LTC3407EDD-3#TRPBF Linear Technology, LTC3407EDD-3#TRPBF Datasheet - Page 8

• Manufacturer Part Number: LTC3407EDD-3#TRPBF
• Description: IC REG DC/DC DUAL STEPDOWN 10DFN
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3407EDD-3#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 5 V
• Current - Output: 1A
• Frequency - Switching: 1.5MHz
• Voltage - Input: 2.5 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
LTC3407-3
A general LTC3407-3 application circuit is shown in
Figure 2. External component selection is driven by the
load requirement, and begins with the selection of the
inductor L. Once the inductor is chosen, C
can be selected.
Inductor Selection
Although the inductor does not infl uence 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 ΔI
0.3 • I
largest ripple current ΔI
voltage. To guarantee that the ripple current stays below a
specifi ed maximum, the inductor value should be chosen
according to the following equation:
The inductor value will also have an effect on Burst Mode
operation. The transition from low current operation
begins when the peak inductor current falls below a level
set by the burst clamp. Lower inductor values result in
higher ripple current which causes this to occur at lower
load currents. This causes a dip in effi ciency 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 materials are
small and don’t radiate much energy, but generally cost
more than powdered iron core inductors with similar elec-
trical characteristics. The choice of which style inductor
to use often depends more on the price vs size require-
ments and any radiated fi eld/EMI requirements than on
8
OUT
L
:
I
L
LIM
f
=
O
V
, where I
OUT
• I
V
f
O
OUT
• L
L
• 1–
• 1–
LIM
V
V
is the peak switch current limit. The
IN(MAX)
V
V
OUT
IN
OUT
L
occurs at the maximum input
L
allows the use of low
IN
L
decreases
and C
IN
OUT
L
or
=
what the LTC3407-3 requires to operate. Table 1 shows
some typical surface mount inductors that work well in
LTC3407-3 applications.
Table 1. Representative Surface Mount Inductors
PART
NUMBER
Sumida
CDRH3D16
Sumida
CDRH2D11
Sumida
CMD4D11
Murata
LQH32CN
Toko
D312F
Panasonic
ELT5KT
Input Capacitor (C
In continuous mode, the input current of the converter is a
square wave with a duty cycle of approximately V
To prevent large voltage transients, a low equivalent series
resistance (ESR) input capacitor sized for the maximum
RMS current must be used. The maximum RMS capacitor
current is given by:
where the maximum average output current I
the peak current minus half the peak-to-peak ripple cur-
rent, I
This formula has a maximum at V
= I
design because even signifi cant deviations do not offer
much relief. Note that capacitor manufacturer’s ripple cur-
rent ratings are often based on only 2000 hours lifetime.
This makes it advisable to further derate the capacitor,
or choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to meet
the size or height requirements of the design. An additional
0.1μF to 1μF ceramic capacitor is also recommended on
V
ceramic capacitor solution.
IN
I
OUT
RMS
for high frequency decoupling, when not using an all
MAX
/2. This simple worst-case is commonly used to
≈I
MAX
= I
VALUE
(μH)
2.2
3.3
4.7
1.5
2.2
2.2
3.3
1.0
2.2
2.2
3.3
3.3
4.7
LIM
– ΔI
V
OUT
IN
(Ω MAX)
0.075
0.110
0.162
0.068
0.170
0.116
0.174
0.060
0.097
0.060
0.260
) Selection
DCR
0.17
0.20
L
/2.
(V
V
IN
IN
– V
CURRENT (A)
OUT
MAX DC
0.900
0.780
0.950
0.770
1.20
1.10
0.90
1.00
0.79
1.08
0.92
1.00
0.95
IN
)
= 2V
OUT
W × L × H (mm
3.8 × 3.8 × 1.8
3.2 × 3.2 × 1.2
4.4 × 5.8 × 1.2
2.5 × 3.2 × 2.0
2.5 × 3.2 × 2.0
4.5 × 5.4 × 1.2
, where I
MAX
SIZE
OUT
equals
34073fb
/V
RMS
3
IN
)
.