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参数资料
| 型号： | LTC3407IMSE-2#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1.6 A DUAL SWITCHING CONTROLLER, 2700 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | PLASTIC, MSOP-10 |
| 文件页数： | 4/16页 |
| 文件大小： | 227K |
| 代理商： | LTC3407IMSE-2#TR |
LTC3407-2
12
34072fb
APPLICATIONS INFORMATION
Design Example
As a design example, consider using the LTC3407-2 in
an portable application with a Li-Ion battery. The battery
provides a VIN = 2.8V to 4.2V. The load requires a maximum
of 800mA in active mode and 2mA in standby mode. The
output voltage is VOUT = 2.5V. Since the load still needs
power in standby, Burst Mode operation is selected for
good low load efciency.
First, calculate the inductor value for about 40% IOUT(MAX)
at maximum VIN:
L
≥
2.5V
2.25MHz 320mA
1–
2.5V
4.2V
= 1.4H
Choosing a vendor’s closest inductor value of 2.2μH,
results in a maximum ripple current of:
ΔI
L =
2.5V
2.25MHz 2.2H
1
2.5V
4.2V
= 204mA
For cost reasons, a ceramic capacitor will be used. COUT
selection is then based on load step droop instead of ESR
requirements. For a 5% output droop:
C
OUT ≈ 2.5
800mA
2.25MHz (5% 2.5V)
= 7.1μF
A good standard value is 10μF. Since the output impedance
of a Li-Ion battery is very low, CIN is typically 10μF.
The output voltage can now be programmed by choosing
the values of R1 and R2. To maintain high efciency, 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
in the layout diagram of Figure 3. Check the following in
your layout:
1. Does the capacitor CIN connect to the power VIN (Pin
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 COUT and L1 closely connected? The (–) plate of
COUT returns current to GND and the (–) plate of CIN.
3. The resistor divider, R1 and R2, must be connected
between the (+) plate of COUT and a ground sense line
terminated near GND (Exposed Pad). The feedback
signals VFB should be routed away from noisy compo-
nents and 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 CIN and the resistors R1 to R4 should be
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
CIN or COUT.
6. Flood all unused areas on all layers with copper. Flooding
with copper will reduce the temperature rise of power
components. These copper areas should be connected
to VIN or GND.
Figure 3. LTC3407-2 Layout Diagram (See Board
Layout Checklist)
RUN2
VIN
VOUT2
VOUT1
RUN1
POR
SW1
VFB1
GND
VFB2
SW2
MODE/SYNC
LTC3407-2
CIN
C4
C5
L1
L2
R4
R2
R1
R3
COUT2
COUT1
3407 F03
BOLD LINES INDICATE HIGH CURRENT PATHS
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