LTC3407EDD-3#PBF Linear Technology, LTC3407EDD-3#PBF Datasheet - Page 9

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

Specifications of LTC3407EDD-3#PBF

• 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
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 ,
Panasonic Special Polymer (SP), and Kemet A700, of-
fer very low ESR, but have a lower capacitance density
than other types. Tantalum capacitors have the highest
capacitance density, but they have a larger ESR and it
is critical that the capacitors are surge tested for use in
switching power supplies. An excellent choice is the AVX
TPS series of surface mount tantalums, available in case
heights ranging from 2mm to 4mm. Aluminum electrolytic
capacitors have a signifi cantly larger ESR, and are often
used in extremely cost-sensitive applications provided that
consideration is given to ripple current ratings and long
term reliability. Ceramic capacitors have the lowest ESR
and cost, but also have the lowest capacitance density,
a high voltage and temperature coeffi cient, and exhibit
audible piezoelectric effects. In addition, the high Q of
ESR
V
OUT
L
COUT
= ripple current in the inductor. The output ripple
< 150mΩ
I
L
ESR+
OUT
OUT
is driven by the required ESR to
8f
) Selection
O
L
C
1
= 0.3 • I
OUT
OUT
OUT
= output capacitance
LIM
IN
have been met, the
and f
the output ripple
O
L
= 2.25MHz
RIPPLE(P-P)
increases
OUT
) is
ceramic capacitors along with trace inductance can lead
to signifi cant ringing.
In most cases, 0.1μF to 1μF of ceramic capacitors should
also be placed close to the LTC3407-3 in parallel with the
main capacitors for high frequency decoupling.
Ceramic Input and Output Capacitors
Higher value, lower cost ceramic capacitors are now be-
coming available in smaller case sizes. These are tempting
for switching regulator use because of their very low ESR.
Unfortunately, the ESR is so low that it can cause loop
stability problems. Solid tantalum capacitor ESR generates
a loop “zero” at 5kHz to 50kHz that is instrumental in giving
acceptable loop phase margin. Ceramic capacitors remain
capacitive to beyond 300kHz and usually resonate with their
ESL before ESR becomes effective. Also, ceramic caps are
prone to temperature effects which requires the designer
to check loop stability over the operating temperature
range. To minimize their large temperature and voltage
coeffi cients, only X5R or X7R ceramic capacitors should
be used. A good selection of ceramic capacitors is available
from Taiyo Yuden, AVX, Kemet, TDK, and Murata.
Great care must be taken when using only ceramic input
and output capacitors. When a ceramic capacitor is used
at the input and the power is being supplied through long
wires, such as from a wall adapter, a load step at the output
can induce ringing at the V
couple to the output and be mistaken as loop instability.
At worst, the ringing at the input can be large enough to
damage the part.
V
OUT2
V
IN
Figure 2. LTC3407-3 General Schematic
C
OUT2
L2 μH
10μF
MODE/SYNC
SW2
V
RUN2
OUT2
LTC3407-3
GND
V
IN
IN
pin. At best, this ringing can
RUN1
V
SW1
POR
OUT1
LTC3407-3
L1 μH
100k
RESET
34073 F02
C
V
OUT1
OUT1
34073fb
9