LTC3407EDD-2 Linear Technology, LTC3407EDD-2 Datasheet - Page 12

• Manufacturer Part Number: LTC3407EDD-2
• Description: IC REG DC/DC DUAL STEPDOWN 10DFN
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3407EDD-2

• 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: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIONS INFORMATION
LTC3407-2
Design Example
As a design example, consider using the LTC3407-2 in
an portable application with a Li-Ion battery. The battery
provides a V
of 800mA 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 40% I
at maximum V
Choosing a vendor’s closest inductor value of 2.2μH,
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:
A good standard value is 10μF . Since the output impedance
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.
Board Layout Considerations
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3407-2. These items are also illustrated graphically
12
L
C
OUT
I
L
2.25MHz • 320mA
=
≈ 2.5
2.25MHz • 2.2µH
IN
2.5V
= 2.8V to 4.2V. The load requires a maximum
2.25MHz • (5% • 2.5V)
IN
2.5V
:
OUT
800mA
= 2.5V. Since the load still needs
• 1–
• 1
2.5V
4.2V
IN
2.5V
4.2V
is typically 10μF .
= 7.1μF
=1.4µH
= 204mA
OUT(MAX)
OUT
in the layout diagram of Figure 3. Check the following in
your layout:
1. Does the capacitor C
2. Are the C
3. The resistor divider, R1 and R2, must be connected
4. Keep sensitive components away from the SW pins. The
5. A ground plane is preferred, but if not available, keep
6. Flood all unused areas on all layers with copper. Flooding
V
BOLD LINES INDICATE HIGH CURRENT PATHS
OUT2
3) and GND (Exposed Pad) as close as possible? This
capacitor provides the AC current to the internal power
MOSFETs and their drivers.
C
between the (+) plate of C
terminated near GND (Exposed Pad). The feedback
signals V
nents and traces, such as the SW line (Pins 4 and 7),
and its trace should be minimized.
input capacitor C
routed away from the SW traces and the inductors.
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
with copper will reduce the temperature rise of power
components. These copper areas should be connected
to V
OUT
IN
or C
IN
Figure 3. LTC3407-2 Layout Diagram (See Board
Layout Checklist)
C
OUT2
returns current to GND and the (–) plate of C
or GND.
OUT
OUT
V
R4
C5
FB
IN
.
should be routed away from noisy compo-
and L1 closely connected? The (–) plate of
C
IN
IN
R3
L2
and the resistors R1 to R4 should be
IN
MODE/SYNC
SW2
V
RUN2
FB2
connect to the power V
LTC3407-2
OUT
GND
V
IN
and a ground sense line
RUN1
SW1
POR
V
FB1
R1
L1
C4
R2
3407 F03
IN
34072fc
(Pin
C
IN
V
OUT1
OUT1
.