SC4518HEVB-2 Semtech, SC4518HEVB-2 Datasheet - Page 11

• Manufacturer Part Number: SC4518HEVB-2
• Description: EVALUATION BOARD
• Manufacturer: Semtech

Specifications of SC4518HEVB-2

• Silicon Manufacturer: Semtech
• Application Sub Type: Step Down Switching Regulator
• Kit Application Type: Power Management - Voltage Regulator
• Silicon Core Number: SC4518H
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Where:
One integrator is added at origin to increase the DC gain.
loop gain has –20dB/dec rate when it reaches 0dB line.
frequency switching noises. Figure 4 gives the asymptotic
diagrams of the power stage with current loop closed
and its loop gain.
Figure 4. Asymptotic diagrams of power stage with
current loop closed and its loop gain.
The design guidelines for the SC4518H applications are
as following:
1. Set the loop gain crossover corner frequency
2. Place an integrator at the origin to increase DC and
3. Select
4. Place a high frequency compensator pole
POWER MANAGEMENT
Application Information (Cont.)
Z
P2
2007 Semtech Corp.
is used to cancel the power stage pole
for given switching corner frequency
low frequency gains.
-20dB/dec rate to go across the 0dB line.
the switching ripple and high frequency noise with
the adequate phase lag at
is placed at half switching frequency to reject high
Mag
P2
(
P2
= f
Z
such that it is placed at
s
) to get the maximum attenuation of
ω
ω
p1
Z
p
1
R
L
1
C
C.
Loop gain T(s)
ω
C
Power stage
P1
to obtain a
C
P1
= 2 f
ω
so that the
P2
c
.
C
11
Layout Guidelines:
In order to achieve optimal electrical and thermal
performance for high frequency converters, special
attention must be paid to the PCB layouts. The goal of
layout optimization is to identify the high di/dt loops and
minimize them. The following guidelines should be used
to ensure proper operation of the converters.
1. A ground plane is suggested to minimize switching
2. Start the PCB layout by placing the power components
3. The V
4. The trace connecting the feedback resistors to the
5. Minimize the loop including input capacitor, the
6. Maximize the trace width of the loop connecting the
7.
8. Connect Pin 4 to a large copper area to remove the
noises and trace losses and maximize heat
transferring.
first. Arrange the power circuit to achieve a clean
power flow route. Put all power connections on one
side of the PCB with wide copper filled areas if
possible.
the V
output should be short, direct and far away from any
noise sources such as switching node and switching
components.
SC4518H and freewheeling diode D
passes high di/dt current. Make sure the trace width
is wide enough to reduce copper losses in this loop.
inductor, freewheeling diode D
capacitor.
compensation components directly to the GND pin
of the SC4518H by using a separate ground trace.
IC heat and increase the power capability of the
SC4518H. A few feedthrough holes are required to
connect this large copper area to a ground plane to
further improve the thermal environment of the
SC4518H. The traces attached to other pins should
be as wide as possible for the same purpose.
Connect the ground of the feedback divider and the
IN
IN
and GND pins.
bypass capacitor should be placed next to
2
SC4518H
and the output
www.semtech.com
2
. This loop