LTC1627 Linear Technology, LTC1627 Datasheet - Page 12

• Manufacturer Part Number: LTC1627
• Description: Monolithic Synchronous Step-Down Switching Regulator
• Manufacturer: Linear Technology

APPLICATIONS
LTC1627
3. Does the (+) plate of C
4. Keep the switching node SW away from sensitive small-
Design Example
As a design example, assume the LTC1627 is used in a
single lithium-ion battery-powered cellular phone applica-
tion. The V
down to about 2.7V. The load current requirement is a
maximum of 0.5A 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 = 350kHz in equation (3) gives:
** ZETEX BAT54S
12
††
* SUMIDA CD54-150
†
AVX TPSC107M006R0150
AVX TPSC226M016R0375
0.1 F
possible? This capacitor provides the AC current to the
internal power MOSFETs.
signal nodes.
L
47pF
C
C
SS
ITH
f
1
IN
I
1
2
3
4
L
will be operating from a maximum of 4.2V
OUT
I
RUN/SS
V
GND
TH
V
FB
OUT
LTC1627
= 2.5V, V
U
SYNC/FCB
1
V
INFORMATION
SW
V
DR
IN
IN
U
V
V
OUT
IN
8
7
6
5
connect to V
IN
= 4.2V, I
15 H*
80.6k
W
169k
1%
1%
R1
R2
IN
L
C1
0.1 F
+
Figure 8. Single Lithium-Ion to 2.5V/0.5A Regulator
= 200mA and
as closely as
C
100 F
6.3V
V
2.5V
0.5A
OUT
U
OUT
†
BAT54S**
(3)
D1
D2
A 15 H inductor works well for this application. For good
efficiency choose a 1A inductor with less than 0.25
series resistance.
C
temperature and C
0.25 . In most applications, the requirements for these
capacitors are fairly similar.
For the feedback resistors, choose R1 = 80.6k. R2 can then
be calculated from equation (2) to be:
Figure 8 shows the complete circuit along with its effi-
ciency curve.
IN
C2
0.1 F
1627 F08a
L
R
will require an RMS current rating of at least 0.25A at
2
+
350
C
22 F
16V
IN
V
2.8V TO
4.5V
V
IN
††
0 8
OUT
kHz
2 5
V
200
1
OUT
mA
R
100
1 171 use 169k
will require an ESR of less than
95
90
85
80
75
70
65
60
55
50
45
1
V
1
OUT
= 2.5V
k
2 5
4 2
OUTPUT CURRENT (mA)
V
V
10
V
V
IN
IN
= 3.6V
= 4.2V
14 5
100
H
1627 F08b
1000