LTC3407EDD-4#TRPBF Linear Technology, LTC3407EDD-4#TRPBF Datasheet - Page 8

• Manufacturer Part Number: LTC3407EDD-4#TRPBF
• Description: IC REG DC/DC DUAL STEPDOWN 10DFN
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3407EDD-4#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
LTC3407-4
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
what the LTC3407-4 requires to operate. Table 1 shows
some typical surface mount inductors that work well in
LTC3407-4 applications.
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.
8
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
LIM
– ΔI
V
OUT
IN
) Selection
L
/2.
(
V
V
IN
IN
– V
OUT
IN
)
= 2V
OUT
, where I
MAX
OUT
equals
/V
RMS
IN
.
Table 1. Representative Surface Mount Inductors
PART
NUMBER
Sumida
CDRH3D16
Sumida
CDRH2D11
Sumida
CMD4D11
Murata
LQH32CN
Toko
D312F
Panasonic
ELT5KT
Output Capacitor (C
The selection of C
minimize voltage ripple and load step transients. Typically,
once the ESR requirement is satisfi ed, the capacitance
is adequate for fi ltering. The output ripple (ΔV
determined by:
where f = operating frequency, C
and ΔI
is highest at maximum input voltage since ΔI
with input voltage. With ΔI
will be less than 100mV at maximum V
with:
Once the ESR requirements for C
RMS current rating generally far exceeds the I
requirement, except for an all ceramic solution.
In surface mount applications, multiple capacitors may
have to be paralleled to meet the capacitance, ESR or
RMS current handling requirement of the application.
Aluminum electrolytic, special polymer, ceramic and dry
tantulum capacitors are all available in surface mount
packages. The OS-CON semiconductor dielectric capacitor
available from Sanyo has the lowest ESR(size) product
of any aluminum electrolytic at a somewhat higher price.
Special polymer capacitors, such as Sanyo POSCAP ,
ESR
V
OUT
L
COUT
= ripple current in the inductor. The output ripple
VALUE
(μH)
< 150mΩ
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
I
L
ESR+
OUT
(Ω MAX)
OUT
0.075
0.110
0.162
0.068
0.170
0.116
0.174
0.060
0.097
0.060
0.260
DCR
0.17
0.20
is driven by the required ESR to
8f
) Selection
O
L
C
1
= 0.3 • I
CURRENT (A)
OUT
MAX DC
OUT
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
OUT
= output capacitance
LIM
IN
have been met, the
and f
the output ripple
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
O
L
= 2.25MHz
RIPPLE(P-P)
increases
SIZE
OUT
34074fa
) is
3
)