Datasheet

9
LTC3564
3564f
The basic LTC3564 application circuit is shown in Figure 1.
External component selection is driven by the load require-
ment and begins with the selection of L followed by C
IN
and
C
OUT
.
Inductor Selection
For most applications, the value of the inductor will fall in
the range of 0.47μH to 2.2μH. Its value is chosen based on
the desired ripple current. Large value inductors lower
ripple current and small value inductors result in higher
ripple currents. Higher V
IN
or V
OUT
also increases the ripple
current as shown in equation 1. A reasonable starting point
for setting ripple current is ΔI
L
= 500mA (40% of 1.25A).
Δ =
()( )
−
⎛
⎝
⎜
⎞
⎠
⎟
I
fL
V
V
V
L OUT
OUT
IN
1
1
(1)
The DC current rating of the inductor should be at least
equal to the maximum load current plus half the ripple
current to prevent core saturation. Thus, a 1.5A rated
inductor should be enough for most applications (1.25A
+ 250mA). For better efficiency, choose a low DC-resis-
tance inductor.
The inductor value also has an effect on Burst Mode
operation. The transition to low current operation begins
when the inductor current peaks fall to approximately
300mA. Lower inductor values (higher ΔI
L
) will cause this
to occur at lower load currents, which can cause a dip in
efficiency in the upper range of low current operation. In
Burst Mode operation, lower inductance values will cause
the burst frequency to increase.
Inductor Core Selection
Different core materials and shapes will change the size/
current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy mate-
rials are small and don’t radiate much energy, but gener-
ally cost more than powdered iron core inductors with
similar electrical characteristics. The choice of which style
inductor to use often depends more on the price vs size
requirements and any radiated field/EMI requirements
than on what the LTC3564 requires to operate. Table 1
shows some typical surface mount inductors that work
well in LTC3564 applications.
APPLICATIO S I FOR ATIO
WUU
U
Table 1. Representative Surface Mount Inductors
MANUFATURER PART NUMBER VALUE (μH) MAX DC CURRENT (A) DCR (mΩ) HEIGHT (mm)
Toko A915AY-1R1M-DC53LC 1.1 3.25 16 3
1070AS-1R0N-DB3020C 1 1.9 47 2
Sumida CDRH4D18C/LD-1R1 1.1 2.1 24 2
CDRH3D14-1R2 1.2 2.2 36 1.5
CR5D11-1R0 1 2.2 40 1.2
CDRH2D18/HP-2R2 2.2 1.6 48 2
FDK MIPW3226D0R9M 0.9 1.4 70 1
Coilcraft LPO6610-122ML 1.2 2.1 80 1
LPS4018-222ML 2.2 2.5 70 1.8
Vishay IHLP1616ABERR47M01 0.47 5 20 1.2
IHLP1616ABER1R0M01 1 4 45 1.2
V
IN
LTC3564
RUN
R1
3564 F01
R2
C
F
L
C
IN
C
OUT
SW
V
IN
V
OUT
V
FB
GND
Figure 1. LTC3564 General Schematic