LTC3417AIFE#TRPBF Linear Technology, LTC3417AIFE#TRPBF Datasheet - Page 16

• Manufacturer Part Number: LTC3417AIFE#TRPBF
• Description: IC DC/DC CONV DUAL 20TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3417AIFE#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 5 V
• Current - Output: 1A, 1.5A
• Frequency - Switching: 1.5MHz, 0.6MHz ~ 4MHz
• Voltage - Input: 2.25 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP Exposed Pad, 20-eTSSOP, 20-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
LTC3417A
Remembering that the above junction temperature is
obtained from an R
the junction temperature based on a higher R
it increases with temperature. However, we can safely as-
sume that the actual junction temperature will not exceed
the absolute maximum junction temperature of 125°C.
Design Example
As a design example, consider using the LTC3417A in
a portable application with a Li-Ion battery. The battery
provides a V
at 1.5A in active mode, and 1mA in standby mode. The
other load requires 2.5V at 1A in active mode, and 500μA
in standby mode. Since both loads still need power in
standby, Burst Mode operation is selected for good low
load effi ciency (SYNC/MODE = V
First, determine what frequency should be used. Higher
frequency results in a lower inductor value for a given ΔI
(ΔI
for wire wound surface mount inductors are usually in the
range of 1μH to 10μH.
Using the 1.5MHz frequency setting (FREQ = V
the following equations for L1 and L2:
16
CONVERTER OUTPUT
L1=
Use 1.5μH.
L2 =
Use 2.2μH.
L
is estimated as 0.35I
1.5MHz • 525mA
1.5MHz • 350mA
SW1
SW2
IN
1.8V
2.5V
from 2.8V to 4.2V. One load requires 1.8V
DS(ON)
LOAD(MAX)
at 25°C, we might recalculate
1–
1–
I
LOAD(MAX)
1.5A
1.8V
1A
4.2V
2.5V
4.2V
IN
).
). Reasonable values
= 1.3μH
= 1.9μH
DS(ON)
525mA
350mA
IN
ΔI
), we get
L
since
L
C
requirements. For a 2.5% output droop:
The closest standard values are 47μF and 22μF .
The output voltages can now be programmed by choos-
ing the values of R1, R2, R3, and R4. To maintain high
effi ciency, the current in these resistors should be kept
small. Choosing 2μA with the 0.8V feedback voltages makes
R2 and R4 equal to 400k. A close standard 1% resistor is
412k. This then makes R1 = 515k. A close standard 1%
is 511k. Similarily, with R4 at 412k, R3 is equal to 875k.
A close 1% resistor is 866k.
The compensation should be optimized for these com-
ponents by examining the load step response, but a
good place to start for the LTC3417A is with a 5.9kΩ and
2200pF fi lter on I
output capacitor may need to be increased depending on
the actual undershoot during a load step.
The PGOOD pin is a common drain output and requires a
pull-up resistor. A 100k resistor is used for adequate speed.
Figure 4 shows a complete schematic for this design.
OUT
C
C
OUT1
OUT2
selection is based on load step droop instead of ESR
= 2.5 •
= 2.5 •
1.5MHz 5% • 1.8V
1.5MHz 5% • 2.5V
TH1
and 2.87k and 6800pF on I
1.5A
(
(
1A
)
)
= 28μF
= 13μF
TH2
. The
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