LTC3619B Linear Technology, LTC3619B Datasheet - Page 11

• Manufacturer Part Number: LTC3619B
• Description: 400mA/800mA Synchronous Step-Down DC/DC
• Manufacturer: Linear Technology

applicaTions inForMaTion
A general LTC3619B application circuit is shown in Figure 2.
External component selection is driven by the load require-
ment, and begins with the selection of the inductor L. Once
the inductor is chosen, C
Inductor Selection
Although the inductor does not influence the operat-
ing frequency, the inductor value has a direct effect on
ripple current. The inductor ripple current ΔI
with higher inductance and increases with higher V
V
Accepting larger values of ΔI
inductances, but results in higher output voltage ripple,
greater core losses, and lower output current capability.
A reasonable starting point for setting ripple current is
40% of the maximum output load current. So, for a 800mA
regulator, ΔI
The inductor value will also have an effect on Burst Mode
operation. The transition to low current operation begins
when the peak inductor current falls below a level set by
the internal burst clamp. Lower inductor values result in
higher ripple current which causes the transition to occur
at lower load currents. This causes a dip in efficiency in
the upper range of low current operation. Furthermore,
lower inductance values will cause the bursts to occur
with increased frequency.
V
2.5V TO 5.5V
OUT2
OUT
ΔI
:
L
V
=
IN
C
V
f
OUT2
O
OUT
Figure 2. LTC3619B General Schematic
• L
L
= 320mA (40% of 800mA).
• 1−
C
R4
F2

 
C1
L2
R3
V
V
OUT
IN
PGOOD2
RUN2
SW2
V
RLIM
FB2
IN
LTC3619B

 
C
and C
LIM
V
IN
PGOOD1
L
GND
RUN1
R
SW1
V
LIM
OUT
allows the use of low
FB1
can be selected.
R1
L1
C
R2
F1
L
decreases
IN
(1)
C
or
3619B F02
V
OUT1
OUT1
Inductor Core Selection
Different core materials and shapes will change the size/cur-
rent and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or permalloy materials are
small and do not radiate much energy, but generally cost
more than powdered iron core inductors with similar
electrical characteristics. The choice of which style induc-
tor to use often depends more on the price versus size
requirements, and any radiated field/EMI requirements,
than on what the LTC3619B requires to operate. Table 1
shows some typical surface mount inductors that work
well in LTC3619B applications.
Table 1. Representative Surface Mount Inductors
Taiyo Yuden CB2016T2R2M
FACTURER
Panasonic
Coilcraft
Sumida
MANU-
Murata
TDK
FDK
LPS4012-152ML
LPS4012-222ML
LPS4012-332ML
LPS4012-472ML
LPS4018-222ML
LPS4018-332ML
LPS4018-472ML
FDKMIPF2520D
FDKMIPF2520D
FDKMIPF2520D
LQH32CN4R7M23 4.7µH
ELT5KT4R7M
CDRH2D18/LD
CDH38D11SNP-
3R3M
CDH38D11SNP-
2R2M
CB2012T2R2M
CB2016T3R3M
NR30102R2M
NR30104R7M
VLF3010AT4R7-
MR70
VLF3010AT3R3-
MR87
VLF3010AT2R2-
M1R0
VLF4012AT-2R2
M1R5
VLF5012ST-3R3
M1R7
VLF5014ST-2R2
M2R3
PART NUMBER
VALUE
1.5µH
2.2µH
3.3µH
4.7µH
2.2µH
3.3µH
4.7µH
4.7µH
3.3µH
2.2µH
4.7µH
4.7µH
3.3μH
2.2μH
2.2µH
2.2µH
3.3µH
2.2µH
4.7µH
4.7µH
3.3µH
2.2µH
2.2µH
3.3μH
2.2µH
CURRENT
MAX DC
2200mA
1750mA
1450mA
1450mA
2300mA
2000mA
1800mA
1100mA
1200mA
1300mA
1560mA
1900mA
1100mA
1000mA
1500mA
1700mA
2300mA
450mA
950mA
630mA
510mA
530mA
410mA
750mA
700mA
870mA
LTC3619B
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0.070Ω
0.100Ω
0.100Ω
0.170Ω
0.070Ω
0.080Ω
0.125Ω
0.086Ω
0.115Ω
0.082Ω
0.076Ω
0.095Ω
0.059Ω
0.11Ω
0.08Ω
0.13Ω
0.33Ω
0.27Ω
0.19Ω
0.28Ω
0.17Ω
0.12Ω
0.1Ω
0.2Ω
0.2Ω
0.1Ω
DCR

1.25mm
HEIGHT
1.2mm
1.2mm
1.2mm
1.2mm
1.8mm
1.8mm
1.8mm
1.2mm
1.2mm
1.2mm
1.6mm
1.6mm
1.2mm
1.2mm
1.4mm
1mm
1mm
1mm
2mm
2mm
1mm
1mm
1mm
1mm
1mm
3619bfa