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LTC1627CS8 Datasheet(PDF) 12 Page - Linear Technology

Part # LTC1627CS8
Description  Monolithic Synchronous Step-Down Switching Regulator
PDF  16 Pages
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Manufacturer  LINER [Linear Technology]
Direct Link  http://www.linear.com
Logo LINER - Linear Technology

LTC1627CS8 Datasheet(HTML) 12 Page - Linear Technology

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LTC1627
3. Does the (+) plate of CIN connect to VIN as closely as
possible? This capacitor provides the AC current to the
internal power MOSFETs.
4. Keep the switching node SW away from sensitive small-
signal nodes.
Design Example
As a design example, assume the LTC1627 is used in a
single lithium-ion battery-powered cellular phone applica-
tion. The VIN will be operating from a maximum of 4.2V
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),
L
fI
V
V
V
L
OUT
OUT
IN
= ()( )
−


1
1
∆
(3)
Substituting VOUT = 2.5V, VIN = 4.2V, ∆IL = 200mA and
f = 350kHz in equation (3) gives:
APPLICATIONS INFORMATION
L
V
kHz
mA
V
V
H
= ()(
)
−


=
25
350
200
1
25
42
14 5
..
.
.µ
A 15
µH inductor works well for this application. For good
efficiency choose a 1A inductor with less than 0.25
Ω
series resistance.
CIN will require an RMS current rating of at least 0.25A at
temperature and COUT will require an ESR of less than
0.25
Ω. 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:
R
V
Rk
OUT
2
08
1
1 171
=−


•=
.
; use 169k
Figure 8 shows the complete circuit along with its effi-
ciency curve.
CSS
0.1
µF
COUT
†
100
µF
6.3V
CIN
††
22
µF
16V
C1
0.1
µF
C2
0.1
µF
D2
D1
BAT54S**
15
µH*
* SUMIDA CD54-150
** ZETEX BAT54S
† AVX TPSC107M006R0150
†† AVX TPSC226M016R0375
R2
169k
1%
R1
80.6k
1%
CITH
47pF
1
2
3
4
8
7
6
5
SYNC/FCB
VDR
VIN
SW
ITH
RUN/SS
VFB
GND
LTC1627
VIN
2.8V TO
4.5V
VOUT
2.5V
0.5A
1627 F08a
+
+
OUTPUT CURRENT (mA)
1
100
1000
1627 F08b
10
100
95
90
85
80
75
70
65
60
55
50
45
VOUT = 2.5V
VIN = 3.6V
VIN = 4.2V
Figure 8. Single Lithium-Ion to 2.5V/0.5A Regulator



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