LTC1879 LINER [Linear Technology], LTC1879 Datasheet - Page 16

• Manufacturer Part Number: LTC1879
• Description: 1.2A Synchronous Step-Down Regulator with 15mA Quiescent Current
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTC1879
Design Example
As a design example, assume the LTC1879 is used in a
dual lithium-ion battery-powered cellular phone applica-
tion. The V
down to about 2.65V. The load current requirement is a
maximum of 0.7A but most of the time it will be on standby
mode, requiring only 2mA. Efficiency at both low and high
load currents is important. Output voltage is 2.5V. With
this information we can calculate L using equation (1),
Substituting V
f = 550kHz in equation (3) gives:
16
L
L
550
f
1
IN
kHz
I
L
2 5
will be operating from a maximum of 8.4V
OUT
.
•
V
V
210
OUT
= 2.5V, V
U
mA
1–
U
V
1
V
OUT
–
IN
IN
2 5
8 4
= 8.4V, I
.
.
V
V
W
15 2
L
.
= 210mA and
H
U
(3)
An 15 H inductor works well for this application. For good
efficiency choose a 1.5A inductor with less than 0.125
series resistance.
C
temperature and C
0.125 . In most applications, the requirements for these
capacitors are fairly similar.
For the feedback resistors, choose R2 = 412k. R1 can then
be calculated from equation (2) to be:
Figure 9 shows the complete circuit along with its effi-
ciency curve.
IN
R
will require an RMS current rating of at least 0.35A at
1
V
0 8
OUT
.
–
1
OUT
•
R
2 875 5
will require an ESR of less than
. ,
k use
887
k
1879f