LT1613CS5 데이터 시트보기 (PDF) - Linear Technology
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LT1613CS5 Datasheet PDF : 12 Pages
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OPERATIO
LAYOUT
The LT1613 switches current at high speed, mandating
careful attention to layout for proper performance. You
will not get advertised performance with careless layouts.
Figure 2 shows recommended component placement for
a boost (step-up) converter. Follow this closely in your
PCB layout. Note the direct path of the switching loops.
Input capacitor C1 must be placed close (< 5mm) to the IC
package. As little as 10mm of wire or PC trace from CIN to
VIN will cause problems such as inability to regulate or
oscillation.
The ground terminal of output capacitor C2 should tie
close to Pin 2 of the LT1613. Doing this reduces dI/dt in the
ground copper which keeps high frequency spikes to a
minimum. The DC/DC converter ground should tie to the
PC board ground plane at one place only, to avoid intro-
ducing dI/dt in the ground plane.
A SEPIC (single-ended primary inductance converter)
schematic is shown in Figure 3. This converter topology
produces a regulated output voltage that spans (i.e., can
be higher or lower than) the output. Recommended com-
ponent placement for a SEPIC is shown in Figure 4.
LT1613
VIN
4V TO
7V
+
C1
15µF
SHDN
L1A
22µH
VIN
SW
LT1613
SHDN
FB
GND
C3
1µF
R1
100k
R2
32.4k
L1B
22µH
D1
VOUT
+
5V/150mA
C2
15µF
C1, C2: AVX TAJA156M016
C3: TAIYO YUDEN JMK325BJ226MM
D1: MOTOROLA MBR0520
L1, L2: MURATA LQH3C220
1613 F03
Figure 3. Single-Ended Primary Inductance Converter (SEPIC)
Generates 5V from An Input Voltage Above or Below 5V
L1B
VOUT
D1
C3
+
C2
VIAS TO
GROUND
PLANE
L1A
+
C1
1
5
2
3
4
R2
VIN
SHUTDOWN
VOUT
D1
+
C2
VIAS TO
GROUND
PLANE
L1
+
C1
VIN
1
5
2
3
4
SHUTDOWN
R2
GROUND
R1
1613 F02
Figure 2. Recommended Component Placement for Boost
Converter. Note Direct High Current Paths Using Wide PCB
Traces. Minimize Area at Pin 3 (FB). Use Vias to Tie Local
Ground Into System Ground Plane. Use Vias at Location Shown
to Avoid Introducing Switching Currents Into Ground Plane
GROUND
R1
1613 F04
Figure 4. Recommended Component Placement for SEPIC
COMPONENT SELECTION
Inductors
Inductors used with the LT1613 should have a saturation
current rating (where inductance is approximately 70% of
zero current inductance) of approximately 0.5A or greater.
DCR of the inductors should be 0.5Ω or less. For boost
converters, inductance should be 4.7µH for input voltage
less than 3.3V and 10µH for inputs above 3.3V. When
using the device as a SEPIC, either a coupled inductor or
two separate inductors can be used. If using separate
inductors, 22µH units are recommended for input voltage
above 3.3V. Coupled inductors have a beneficial mutual
inductance, so a 10µH coupled inductor results in the
same ripple current as two 20µH uncoupled units.
5
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