SC403MLTRT Semtech, SC403MLTRT Datasheet - Page 29

• Manufacturer Part Number: SC403MLTRT
• Manufacturer: Semtech

Specifications of SC403MLTRT

• Lead Free Status / Rohs Status: Supplier Unconfirmed

Applications Information (continued)
AGND Island
FB, VOUT, and Other Analog Control Signals
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AGND should have its own island of copper with
no other signal traces routed on this layer that
connects the AGND pins and pad of the device
to the analog control components.
All of the components for the analog control cir-
cuitry should be located so that the connections
to AGND are done by wide copper traces or vias
down to AGND.
Connect PGND to AGND with a short trace or 0Ω
resistor. This connection should be as close to
the device as possible.
The connection from the V
analog control circuitry must be routed from the
output capacitors and located on a quiet layer.
The traces between VOUT and the analog control
circuitry (VOUT, and FB pins) must be short and
routed away from noise sources, such as BST, LX,
VIN, and PGND between the input capacitors,
output capacitors, and the device.
ILIM and TON nodes must be as short as possible
to ensure the best accuracy in current limit and
on time.
R
to LX with a Kelvin trace to pin 28 on the device.
All of the LX pins are connected to the LX PAD
on the device, which should be a sufficient con-
nection and will prevent the need to connect
the resistor further into the LX plane.
The feedback components for the switcher and
the LDO need to be as close to the FB and FBL
pins of the device as possible to reduce the pos-
sibility of noise corrupting these analog signals.
ILIM
should be close to the device and connected
OUT
power to the
BST, ILIM and LX
Capacitors and Current Loops
Soft-Start Capacitor
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LX and BST are very noisy nodes and must be
routed to minimized the PCB area that is exposed
to these signals.
The connections for the boost capacitor
between the device and LX must be short and
directly connected to the LXBST (pin 13).
The connections for the current limit resistor
between the ILIM pin and LX must be as short as
possible and directly connected to pin 28 (LXS).
The LX node between the IC and the inductor
should be wide enough to handle the inductor
current and short enough to eliminate the pos-
sibility of LX noise corrupting other signals.
Multiple vias should be used to provide a good
connection to LX between the device and the
inductor.
The current loops between the input capacitors,
the device, the inductor, and the output capaci-
tors must be as close as possible to each other to
reduce IR drop across the copper.
All bypass and output capacitors must be con-
nected as close as possible to the pin on the
device.
The capacitor used for soft-start should be
located away from the BST pin and its capacitor.
If possible locate the boost capacitor on the
opposite side of the board form the IC and soft-
start capacitor.
SC403
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