LTC3544EUD-TRPBF データシートの表示（PDF） - Linear Technology
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LTC3544EUD-TRPBF
Linear Technology
LTC3544EUD-TRPBF Datasheet PDF : 16 Pages
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LTC3544
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:
L4
=
2.5V
2.25MHz • 100mA
⎛⎝⎜1–
2.5V⎞
4.2V⎠⎟
=
4.5µH
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:
R8
=
⎛ VOUT
⎝⎜ 0.8
– 1⎞⎠⎟
• R7
=
163.2k
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.
VOUT2
1.5V
VOUT3
0.8V
VSUPPLY
3.6V
C2
4.7μF
R3
93.1k
R4
107k
C3
R6
4.7μF 100k
L2
4.7μH
C6
20pF
L3
4.7μH
C9
4.7μF
15
7
C10
4.7μF
16
VCC
RUN200B
4 SW200B
PVIN
12
RUN100
SW100 13
1 VFB200B
3
RUN200A
5 SW200A
LTC3544
VFB100 11
9
RUN300
SW300 8
2 VFB200A
GNDA
14
PGND
6
VFB300 10
L1
10μH
L4
4.7μH
Figure 5. Design Example
C5 R1
20pF 59k
R2
118k
VOUT1
1.2V
C1
4.7μF
C8 R7
20pF 162k
R8
76.8k
VOUT2
2.5V
C4
10μF
3544 F05a
Efficiency vs Output Current—300mA Channel,
All Other Channels Off
100
90
80
70
60
50
40
30
20
10 VOUT = 2.5V
TA = 25°C
0
0.0001 0.001
0.01
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
0.1
1
LOAD CURRENT (A)
3544B F05b
14
Transient Response
VOUT300
50mV/DIV
AC COUPLED
IL
250mA/DIV
ILOAD
250mA/DIV
VIN = 3.6V
20μs/DIV
VOUT = 2.5V
TA = 25°C
LOAD STEP = 300μA TO 300mA
3544B F05c
3544fa
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