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LTC3544 Datasheet(PDF) 14 Page - Linear Technology

Part # LTC3544
Description  Quad Synchronous Step-Down Regulator
PDF  16 Pages
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Manufacturer  LINER [Linear Technology]
Direct Link  http://www.linear.com
Logo LINER - Linear Technology

LTC3544 Datasheet(HTML) 14 Page - Linear Technology

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LTC3544
14
3544fa
APPLICATIONS INFORMATION
Beginning with this channel, first calculate the inductor
value for about 35% ripple current (100mA in this example)
at maximum VIN. Using a form of Equation 1:
L
V
MHz
mA
V
V
µH
4
25
2 25
100
1
25
42
45
=
⎛
⎝⎜
⎞
⎠⎟
=
.
.•
–
.
.
.
For the inductor, use the closest standard value of 4.7μH.
A 4.7μF capacitor should be sufficient for the output ca-
pacitor. A larger output capacitor will attenuate the load
transient response, but increase the settling time. A value
for CIN = 4.7μF should suffice as the source impedance of
a Li-Ion battery is very low.
The feedback resistors program the output voltage.
Minimizing the current in these resistors will maximize
efficiency at very light loads, but totals on the order of
200k are a good compromise between efficiency and im-
munity to any adverse effects of PCB parasitic capacitance
on the feedback pins. Choosing 10μA with 0.8V feedback
voltage makes R7 = 80k. A close standard 1% resistor is
76.8k. Using:
R
V
Rk
OUT
8
08
1
7
163 2
= ⎛
⎝⎜
⎞
⎠⎟
=
.
–•
.
The closest standard 1% resistor is 162k. An optional
20pF feedback capacitor may be used to improve transient
response. The component values for the other channels
are chosen in a similar fashion.
Figure 5 shows the complete schematic for this example,
along with the efficiency curve and transient response for
the 300mA channel.
16
4
1
L2
4.7
μH
L1
10
μH
L4
4.7
μH
C6
20pF
C9
4.7
μF
C10
4.7
μF
C5
20pF
C8
20pF
C2
4.7
μF
C1
4.7
μF
VOUT1
1.2V
C4
10
μF
3544 F05a
VOUT2
2.5V
R3
93.1k
VOUT2
1.5V
VSUPPLY
3.6V
VOUT3
0.8V
R4
107k
R1
59k
R2
118k
R7
162k
R8
76.8k
3
5
2
12
15
7
13
11
9
8
10
14
6
L3
4.7
μH
C3
4.7
μF
R6
100k
RUN200B
VCC
LTC3544
PVIN
GNDA
PGND
SW200B
SW200A
VFB200B
VFB200A
RUN200A
RUN100
SW100
SW300
VFB100
VFB300
RUN300
Figure 5. Design Example
LOAD CURRENT (A)
30
90
100
20
10
80
50
70
60
40
0.0001
0.01
0.1
1
3544B F05b
0
0.001
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VOUT = 2.5V
TA = 25°C
Efficiency vs Output Current—300mA Channel,
All Other Channels Off
Transient Response
VOUT300
50mV/DIV
AC COUPLED
IL
250mA/DIV
ILOAD
250mA/DIV
20
μs/DIV
VIN = 3.6V
VOUT = 2.5V
TA = 25°C
LOAD STEP = 300
μA TO 300mA
3544B F05c



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