LTC3407EMSE Linear Technology, LTC3407EMSE Datasheet - Page 12

• Manufacturer Part Number: LTC3407EMSE
• Description: IC REG DC/DC DUAL 1.5MHZ 10-MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3407EMSE

• 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-MSOP Exposed Pad, 10-HMSOP, 10-eMSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIONS INFORMATION
LTC3407
the regulator operating in a 70°C ambient temperature is
approximately:
which is below the absolute maximum junction tempera-
ture of 125°C.
Design Example
As a design example, consider using the LTC3407 in an
portable application with a Li-Ion battery. The battery pro-
vides a V
of 600mA in active mode and 2mA in standby mode. The
output voltage is V
power in standby, Burst Mode operation is selected for
good low load effi ciency.
First, calculate the inductor value for about 30% ripple
current at maximum V
Choosing the closest inductor from a vendor of 2.2μH
inductor, results in a maximum ripple current of:
For cost reasons, a ceramic capacitor will be used. C
selection is then based on load step droop instead of ESR
requirements. For a 5% output droop:
The closest standard value is 10μF . Since the output imped-
ance of a Li-Ion battery is very low, C
The output voltage can now be programmed by choosing
the values of R1 and R2. To maintain high effi ciency, the
current in these resistors should be kept small. Choosing
2μA with the 0.6V feedback voltage makes R1~300k. A close
standard 1% resistor is 280k, and R2 is then 887k.
The POR pin is a common drain output and requires a pull-
up resistor. A 100k resistor is used for adequate speed.
Figure 1 shows the complete schematic for this design
example.
12
T
L ≥
C
ΔI
J
OUT
L
= 2 • 0.153 • 45 + 70 = 84°C
1.5MHz • 300mA
=
≈ 3
1.5MHz • 2.2μH
IN
= 2.8V to 4.2V. The load requires a maximum
1.5MHz • (5% • 2.5V)
2.5V
2.5V
OUT
600mA
IN
= 2.5V. Since the load still needs
:
• 1–
• 1−
⎛
⎜
⎝
⎛
⎜
⎝
2.5V
4.2V
2.5V
4.2V
= 9.6μF
⎞
⎟ = 2.25μH
⎠
⎞
⎟ = 307mA
⎠
IN
is typically 10μF .
OUT
Board Layout Considerations
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3407. These items are also illustrated graphically
in the layout diagram of Figure 3. Check the following in
your layout:
1. Does the capacitor C
3) and GND (exposed pad) as close as possible? This
capacitor provides the AC current to the internal power
MOSFETs and their drivers.
2. Are the C
C
3. The resistor divider, R1 and R2, must be connected
between the (+) plate of C
terminated near GND (Exposed Pad). The feedback signals
V
traces, such as the SW line (Pins 4 and 7), and its trace
should be minimized.
4. Keep sensitive components away from the SW pins. The
input capacitor C
routed away from the SW traces and the inductors.
5. A ground plane is preferred, but if not available, keep
the signal and power grounds segregated with small signal
components returning to the GND pin at one point and
should not share the high current path of C
6. Flood all unused areas on all layers with copper. Flood-
ing with copper will reduce the temperature rise of power
components. These copper areas should be connected to
V
V
BOLD LINES INDICATE HIGH CURRENT PATHS
Figure 3. LTC3407 Layout Diagram (See Board Layout Checklist)
OUT2
OUT
FB
IN
or GND.
should be routed away from noisy components and
returns current to GND and the (–) plate of C
C
OUT2
OUT
V
R4
C5
IN
and L1 closely connected? The (–) plate of
IN
C
IN
R3
and the resistors R1 to R4 should be
L2
IN
MODE/SYNC
SW2
V
RUN2
FB2
connect to the power V
OUT
LTC3407
GND
V
IN
and a ground sense line
RUN1
SW1
POR
V
FB1
R1
L1
IN
C4
R2
or C
3407 F03
IN
OUT
IN
.
(Pin
3407fa
C
.
V
OUT1
OUT1