Topology: Buck
• Frequency - Switching: 3MHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM3677
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

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3.
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radiated noise. Special care must be given to place the
input filter capacitor very close to the V
Arrange the components so that the switching current
loops curl in the same direction. During the first half of
each cycle, current flows from the input filter capacitor,
through the LM3677 and inductor to the output filter
capacitor and back through ground, forming a current
loop. In the second half of each cycle, current is pulled
up from ground, through the LM3677 by the inductor, to
the output filter capacitor and then back through ground,
forming a second current loop. Routing these loops so
the current curls in the same direction prevents magnetic
field reversal between the two half-cycles and reduces
radiated noise.
Connect the ground pins of the LM3677, and filter
capacitors together using generous component-side
copper fill as a pseudo-ground plane. Then connect this
to the ground-plane (if one is used) with several vias. This
reduces ground-plane noise by preventing the switching
currents from circulating through the ground plane. It also
reduces ground bounce at the LM3677 by giving it a low-
impedance ground connection.
Use wide traces between the power components and for
power connections to the DC-DC converter circuit. This
IN
and GND pin.
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6.
7.
In mobile phones, for example, a common practice is to place
the DC-DC converter on one corner of the board, arrange the
CMOS digital circuitry around it (since this also generates
noise), and then place sensitive preamplifiers and IF stages
on the diagonally opposing corner. Often, the sensitive cir-
cuitry is shielded with a metal pan and power to it is post-
regulated to reduce conducted noise, using low-dropout
linear regulators.
reduces voltage errors caused by resistive losses across
the traces
Route noise sensitive traces such as the voltage
feedback path away from noisy traces between the
power components. The voltage feedback trace must
remain close to the LM3677 circuit and should be routed
directly from FB to V
should be routed opposite to noise components. This
reduces EMI radiated onto the DC-DC converter’s own
voltage feedback trace.
Place noise sensitive circuitry, such as radio IF blocks,
away from the DC-DC converter, CMOS digital blocks
and other noisy circuitry. Interference with noise-
sensitive circuitry in the system can be reduced through
distance.
OUT
at the output capacitor and