LTC1627CS8 View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC1627CS8 Datasheet PDF : 16 Pages
| |||
LTC1627
APPLICATIONS INFORMATION
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 =
f
1
∆IL
VOUT
1
−
VOUT
VIN
(3)
Substituting VOUT = 2.5V, VIN = 4.2V, ∆IL = 200mA and
f = 350kHz in equation (3) gives:
( )( ) L =
2.5V
350kHz 200mA
1
−
2.5V
4.2V
=
14.5µH
A 15µH inductor works well for this application. For good
efficiency choose a 1A inductor with less than 0.25Ω
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
0.25Ω. 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:
R2
=
VOUT
0.8
−
1
•
R1 =
171k;
use
169k
Figure 8 shows the complete circuit along with its effi-
ciency curve.
CITH
47pF
CSS
0.1µF
1
ITH
SYNC/FCB 8
2
RUN/SS
7
VDR
3 VFB LTC1627 VIN 6
4
GND
5
SW
* SUMIDA CD54-150
** ZETEX BAT54S
† AVX TPSC107M006R0150
†† AVX TPSC226M016R0375
15µH*
R2
169k
1%
R1
80.6k
1%
C1
0.1µF
VOUT
2.5V
0.5A
+ COUT†
100µF
6.3V
BAT54S**
D1
VIN
2.8V TO
4.5V
+ CIN††
22µF
16V
D2
C2
0.1µF
1627 F08a
100
95
VIN = 3.6V
90
85
VIN = 4.2V
80
75
70
65
60
55
50 VOUT = 2.5V
45
1
10
100
OUTPUT CURRENT (mA)
Figure 8. Single Lithium-Ion to 2.5V/0.5A Regulator
1000
1627 F08b
12
Share Link: 