Datasheet

14
LTC3404
3404fb
Figure 8. Single Lithium-Ion to 2.5V/0.3A Regulator from Design Example
V
OUT
2.5V
*
**
***
47pF
10μF***
CER
6.2μH*
887k
22μF**
CER
412k
LTC3404
RUN
I
TH
V
FB
GND
8
7
6
5
1
2
3
4
PLL LPF
SYNC/MODE
V
IN
SW
V
IN
2.65V
TO 4.2V
TOKO D63LCB A920CY-6R2M
TAIYO-YUDEN CERAMIC JMK325BJ226MM
TAIYO-YUDEN CERAMIC LMK325BJ106MN
3404 F08a
20pF
TYPICAL APPLICATIO S
U
V
OUT
2.5V
0.6A
C
IN
***
10μF
CER
20pF
887k
C
OUT
**
22μF
CER
*
**
***
47pF
4.7μH*
LTC3404
RUN
I
TH
V
FB
GND
8
7
6
5
1
2
3
4
PLL LPF
SYNC/MODE
V
IN
SW
V
IN
3V TO 4.2V
TOKO D52LC A914BYW-4R7M
TAIYO-YUDEN CERAMIC JMK325BJ226MM
TAIYO-YUDEN CERAMIC LMK325BJ106MN
3404 TA03
412k
Single Li-Ion to 2.5V/0.6A Regulator
Using All Ceramic Capacitors
OUTPUT CURRENT (mA)
EFFICIENCY (%)
95
90
85
80
75
70
0.1 10 100 1000
3404 F8b
1.0
V
OUT
= 2.5V
L = 6.2μH
V
IN
= 3V
V
IN
= 4.2V
V
IN
= 3.6V
APPLICATIO S I FOR ATIO
WUUU
Substituting V
OUT
= 2.5V, V
IN
= 4.2V, ΔI
L
=120mA and
f = 1.4MHz in equation (3) gives:
L
V
MHz mA
V
V
H= −
⎛
⎝
⎜
⎞
⎠
⎟
= μ
25
1 4 120
1
25
42
6
.
.( )
.
.
A 6.2μH inductor works well for this application. For best
efficiency choose a 1A inductor with less than 0.25Ω
series resistance.
C
IN
will require an RMS current rating of at least 0.15A at
temperature and C
OUT
will require an ESR of less than
0.25Ω. In most applications, the requirements for these
capacitors are fairly similar.
For the feedback resistors, choose R1 = 412k. R2 can
then be calculated from equation (2) to be:
R
V
R k use
OUT
2
08
1 1 875 5 8= −
⎛
⎝
⎜
⎞
⎠
⎟
=
.
. ; 87k
Figure 8 shows the complete circuit along with its effi-
ciency curve.