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参数资料
| 型号： | LT3407EDD-2 |
| 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： | 3 X 3 MM, PLASTIC, MO-229WEED-2, DFN-10 |
| 文件页数： | 4/16页 |
| 文件大小： | 221K |
| 代理商： | LT3407EDD-2 |
LTC3407-2
12
34072fa
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
regulator operating in a 70
°C ambient temperature is
approximately:
TJ = 2 0.272 45 + 70 = 94.5°C
which is below the absolute maximum junction tempera-
ture of 125
°C.
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 maxi-
mum 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 efficiency.
First, calculate the inductor value for about 30% ripple
current at maximum VIN:
L
V
MHz
mA
V
H
=
=μ
25
2 25
300
1
25
42
15
.
–
.
Choosing a vendor’s closest inductor value of 2.2
μH,
results in a maximum ripple current of:
Δ=
μ
=
I
V
MHz
V
mA
L
25
225
2 2
1
25
42
204
.
. .
.
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
mA
MHz
V
F
OUT
≈=
μ
25
800
225
5
25
71
.
. ( % .
)
.
A good standard value is 10
μF. Since the output imped-
ance 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 efficiency, the
current in these resistors should be kept small. Choosing
2
μA with the 0.6V feedback voltage makes R1~300k. A
close standard 1% resistor is 280k, and R2 is then 887k.
The PGOOD 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 capaci-
tor 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 components 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 con-
nected to VIN or GND.
APPLICATIO S I FOR ATIO
WU
U
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