LTC3405A-1.375_15 Datasheet, PDF (11/12 Pages) Linear Technology – 1.375V, 1.5MHz, 300mA Synchronous Step-Down Regulators in ThinSOT

APPLICATIO S I FOR ATIO
Substituting V_OUT = 1.375V, V_IN = 4.2V, ∆I_L = 60mA and
f = 1.5MHz in equation (3) gives:
L
=
1.375V
1.5MHz(60mA)
⎛
⎝⎜^1−
1.375V
4.2V
⎞
⎠⎟
≅
10µH
V_OUT
VIA TO V_IN
V_IN
PIN 1
LTC3405A-1.375
L1 ^SW
C_OUT
C_IN
GND
3405A1518 F04
Figure 4. LTC3405A-1.375 Suggested Layout
For best efficiency choose a 200mA or greater inductor
with less than 0.3Ω series resistance.
C_IN will require an RMS current rating of at least 0.125A
≅ I_LOAD(MAX)/2 at temperature and C_OUT will require an
ESR of less than 0.5Ω. In most cases, a ceramic capacitor
will satisfy this requirement.
Figure 5 shows the complete circuit along with its effi-
ciency curve.
V_IN
2.7V
TO 4.2V
C_IN***
2.2µF
CER
4
V_IN
3 ^10µH*
SW
V_OUT
1.375V
LTC3405A-1.375
1
RUN
6
MODE
5
V_OUT
C_OUT**
10µF
CER
GND
* MURATA LQHMCN10002
** MURATA 0603 GRM188R60G106ME47B
2
*** MURATA 0603 GRM188R61A225KE34B
3405A1375 F05a
Figure 5a. Small Footprint Application
LTC3405A-1.375
100
90
80
70
60
50
40
30
20
10
0
0.1
V_IN = 2.7V
V_IN = 3.6V
V_IN = 4.2V
1
10
100
LOAD CURRENT (mA)
1000
3405A1375 F05b
Figure 5b. LTC3405A-1.375 Small Footprint Efficiency
V_OUT
100mV/DIV
AC
COUPLED
I_L
200mA/DIV
I_LOAD
200mA/DIV
V_IN = 3.6V
20µs/DIV
I_LOAD = 100mA TO 300mA
Burst Mode OPERATION
Figure 5c.
3405A1375 F05c
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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