LTC3405 Linear Technology, LTC3405 Datasheet - Page 13

• Manufacturer Part Number: LTC3405
• Description: Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger
• Manufacturer: Linear Technology

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APPLICATIO S I FOR ATIO
Substituting V
f = 1.5MHz in equation (3) gives:
For best efficiency choose a 300mA or greater inductor
with less than 0.3 series resistance.
C
I
of less than 0.6 and greater than 0.1 . In most cases,
a tantalum capacitor will satisfy this requirement.
TO 4.2V
TYPICAL APPLICATIO S
LOAD(MAX)
IN
2.7V
V
L
will require an RMS current rating of at least 0.125A
IN
1 5
.
C
2.2 F
CER
MHz
IN
/2 at temperature and C
100
†
90
80
70
60
50
40
30
0.1
2 5
OUT
.
(
4
1
6
100
V
V
IN
V
RUN
MODE
IN
= 4.2V
= 2.5V, V
LTC3405
U
mA
GND
OUTPUT CURRENT (mA)
1
2
)
V
SW
Figure 11a
V
FB
IN
1
U
= 2.7V
3
5
10
IN
TO 4.2V
2 5
4 2
412k
6.8 H*
3405 F11a
2.7V
V
= 4.2V, I
.
.
22pF
887k
V
IN
IN
V
V
= 3.6V
OUT
U
100
W
** AVX TPSB336K006R0600
*SUMIDA CMD4D11-6R8MC
†
Optimized for Small Footprint and High Efficiency
3405 TA01b
TAIYO YUDEN LMK212BJ225MG
will require an ESR
C
1 F
CER
6 8
+
IN
.
**
1000
L
Single Li-Ion to 1.8V/300mA Regulator
C
33 F
TANT
= 100mA and
H
OUT
4
1
6
**
V
2.5V
V
RUN
MODE
U
OUT
IN
LTC3405
GND
2
SW
V
FB
3
5
1M
200k
3405 TA01a
4.7 H*
For the feedback resistors, choose R1 = 412k. R2 can
then be calculated from equation (2) to be:
Figure 11 shows the complete circuit along with its
efficiency curve.
22pF
332k
**
*
†
MURATA LQH3C4R7M34
TAIYO YUDEN CERAMIC JMK107BJ105MA
TAIYO YUDEN CERAMIC JMK212BJ475MG
R
2
AC COUPLED
100mV/DIV
200mA/DIV
200mA/DIV
I
V
V
LOAD
OUT
0 8
100
OUT
C
4.7 F
CER
90
80
70
60
50
40
30
I
OUT
.
L
0.1
V
1.8V
V
I
OUT
LOAD =
†
IN
V
= 3.6V
IN
1 1 875 5
= 4.2V
100mA TO 250mA
R
OUTPUT CURRENT (mA)
1
V
IN
Figure 11b
= 2.7V
V
40 s/DIV
IN
= 3.6V
10
. ;
k use
100
3405 TA01c
3405 F11b
8
87k
LTC3405
1000
sn3405 3405fs
13