LTC3409 LINER [Linear Technology], LTC3409 Datasheet - Page 14

• Manufacturer Part Number: LTC3409
• Description: 600mA Low Vin Buck Regulator in 3mm x 3mm DFN
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTC3409
Design Example
As a design example, assume the LTC3409 is used in a
2-alkaline cell battery-powered application. The V
operating from a maximum of 3.2V down to about 1.8V.
The load current requirement is a maximum of 600mA but
most of the time it will be in standby mode, requiring only
2mA. Efficiency at both low and high load currents is
important. Output voltage is 1.5V. With this information
we can calculate L using Equation 2:
Substituting V
f = 1.7MHz in Equation 2 gives:
1.6V TO 5.5V
14
L
L
=
=
V
IN
1 7
f
.
•
1
∆
MHz
I
L
V
C
4.7µF
OUT
IN
OUT
1
•
240
= 1.5V, V
U
⎛
⎜
⎝
1
mA
–
133k
R2
V
1 5 1
V
U
OUT
.
IN
IN
⎛
⎜
⎝
⎞
⎟
⎠
191k
10pF
R1
C1
= 3.2V, ∆I
–
V
GND
V
V
FB
IN
IN
LTC3409
1 5
3 2
.
.
W
MODE
SYNC
⎞
⎟ ≅
⎠
RUN
L1: SUMIDA CDRH2D18/LD
SW
2 2
L
.
= 240mA and
µ
H
U
2.2µH
IN
L1
will be
(2)
Figure 4
3409 F04
For best efficiency choose a 750mA or greater inductor
with less than 0.3Ω series resistance. C
RMS current rating of at least 0.3A ≅ I
temperature.
For the feedback resistors, choose R2 = 133k. R1 can then
be calculated from Equation 2 at 191K. Figure 4 shows the
complete circuit along with its efficiency curve.
Table 2 below gives 1% resistor values for selected output
voltages.
C
10µF
CER
OUT
V
1.5V
0.6A
0.85V
OUT
V
1.2V
1.5V
1.8V
OUT
100
90
80
70
60
50
40
30
20
10
0
0.1
Burst Mode Efficiency, 1.5V
51.1k
1.8V
127k
191k
255k
R1
IN
1
LOAD CURRENT (mA)
2.5V
IN
3.2V
10
IN
IN
LOAD(MAX)
will require an
133k
133k
133k
133k
100
R2
OUT
3409 F04b
/2 at
1000
3409f