LTC3411EMS#TRPBF Linear Technology, LTC3411EMS#TRPBF Datasheet - Page 11

• Manufacturer Part Number: LTC3411EMS#TRPBF
• Description: IC CONV DC/DC SYNC STPDWN 10MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3411EMS#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 5 V
• Current - Output: 1.25A
• Frequency - Switching: 1MHz
• Voltage - Input: 2.63 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
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
to 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 recom-
mended on V
using an all ceramic capacitor solution.
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:
RMS
ESRC
Δ
V
= I
MAX
OUT
L
OUT
= ripple current in the inductor. The output ripple
OUT
= I
≈ Δ
/2. This simple worst case is commonly used
< 150mΩ
LIM
IN
I ESR
L
for high frequency decoupling, when not
⎛
⎜
⎝
– ΔI
OUT
OUT
L
/2.
+
is driven by the required ESR to
) Selection
8
f C
L
O OUT
= 0.3 • I
1
OUT
⎞
⎟
⎠
= output capacitance
LIM
IN
IN
the output ripple
= 2V
and f
OUT
L
MAX
O
increases
, where
= 1MHz
OUT
equals
) is
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 avail-
able from Sanyo has the lowest ESR(size) product of any
aluminum electrolytic at a somewhat higher price. Special
polymer capacitors, such as Sanyo POSCAP , offer very
low ESR, but have a lower capacitance density than other
types. Tantalum capacitors have the highest capacitance
density, but it has 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, avalable in case heights ranging
from 2mm to 4mm. Aluminum electrolytic capacitors have
a signifi cantly larger ESR, and is 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 ceramic capacitors along
with trace inductance can lead to signifi cant ringing. Other
capacitor types include the Panasonic specialty polymer
(SP) capacitors.
In most cases, 0.1μF to 1μF of ceramic capacitors should
also be placed close to the LTC3411 in parallel with the
main capacitors for high frequency decoupling.
OUT
have been met, the
LTC3411
RIPPLE(P-P)
11
3411fb